Radar Test Board Overview

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General
Project
BOM
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Here is a concise, system-level explanation of the project, using what’s in your schematic and BOM.
Purpose
  • A 24 GHz CW/FMCW radar test board that transmits and receives at 24 GHz, brings baseband I/Q (in-phase and quadrature) down to analog IF, conditions it with selectable gains, and digitizes/controls it with a microcontroller. It also exposes RF via SMA for lab instruments and uses an automotive 12 V input with on-board 5 V and 3.3 V rails.
Core components and how they interact

Table

BlockDesignatorsRoleKey connections
24 GHz radar transceiverU3RF front end with TX, RX, baseband I/Q outputs, tuning inputTX↔J4 (ANT_TX), RX↔J5 (ANT_RX), IFI/IFQ → U2, V_TUNE ← U6 output
IF/baseband conditioningU2Quad op-amp stages for IFI/IFQ: gain, buffering, filteringIFI/IFQ from U3; outputs to MCU analog pins and/or switches
Gain/path selectionU7, U8Dual bilateral analog switches to gate/multiplex high/low‑gain I/Q pathsSwitches steer Out_IL/Out_QL/O_IH/O_QH from U2 to the MCU and test points
MCU and controlU4Sampling IF channels, SPI/JTAG/I2C connectivity, DAC_PWM for VCO tuneADC inputs on PA5/PA6, PWM DAC on PB4 → V_TUNE chain; JTAG via J1; SPI via J2; I2C via J3; clock via Y1
PWM-to-DC tune chainR30, R31, C25, C26, U6Two-stage RC low-pass and op-amp buffer to convert MCU PWM into a stable V_TUNE for U3DAC_PWM → RC1 → RC2 → U6 → FREQ_TUNE net → U3
Power: 12 V in, 5 V, 3.3 V railsD1, U1, U5, bulk caps C1/C22/C23Reverse-polarity + surge headroom, 12 V → 5 V regulation, then 5 V → 3.3 V for RF/MMCU12V → D1 → U1 (5 V) → U5 (3.3 V)
RF interfacesJ4, J550 Ω SMA end-launch for TX/RX to instruments/antennasDirect to U3 TX/RX pins
Debug/programJ1, J2, J3, clock Y1JTAG, SPI header, I2C header; stable MCU clockJTAG TMS/TCK/TDI/TDO, SPI MOSI/MISO/SCK, I2C SDA/SCL; XTAL1/2 nets to Y1
Design and implementation details
  • RF front end: U3 TX goes to J4 and RX to J5. Baseband IF nets IFI and IFQ leave U3 and feed the multi-stage analog chain in U2.
  • IF signal conditioning: U2 implements high‑/low‑gain paths and filtering for both I and Q, creating IFI_HG/LG and IFQ_HG/LG nets. Selection/gating is handled by the analog switches U7 and U8, which route the appropriate outputs toward the MCU inputs and/or measurement points.
  • Tuning control (VCO sweep/offset): The MCU’s PWM (DAC_PWM) is smoothed by cascaded RCs R30/C25 and R31/C26, then buffered by U6 to drive U3 V_TUNE (FREQ_TUNE net). This provides a DC‑accurate control voltage from a digital PWM source for CW/FMCW modes.
  • Processing and I/O: U4 reads analog IF channels (e.g., PA5/PA6), controls prescaler/divider signals, and exposes JTAG (J1), SPI (J2), and I2C (J3) for configuration and data.
  • Power tree: 12 V input is protected by D1. U1 generates 5 V (bulk reservoirs C1, C22), and U5 generates 3.3 V (reservoir C23) for the RF/MMCU domains.
Key technologies, dependencies, design choices, and trade-offs
  • 24 GHz RF with SMA breakouts: End‑launch J4/J5 simplifies lab bring‑up and antenna swaps but requires impedance‑controlled launch and tight ground referencing to avoid mismatch and radiation.
  • Analog IF chain with selectable gain: Using U2 plus U7/U8 is flexible and low‑cost. Trade‑offs include switch on‑resistance/capacitance adding noise/bandwidth limits and the JFET‑op‑amp’s noise/offset/PSRR vs modern low‑noise, rail‑to‑rail alternatives.
  • PWM DAC for V_TUNE: The two‑stage RC plus U6 buffer is inexpensive and firmware‑simple. Trade‑offs are ripple/leakage, settling time, and temperature drift; the filter corner must balance ripple suppression with tuning agility for FMCW sweeps.
  • Power via cascaded LDOs: U1 → U5 is clean and RF‑friendly but thermally inefficient from 12 V. It’s robust for a bench/automotive test setting; thermal rise and load dump transients should be reviewed.
  • Testability: Breaking out RF and digital/programming headers (J1, J2, J3) accelerates bring‑up and iteration.
Potential challenges and performance considerations
  • 24 GHz layout discipline: Launch geometry, reference plane continuity, solder mask control around J4/J5, and short RF paths to U3 are critical to avoid mismatch and parasitic radiation.
  • IF noise and dynamic range: Low‑frequency flicker noise, switch on‑resistance/capacitance, and op‑amp input noise set the floor. Ensure anti‑aliasing and bandwidth align with IF content and ADC sampling.
  • V_TUNE purity: Residual PWM ripple or long settling in the R30/R31/C25/C26 network can modulate the VCO, causing FM spurs and range/Doppler artifacts. Place these parts close to U6 and U3 with a clean analog ground.
  • Power integrity and EMI: The 12 V to 5 V drop in U1 and 5 V to 3.3 V in U5 dissipate heat; decoupling and bulk (C1, C22, C23) location matters for load steps (TX on/off).
  • Crosstalk/grounding: Close analog/digital domains and switchable paths can couple; partition grounds and route IF returns directly; minimize loop areas around U2, U7, U8.
Real-world applications
  • Blind‑spot bicyclist detection on parked cars, occupancy sensing, short‑range motion profiling, and lab validation of CW/FMCW algorithms using the SMA breakouts and MCU‑captured I/Q.
Suggestions for improvement and future enhancements
  • Signal chain
    • Evaluate U2 stage noise/bandwidth vs your IF targets; consider consolidating gain control to minimize switch parasitics via fewer stages.
    • Refine the PWM‑DAC filter (R30, R31, C25, C26) for spur suppression vs sweep agility; verify ripple at the V_TUNE pin of U3.
  • Power and robustness
    • Review thermal headroom in U1/U5 at worst‑case input and load. Consider surge/load‑dump resilience at the 12 V entry ahead of D1.
  • Layout/EMC
    • Tighten the RF launches around J4/J5; add keepouts and stitching vias as needed; keep U3 decoupling ultra‑local.
    • Consider shielding can provisions over U3 and the IF chain.
  • System/firmware
    • Add calibration routines (DC offset, I/Q imbalance, phase calibration vs temperature). Use the prescaler/divider output from U3 for sweep linearization feedback if applicable.
    • Provide firmware hooks to switch U7/U8 paths during runtime for auto‑range.
If you’d like, I can review specific subcircuits—for example the PWM‑to‑V_TUNE filter or the IF op‑amp stages—and suggest concrete component values and placement guidelines.
Op amp search
LDO alternative
Power dissipation calc
RF layout guidelines
Ground partitioning advice
76 days

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give me pinout for AVR JTAG
roytaylor

roytaylor

@copilot give me pinout for AVR JTAG
1y

copilot

The AVR JTAG (Joint Test Action Group) interface is used for on-chip debugging and programming of AVR microcontrollers. The standard JTAG interface for AVR microcontrollers consists of the following pins:
  1. TCK (Test Clock) - provides the clock signal to the TAP (Test Access Port).
  2. TDI (Test Data In) - used to send data into the device’s test logic.
  3. TDO (Test Data Out) - used to send data out of the device’s test logic.
  4. TMS (Test Mode Select) - used to change the state of the TAP controller.
  5. TRST (Test Reset, optional) - resets the TAP controller. Not all AVR devices support this pin.
  6. GND (Ground) - Common ground.
  7. VCC or VREF (Power Supply for Input Thresholds) - Provides the reference voltage for the JTAG interface; it is not used to power the device.
An example of a basic connection for AVR’s JTAG interface excluding TRST (if not used or unavailable on the specific AVR model) would be:
  • TCK to JTAG TCK pin on AVR
  • TDI to JTAG TDI pin on AVR
  • TDO to JTAG TDO pin on AVR
  • TMS to JTAG TMS pin on AVR
  • GND to Ground pin on AVR
  • VCC/VREF to the voltage reference (often connected to VCC of the target board)
Keep in mind that the actual pin numbers for these signals can vary widely among different AVR chips. Always refer to the specific datasheet for your AVR microcontroller to find the exact JTAG pin configuration.
1y
is there a way to hide a schematic symbol and only leave the name?
roytaylor

roytaylor

@copilot is there a way to hide a schematic symbol and only leave the name?
1y

copilot

In the context of using Flux.ai for designing electronic schematics and PCB layouts, hiding a schematic symbol while retaining its name or label isn't directly supported as a singular action. Schematic symbols are used primarily for their visual representation in the schematic layout to convey connections and function. Typically, removing or hiding a symbol would remove that visual information, which is crucial for understanding the circuit's functionality.
However, there are a few alternative approaches you could consider to achieve a similar effect or manage the visual clutter in your schematic:
  1. Use Notes or Text Labels: Instead of hiding the symbol, you might consider using minimalistic symbols (if available) and relying heavily on text labels or note annotations for component identification and additional details. This approach keeps the schematic legible but reduces visual complexity.
  2. Organize with Blocks or Hierarchical Design: For complex schematics, consider organizing components into functional blocks or using a hierarchical design approach. This methodology involves creating sub-circuits that can be represented as single blocks on the main schematic. Each block can be labeled with names or identifiers. Double-clicking on a block would then open the detailed schematic of that sub-circuit. While this doesn't hide symbols per se, it simplifies the main schematic view.
  3. Custom Components: Although it might require extra effort, creating custom schematic symbols that are visually minimalistic (or perhaps just a box with the component name) could be a workaround. This way, you can ensure that the schematic looks cleaner while retaining essential identifying information.
  4. Documentation Layers: Depending on the flexibility of the CAD tool, you might be able to use layers dedicated to documentation or comments. While not exactly hiding existing symbols, you could possibly overlay or associate simple text objects with parts on these layers, emphasizing the names over the symbols. This would depend on the capability to control the visibility of layers within the software.
Remember that the primary goal of a schematic is to communicate the circuit design clearly. If you're simplifying for presentation purposes, ensure that the essential electrical and connectivity information remains accessible, either in the simplified main schematic or in detailed sub-circuits/documentation.
Since software capabilities and features can evolve, it's also worth checking the latest documentation or support resources for Flux.ai for any new features that might directly support your needs.
1y
10
are there any passive generic components that I may not find a component for on ...
roytaylor

roytaylor

@copilot are there any passive generic components that I may not find a component for on this?
1y

copilot

In your project, most of the passive components are specified with common values and packages, which should be readily available as components in most electronic design tools, including Flux. However, there might be some general considerations and exceptions to keep in mind when working with passive components in any design software:
  1. Custom or Non-standard Values: If you're using highly specific, non-standard values for resistors, capacitors, or inductors that aren't typically stocked by manufacturers or distributors, you might not find an exact match in the component library. In these cases, you may have to select the closest available component and adjust your design accordingly or add a custom component to the library if the software allows.
  2. Specific Physical Sizes or Tolerances: Some designs might require components with precise physical dimensions for tight layout constraints or specific tolerances for critical applications. Ensure that the selected components in the design tool match these requirements. If not, you may need to manually adjust or look for alternate components.
  3. Advanced Materials or Technologies: Certain advanced materials (like High-Q capacitors, ultra-low ESR capacitors, or precision thin-film resistors) or technologies (such as RF-specific inductors) might not be represented as generic components. These would require specific part numbers and might need to be imported or created as custom components in your design tool.
For your design, common components like SMD resistors (R1-R31), ceramic capacitors ($C1, C2, C3$, etc.), and electrolytic capacitors (For example, $C12, C14$) are widely used and should be available in Flux. If you do encounter a component that isn’t in Flux's library:
  • Use a Generic Component: Many design tools, including Flux, allow you to use a generic component with the possibility of specifying the values and sometimes even the footprint manually.
  • Create a Custom Component: If a specific component is crucial for your design and isn’t available, you might need to create a custom component. This typically involves defining the electrical properties, footprint, and 3D model if necessary.
Remember, when in doubt or if you're using a component with tight performance specifications, always double-check the manufacturer's datasheets and ensure that the selected or created component in your design tool accurately represents what you plan to use in the real-world application.
1y
12
Find a subsitution for U1 with the same package
roytaylor

roytaylor

@copilot Find a subsitution for U1 with the same package
1y

copilot

For substituting U1, which is an IFX25401TEV50ATMA1 from Infineon Technologies, we need to consider a regulator that matches its key characteristics and package. The IFX25401TEV50ATMA1 is a low dropout voltage regulator (LDO) with certain specific features:
  • Input Voltage $I$: This dictates the range of input voltages the regulator can handle.
  • Enable pin $EN$: A control pin used to enable or disable the output.
  • Ground $GND$: The common reference point for all circuitry in the device.
  • No Connect $NC$: A pin not internally connected, serving no function in this product version.
  • Output $Q$: The regulated output voltage pin.
Additionally, this component is in a package that is not directly mentioned but inferred to be compatible with automotive applications and has a specific output voltage of 5V.
A suitable substitution would require:
  • Matching or compatible input voltage range.
  • An output voltage of 5V, as that is the specific part number designation $50$ in IFX25401TEV50ATMA1 indicates a 5.0V output.
  • The presence of an enable pin function, to allow for similar power management capabilities.
  • Compatible ground and no-connect configurations.
  • Package compatibility to ensure physical fitting and thermal properties match the original design requirements, though the specific package for U1 is not listed, we will assume a common automotive-grade package for LDOs such as DPAK or similar.
Assuming we require a similar automotive-grade LDO regulator, one potential substitute could be the TPS7A4501 from Texas Instruments. However, without the specific package details of U1, recommending a direct substitute is challenging. The TPS7A4501 offers:
  • An output voltage range up to 20V, which is adjustable down to 5V with external resistors.
  • An enable pin to control the output.
  • Suitable for automotive applications.
  • Available in several packages, including the TO-220, which is common for automotive power applications and may offer similar thermal and mounting characteristics to the U1's package.
Before selecting a substitute, check:
  • The package compatibility: Ensure that the substitute's physical dimensions and pinout match the original component's footprint on the PCB.
  • Output current requirements: Ensure the substitute can supply sufficient current for your application.
  • Thermal considerations: Verify that the substitute can handle the thermal load under operational conditions without overheating.
Remember, substituting a component in an automotive application requires carefully reviewing the datasheets to ensure all electrical, thermal, and regulatory requirements are met, especially concerning automotive standards for reliability and safety.
1y
14
I need a Dual Bilateral Analog Switch for this project to quickly charge capacit...
roytaylor

roytaylor

@copilot I need a Dual Bilateral Analog Switch for this project to quickly charge capacitors on startup, bypassing the large 100k resistor values for the 220uF capacitors (r21,r11,C18,C10)
1y

copilot

For your requirement of quickly charging the capacitors at startup, bypassing the large 100kΩ resistors ((R21), (R11)) associated with the 220uF capacitors ((C18), (C10)), a dual bilateral analog switch would indeed be a suitable solution. Considering your project components and requirements, I recommend using the CD4066B which is a quad bilateral switch. This component provides four independent switches for precision analog/digital multiplexing and demultiplexing. Though you mentioned a dual switch, the quad switch offers additional flexibility if you decide to expand the requirement or for future projects.
Specifications for CD4066B:
  • Switch Type: CMOS Quad Bilateral Switch
  • Control Voltage Range: ±5V to ±15V
  • On-state Resistance: Typically 100Ω (depends on (V_{DD}-V_{SS}) and (V_{CONTROL}))
  • Package Type: Available in DIP-14, SOIC-14, and other surface-mount packages
Connection Guidelines:
Given your project components, you would only need to utilize two switches from the CD4066B. The basic idea is to use the switch to temporarily connect the capacitor directly to the voltage supply, bypassing the resistor during startup. Once the capacitor is charged, you can turn off the switch to resume normal operation through the resistor.
  • Control Logic: Use a digital I/O from your microcontroller ((U4)) to control the switch. This could be set high at startup to close the switch, and brought low after a delay defined in your firmware.
Suggested Connections:
  • (CD4066B) Switch 1 IN/OUT to one terminal of (C18)
  • (CD4066B) Switch 1 OUT/IN to (5V) power net (for charging (C18))
  • (CD4066B) Switch 2 IN/OUT to one terminal of (C10)
  • (CD4066B) Switch 2 OUT/IN to (5V) power net (for charging (C10))
  • Control Pins of Switch 1 and 2 from (U4) digital I/O pins (e.g., (PD)-lines)
  • Ground the Unused Input/Output pins of the unused switches to avoid floating pins, which could potentially switch due to noise.
Firmware Strategy:
  1. On Startup: Set control pins high to bypass resistors (R21) and (R11), allowing (C18) and (C10) to charge rapidly.
  2. After Delay: Set control pins low, reverting to charging through (R21) and (R11), ensuring a slow, controlled charge if further top-up is necessary and for regular operation.
Advantages:
  • Flexibility in controlling charge times.
  • Minimal modification to existing schematic.
Consideration:
Ensure the control voltage and switching signals are within the specification for the CD4066B to effectively switch without causing any unintended consequences on the analog signal paths.
This approach neatly integrates into your project, allowing quick capacitor charging on startup without permanently altering the circuit's behavior or performance in its standard operation.
1y
roytaylor

roytaylor

any dual switches?
1y

copilot

If you specifically require a dual switch for your application, the DG412 or DG202 could be more aligned with your needs, offering dual bilateral analog switches in a smaller package compared to the quad switch CD4066B. These components are designed to connect or disconnect analog or digital signals efficiently.
DG412 Specifications:
  • Switch Type: Precision Monolithic Quad SPST CMOS Analog Switch
  • Control Voltage Range: ±4.5V to ±20V
  • On-state Resistance: Typically 100Ω
  • Package Type: Available in 16-pin PDIP, SOIC, and TSSOP packages
Since DG412 is a quad switch and considering there isn't a standard "dual" version of DG412 explicitly, each DG412 switch can be used independently, leaving the unused switches unconnected (although it's good practice to tie unused inputs to ground or a defined logic level).
DG202 Specifications:
  • Switch Type: Dual SPST CMOS Analog Switch
  • Control Voltage Range: ±4.5V to ±18V
  • On-state Resistance: Typically 85Ω
  • Package Type: Available in 14-pin PDIP, SOIC
For your application, using either parts of a DG412 or DG202 would allow you to directly replace the quad switch recommendation with a component that has only dual switches to control, which might better suit your project size or complexity requirements.
Suggested Connections (Using DG202 as an example):
  • DG202 Switch 1 IN/OUT to one terminal of (C18)
  • DG202 Switch 1 OUT/IN to (5V) power net (for charging (C18))
  • DG202 Switch 2 IN/OUT to one terminal of (C10)
  • DG202 Switch 2 OUT/IN to (5V) power net (for charging (C10))
  • Control Pins of Switches 1 and 2 from (U4) digital I/O pins
Firmware Strategy remains the same:
  1. On Startup: Activate switches to bypass resistors (R21) and (R11), enabling (C18) and (C10) to charge rapidly.
  2. After Delay: Deactivate switches to revert to charging through resistors for normal operation.
Why Choose DG202 or DG412:
  • DG202 is a straight fit for dual switch requirements without unused switch sections, simplifying design and minimizing potential unused inputs handling.
  • DG412 offers additional switches that can be utilized for future expansion or other purposes within the same package, offering a form of "design headroom."
Pin Configuration Advice:
Ensure to consult the datasheet for exact pin configurations and to apply correct logic levels to control pins for switching actions, maintaining compliance with your project voltages and the switch's specifications.
1y
roytaylor

roytaylor

I need one with low on-state resistance
1y

copilot

For applications requiring a dual bilateral analog switch with low on-state resistance, the ADG1433 by Analog Devices is an excellent choice. The ADG1433 features ultra-low on-state resistance and is designed for use in applications where low on-state resistance is critical.
ADG1433 Specifications:
  • Switch Type: Triple SPDT (Single Pole, Double Throw)
  • Control Voltage Range: 1.8V to 5.5V
  • On-state Resistance: Typically 0.7Ω (max 1.5Ω across the full temperature range)
  • Package Type: Available in 16-lead TSSOP and 16-lead QFN (4x4 mm) packages
While the ADG1433 is a triple SPDT switch rather than dual, its ultra-low on-state resistance makes it suitable for applications where minimizing voltage drop and power loss is key. You can use two of the three available switches for your purpose and leave the third one unused, or plan for future circuit expansion.
Suggested Connections:
  • ADG1433 Switch 1:
    • TERMINAL A to (5V) power supply (for charging (C18))
    • TERMINAL B to one terminal of (C18)
    • CONTROL to a digital I/O pin on (U4)
  • ADG1433 Switch 2:
    • TERMINAL A to (5V) power supply (for charging (C10))
    • TERMINAL B to one terminal of (C10)
    • CONTROL to a digital I/O pin on (U4)
Firmware Control:
  • On Startup: Drive the control pins high to close the switches. This action will connect (C18) and (C10) directly to the (5V) supply, allowing them to charge quickly and bypass the 100kΩ resistors ((R21) and (R11)).
  • After a Set Time: Drive the control pins low to open the switches, reverting the charge path through (R21) and (R11), for standard operation.
Advantages of ADG1433:
  • Ultra-low On-state Resistance: Reduces power loss and voltage drop across the switch, important for maintaining efficiency in power-sensitive designs.
  • CMOS Technology: Offers low power consumption.
  • High Switching Speed: Beneficial for applications requiring quick charging circuits.
Considerations:
  • Unused switch: Properly terminate the unused switch to prevent it from picking up noise. It's generally advised to connect unused inputs to a known state. Check the datasheet for recommendations on handling unused switch terminals.
  • Power Supply Compatibility: Ensure the (5V) power supply used for charging the capacitors does not exceed the maximum voltage rating of the ADG1433.
Implementation Note:
Before finalizing the ADG1433 for your design, consider reviewing its datasheet for detailed electrical characteristics, pin configuration, and application notes to ensure compatibility with your specific application needs, especially in terms of the control logic levels relative to your microcontroller ((U4)) operating voltage.
1y
roytaylor

roytaylor

What if i connect the capacitor to the output of U2 at pin one to the positive side of the capacitor such as c18, rather than directly to a voltage source?
1y

copilot

Connecting the positive side of capacitor (C18) directly to the output of (U2) at pin 1, instead of directly to a voltage source, could be an interesting approach depending on the behavior and functionality you require from your circuit. Considering (U2) is specified as a TL074CD, which is a quad low-noise JFET-input operational amplifier, here's how this configuration would behave and affect your circuit:
  1. Operational Mode of U2:
    • The operation of (U2) at pin 1 depends on the rest of the operational amplifier's configuration. Pin 1 is the output of the first amplifier within (U2). Its behavior (voltage level, impedance) will be determined by the input signal to this op-amp section and the feedback network connected to it.
  2. Controlling the Charge Path:
    • If you intend to use (U2)'s output to quickly charge (C18), you are essentially using the op-amp's output to provide the charge current. This method would work under certain conditions:
      • The op-amp must be configured to source enough current to rapidly charge the capacitor.
      • The voltage at the op-amp's output must be sufficient to charge the capacitor to the desired level within your required timeframe.
  3. Considerations:
    • Current Capability: The TL074CD can source or sink a limited amount of current (typically in the range of 10mA to 40mA). You'll need to ensure this is sufficient to charge (C18) quickly without exceeding the op-amp's current capacity, which could lead to damage or operational failure.
    • Control Strategy: Unlike directly controlling a switch that connects a capacitor to a power supply, using an op-amp's output for charging requires that the op-amp be configured to provide the appropriate voltage. This could involve digital control (if the op-amp's input is digitally modulated) or analog control.
    • Voltage Consideration: The final voltage across (C18) will depend on the output voltage capability of (U2), which is influenced by its supply voltage and the design of the circuit around the op-amp.
  4. Benefits:
    • This approach could potentially simplify your circuit by eliminating the need for an additional switch component if you can meet the charging requirements through the op-amp alone.
    • Offers integrated control over the charging process through signal processing capabilities inherent to an operational amplifier.
  5. Challanges:
    • You'll need to carefully design the op-amp circuit to ensure it can safely and effectively charge the capacitor.
    • Risk of exceeding the op-amp's current limit, impacting both the op-amp and the overall circuit's performance.
In summary, while it's technically feasible to charge a capacitor like (C18) through the output of (U2), you must carefully consider the op-amp's limitations and ensure the circuit is designed to prevent damage while achieving the desired charging speed. Without knowing the entire circuit design around (U2), it's crucial to evaluate whether the op-amp can provide enough current and the right voltage level to efficiently charge (C18) and if this configuration aligns with the overall circuit behavior and performance requirements.
1y
roytaylor

roytaylor

It would still be switched by an analog switch, defaulting back to normal operation after charging time
1y

copilot

Given your intention to still use an analog switch for controlling the connection between the capacitor (e.g., (C18)) and the output of (U2) (TL074CD, a quad low-noise JFET-input operational amplifier) for the charging phase, and then defaulting back to normal operation after a set charging time, here's a refined approach to implementing this configuration:
Configuration Overview:
  • Charging Phase: During startup or a predefined condition, an analog switch connects (C18) to the output of (U2)'s first amplifier (pin 1), allowing the capacitor to charge more quickly than it would through its default resistor path. The output voltage of (U2) must be controlled to provide the desired charging voltage to (C18).
  • Normal Operation: After the charging phase, the analog switch disconnects (C18) from (U2), and the capacitor then operates in the circuit as initially intended, possibly through a resistor for slower charging/discharging or for signal processing purposes.
Steps and Considerations:
  1. Analog Switch Control:
    • The control signal for the analog switch can come from a digital I/O pin on your microcontroller ((U4)). For the charging phase, the microcontroller sets the control pin high, activating the switch. After the charging period, the control pin is set low, reverting to normal operation.
  2. Designing U2's Circuit:
    • The configuration of (U2) must ensure that its output (pin 1) can safely charge (C18). This involves setting the proper output voltage and ensuring the current capability matches the charging requirements without exceeding the op-amp's limits.
  3. Selecting an Analog Switch:
    • As previously discussed, for ultra-low on-state resistance, the ADG1433 can be an option, but considering you might be looking for a dual switch solution, and focusing on the charging aspect, consider implementing a switch like the ADG736 (CMOS, Low Voltage, Dual SPDT Switch), which provides a low on-state resistance and the dual-channel configuration you need. Each channel can be controlled independently.
  4. Possible Connection Scheme:
    • Analog Switch Channel 1:
      • Connect one terminal to (U2:OUT 1) (pin 1).
      • Connect the other terminal to the positive terminal of (C18).
      • Control pin connected to an I/O pin on (U4).
    • Operation:
      • For Charging: (U4) sets the control pin high, closing the switch, connecting (C18) to (U2)'s output.
      • For Normal Operation: (U4) sets the control pin low, opening the switch, isolating (C18) from (U2), and allowing it to function in its standard role within the circuit.
  5. Timing Considerations:
    • Implement a software delay in the microcontroller to manage the timing of the charging phase — for example, keeping the analog switch closed long enough for (C18) to charge to the required level.
Safety and Performance:
  • Verify the Maximum Current that (U2) can safely supply and ensure it matches your charging requirements.
  • Monitor the Capacitor Voltage during the charging phase to prevent overcharging, especially if (U2)'s output can exceed the capacitor's voltage rating.
  • Characterize the Charging Time in a prototype to adjust the timing in your microcontroller’s software for optimal performance.
This approach offers a smart way to accelerate capacitor charging via controlled conditions, leveraging both the analog switch for connectivity management and the operational amplifier for precise voltage application, with the flexibility to revert to normal operation post-charging.
1y
roytaylor

roytaylor

This also helps compared to charging it with 5v because the amplifier circuit will not reach 5v with the signal it is amplifying, and if the capacitor is greating than 5v then couldnt it lead to improper amplifications?
1y

copilot

Indeed, your consideration brings up important aspects of circuit design, particularly in the context of using operational amplifiers and charging capacitors within an analog signal chain. When using an operational amplifier (op-amp) like (U2) (the TL074CD) to directly charge a capacitor like (C18) in your circuit, there are several factors to consider:
  1. Output Voltage of Op-Amp: The output voltage that (U2) can supply to (C18) during the charging phase is inherently linked to the signal it's amplifying or the voltage level it is set to produce. If the op-amp is part of a circuit designed to produce lower voltages (for example, levels lower than (5V)), then using it to charge (C18) ensures that the capacitor doesn't receive a higher voltage than it typically would during operational conditions. This approach can be beneficial for maintaining signal integrity.
  2. Signal Integrity and Operational Behavior: Charging (C18) to a voltage level that reflects the operational peak voltage levels of (U2) helps in preserving signal integrity and preventing potential distortion or improper operation. If (C18) were charged to a voltage significantly higher than the operational voltage levels (e.g., (5V) in cases where the operational level doesn't reach (5V)), there could be a risk that the capacitor discharges back into (U2)'s output when it's not supposed to, potentially leading to improper amplifications or signal distortions.
  3. Capacitor's Voltage Rating: It's also vital to consider the voltage rating of (C18). While capacitors generally have a maximum voltage rating determining how much voltage they can safely handle, charging them to a level that aligns with their use in the circuit (i.e., not exceeding the voltage levels they would encounter during normal operation) is a prudent design choice. Charging a capacitor to a higher voltage than it ever reaches during operation doesn't offer benefits and could introduce risks if the voltage exceeds what connected components expect or can handle.
  4. Circuit Design Strategy: Your strategy takes advantage of the circuit's existing behavior and ensures that components are used within their intended operational context. This approach minimizes potential risks associated with incompatible voltage levels or unintended feedback paths.
In essence, charging (C18) using (U2)'s output, moderated through an analog switch for controlled timing, and limiting the charge to levels that are congruent with (U2)'s operational output, is a methodical way to integrate capacitor charging into the circuit's functionality without introducing discrepancies in voltage levels that could impede the circuit's intended operation. Always remember to consider the current-sourcing capability of (U2) and ensure that the charging configuration doesn't overburden the op-amp, adhering to safe design practices and component specifications.
1y
8
C15
Capacitance
15n F
C26
Capacitance
470n F
R13
Resistance
10k Ω
2V5
R15
Resistance
10k Ω
5V
O_QH
R17
Resistance
100k Ω
C27
Capacitance
0.1u F
Cap_IL
5V
5V
C12
Capacitance
220u F
DAC_PWM
R14
Resistance
1k Ω
IFI_LG
R21
Resistance
100k Ω
R24
Resistance
100k Ω
R30
Resistance
470 Ω
C11
Capacitance
15n F
C28
Capacitance
0.1u F
O_IH
Out_IL
C5
Capacitance
0.1u F
R10
Resistance
100k Ω
IFI_HG
C17
Capacitance
2700p F
Out_QL
Q_LSW
Cap_IH
R18
Resistance
1k Ω
C18
Capacitance
220u F
IFQ_LG
R22
Resistance
3.3k Ω
IFQ_HG
Cap_QL
R23
Resistance
33k Ω
R9
Resistance
100k Ω
C13
Capacitance
5600p F
R31
Resistance
1k Ω
5V
Cap_QH
3V3
2V5
C14
Capacitance
220u F
Cap_QL
Freq_Tune
Q_HSW
R19
Resistance
10k Ω
I_LSW
I_HSW
Cap_IH
C8
Capacitance
5600p F
C19
Capacitance
5600p F
O_IH
Cap_QH
Out_QL
IFQ
5V
C25
Capacitance
1u F
R16
Resistance
33k Ω
DAC V_follower
U2
End of Life
IFQ Low Gain
Bypass for init charging
IFI High Gain
U7
U6
U8
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Inspect

Cycle Sentry: 24-GHz Radar For Bicyclist Detection

Cycle Sentry: 24-GHz Radar For Bicyclist Detection
Description

Created
Last updated by roytaylor
1 Contributor(s)
roytaylor

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