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Recent content by zhangz64

  1. Z

    Decouple Cap selection for analog circuit

    i think this kind makes sense to me. Let us say i am designing a board with USB 5V as input source. I want to filter it out. How do i know the frequency of interests? Also, I have a 24Mhz uController on the board. Then does the noise are mostly 24Mhz switching noise?(provide if there is no...
  2. Z

    Decouple Cap selection for analog circuit

    Hi Everyone, I am trying to understand the how to select decoupling cap effectively. I see people put a lot of caps at input of their LDO or VDD of Analog IC to filter noise. Those cap are put in parallel and value ranges from 10uF to 12pF, I understand that those caps are meant to target...
  3. Z

    Minimize the noise on the board

    Thanks so much for the detailed reply. The board has 16 bit DAC with -/+ 1 LSB precision. Also i am using this DAC to generate bias current with V/C convertor. ( 10mV = 10uA, if I want to get 10uA accurately say 5% error, I think i will need to have noise less than 500uV) Yeah definitely...
  4. Z

    High efficiency and low noise 5V to 3.3V

    Hi Everyone. I am currently designing the power supply for my DC board. The board requires 600mA @3.3V and are supplied from 5v usb port (500mA @5V). Also the board consists many high resolution DAC that are sensitive to noise. To get down from 5V to 3.3V, if i used a buck, The noise maybe...
  5. Z

    Minimize the noise on the board

    Hi Everyone, I am currently struggling to determine the power supply for my board, and would really appreciate some inputs. the Board i am designing requires a High level of precision and consist of the following sub circuits. 1) High precision Bias Voltage from DAC 2) High precision Bias...
  6. Z

    ADC voltage/current sensing

    Hi KlausST, This may be a late reply. I did somehow manage to solve this issue by using a common mode filter at input and a filter at output. (I think the issue is that the noise get x100 amplified to the output, the ADC is picked up those noises) Therefore, I do have some questions...
  7. Z

    Programmable Current Sink(0mA to 1mA) with Low output voltage.

    Hi KlausT, I tested the circuit in the lab today, It worked as you suggested. I attached my measurement result here. I measured the voltage V_in after the Voltage divider. and measured the current at Rs2(current_m). then compare with current_c = V_in/Rs1, I have 2 additional questions: 1)...
  8. Z

    Programmable Current Sink(0mA to 1mA) with Low output voltage.

    Hi KlausT, Thanks for the detailed reply, Really appreciate it. I believe you mean the R2 and C6 in the circuit? What is causing the oscillation in the circuit and why would R2 and C6 reduce the oscillation? I simulated the transiant response, it looks stable. Is there any other situation i...
  9. Z

    Programmable Current Sink(0mA to 1mA) with Low output voltage.

    Hi, Thanks for the solution! I modified the circuit as you suggested. I used a NMOS instead of those 2 transistor. The simulation works well. I am planning to test the circuit out in lab tomorrow. Does the circuit make sense to you? Please let me know if you see any parts of the circuit that...
  10. Z

    Programmable Current Sink(0mA to 1mA) with Low output voltage.

    Hi Everyone, I am trying to design a programmable current sink with range from 0mA to 1mA. The current sink is used to sink current from the a PMOS current mirror, therefore the voltage at output should be around 0.3V. I designed the circuit with a DAC followed by a Voltage to Current...
  11. Z

    [SOLVED] [moved] programmable negative Bias voltage

    Hey Klaus, We got the parts this Monday, The TI Op amp did not work out, It has a lot of chopper noise. I ended up used the op amp from ST (TSZ121)...
  12. Z

    ADC voltage/current sensing

    Hi Everyone, I am trying to use MSP432 on chip 14 bit ADC to sense output from a current sensing op-amp(https://datasheets.maximintegrated.com/en/ds/MAX44284.pdf). I am getting a large reading error from my ADC compare to the multimeter reading. My question is Do i need to have a front end...
  13. Z

    Generate Programmable Bias Current, 1uA to 1mA

    Hi Everyone, I am trying to generate a programmable bias current from 1uA to 1mA using the REF102 from TI. Ideally The accuracy should be within 3% error. Here is the example application from the data sheet. I am planning to replace R with a programmable resistor. However, My concern is that...
  14. Z

    [SOLVED] [moved] programmable negative Bias voltage

    Hi KlausST, Thanks for the detailed reply. I picked a Chopper-Stabilized Operational Amplifier from TI. It has ultra low input offset voltage and offset current. https://www.ti.com/product/TLC2652A I also picked a resistor matching network from LT spice. It has 0.01% matching Accuracy and...
  15. Z

    [SOLVED] [moved] programmable negative Bias voltage

    Hi Klasus, Thanks for the reply. Here is the circuit i simulated, as you suggested . I considered resistance mismatch, and offset voltage of the op-amp. I do have some Questions for my complete understanding: 1) What are the consideration for Resistance value selection? My thinking is to...
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