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Need Clarification on PGA281AIPW interface with Spartan-6 FPGA

Other Parts Discussed in Thread: PGA281, PGA206, PGA207, PGA204, PGA205, PGA202, PGA203

We are using PGA(Programmable Gain Amplifier) - PGA281AIPW in one of our projects.

We have got couple of questions here with the hardware connectivity.

Question 1:

We have connected a Xilinx Spartan 6 FPGA to the PGA. FPGA will drive the pins (G0(7), G1(6), G2(5),G3(4),G4(3)) respectively.
We have connected VSOP(Pin 11) to +5V, and VSON(Pin 12) to -5V respectively. In this specific case,
Will the PGA work fine with the signals(0s and 1s) driven from FPGA?.If yes, how?

Question 2:

The output from PGA281AIPW is bipolar(VOP(pin9) and VON(pin8)), which inturn feeds a differential ADC(Analog to Digital Converter). We haven't provided any specific
ground pin for PGA281AIPW. Can you please advice how to handle ground in this specific scenario?

Note that we have connected VOCM(pin 10) to ground. But we need to make sure if this design will be fine.

Please advice.



  • Hello Sakthi,

    Please find the answers to your questions below:

    1.)  There will be some issues when operating the product in this manner.  First, the recommended supply voltage for the output stage supply (VSOP - VSON) is +2.7V - +5.5V and you are operating the product with a +10V output stage supply. While the maximum upper and lower voltage limits for the output stage supply support this range, the product performance will not meet the datasheet specifications when operated outside of the recommended supply range (+2.7V - +5.5V). 

    Second, the digital inputs (G0:G4) high and low logic levels are based on the voltage difference between the DVDD supply pin and the VSON pin.  The allowable range of DVDD voltages are (VSON + 2.7V) - (VSON + 5.5V).  Therefore, with VSON connected to -5V the allowable range of DVDD voltages is -2.3V - 0.5V.  This will prevent a GND referenced FPGA from directly communicating with the PGA281 without some type of level translator that will take the 0-3.3V (or other level) output of the FPGA and convert it to a signal biased to -5V.  You will also have to find a way to generate a valid supply voltage for the DVDD supply pin (-2.3V - 0.5V).

    2.) The PGA281 differential output signals are centered around the VOCM voltage.  So, as long as the ADC and PGA share a common voltage potential through the VOCM pin then there won't be any grounding or biasing issues.

    I also have a few questions for you.

    1.)  What VSP and VSN voltages are you applying to the PGA281?

    2.)  What are the ADC supply voltages and what is the input voltage range of the PGA?

  • Hello Collins,

    Thanks for your reply.

    Please find the answers to your questions:

    1. We are applying VSP(+15V) and VSN(-15V) respectively.

    2. PGA input range is +10V to -10V(20Vpp)

    We have decided not to use PGA281 since it is not meeting our requirment.

    In our project, the required peak to peak output from PGA is 10Vpp. Please suggest any PGA which suites for the requirement as listed below.

    1.Input = +10V to -10V which is 20Vpp.
    2. Output range = 20Vpp or 10Vpp.

    Would appreciate your inputs.

  • Hello Sakthi,

    There are several PGA options that may meet your requirements. Unfortunately none of the options have as many gain steps as the PGA281, but perhaps you'll find one that includes the gains and bandwidths your system is requiring.

    Take a look at the: PGA202, PGA203, PGA204, PGA205, PGA206, and PGA207 devices.