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PGA204: PGA Component Selection Assistance

Manyam Abhishek
Prodigy 60 points

Part Number: PGA204
Other Parts Discussed in Thread: PGA848, PGA848EVM, ADS112S14, OPA4197

Dear Team,

We are currently working on an analog front-end design that includes a Programmable Gain Amplifier (PGA), a low-pass filter, and an Analog-to-Digital Converter (ADC) as key components. Hence We request your guidance and support on our component selection and overall design approach. 

PGA Specifications:

1. Voltage protected analog signal received form Input connector will be sent to PGA.

2. PGA should have 2-bit gain control, resulting in 4 pre-determined gains as per requirement mentioned below.

3. PGA must allow user to program the gains of 1,10,100 and 1000 through FPGA programming.

4. Gain is set through A0 and A1 pins controlled through FPGA.

5. Frequency of Operation: 4-12KHz.

6. We have currently identified PGA204 and PGA848 for this application. Kindly confirm if this is suitable for our requirements or suggest alternatives if required.

Low-Pass Filter Specifications:

1. 8th order Butterworth low pass filter to attenuate the frequencies above 30KHz.

Analog to Digital Converter  Specifications:

1. 16-Bit sampling ADC with the maximum speed of operation s up to 12 KHz. With the sampiling frequency of 100KHz.

Input Specifications:

1. Input Voltage range: +/- 10V

2. Input Impedance: 10MOhm

3. Minimum Alias free Bandwidth: 8 KHz

4. Alias rejection: -90 dB

5. Dynamic Range: 80 dB

6. Frequency of Operation: 4-12 KHz.

Kindly let us know for further information.

Best Regards,

Abhishek

  • 0
    TI__Mastermind 24112 points

    Hi Abhishek, 

    Thank you for posting on e2e - I am so sorry for the delay in response (there appears to be a bug in the system in auto-assigning initial threads).

    I agree with the selection of the PGA204 and/or PGA848. 

    If you would like, I recommend using the PGA848 since it is a newer generation device and therefore has an evaluation module: PGA848EVM. 

    It doesn't have the option to go up to 1000 but a post-amp can always be added using an ADC with an internal PGA is an option as well. 
    Since the requirements is for to be set with just two bits, one of the three will have to be hard wired.

    As an example, if A0 is always high, the generated gains are: 

    001 -> 1, 011 -> 5, 101 -> 20, 111 -> 100. 

    If you would like, I can reassign this thread to the ADC team for their suggestions. 

    All the best,
    Carolina

  • 0 in reply to Caro Gomez
    Prodigy 60 points

    Hi Carolina,

    We understand that the PGA204 is a relatively older device and having limited resources compared to the PGA484.

    Could you please elaborate on the use of a post-amplifier stage to achieve an overall gain of 1000. Additionally, we request your recommendations for suitable ADCs with an internal PGA.

    Kindly also reassign this thread to the ADC team for further inputs. Furthermore, please share your comments on the low-pass filter as well.

    Best Regards

    Abhishek

  • 0 in reply to Manyam Abhishek
    TI__Mastermind 24112 points

    Hi Abhishek, 

    There are a number of ADC devices that have an integrated PGAs that can be used in the signal chain with the PGA848.

    For example, the middle pin A1 can be hard wired to be 0, resulting in gains of 0.5, 1, 10, and 20 from the PGA848. The internal PGA of the ADC can be set to a gain of 5 or 50 to achieve the remaining gain of 100 and 1000. 

    Here is a snippet of the ADS112S14 datasheet, which offers both a gain of 5 and 50. 

    As for the 8th order Butterworth filter, I recommend using the filter designer tool: https://webench.ti.com/filter-design-tool/

    Here is an option that I made using the tool: filter-design-report-46.pdf, it uses the OPA4197 as this was a precision amplifier with adequate bandwidth at a reasonable price. 

    I will transfer the thread to the ADC team to confirm my recommendation of the ADS112S14. 

    All the best,
    Carolina

  • 0 in reply to Caro Gomez
    TI__Guru 51270 points

    Hello Abhishek,

    The ADS112S14 will support the desired gain of 1 or 10, but it will not support +/-10V input when PGA gain is set to 1.  You would need to add attenuation between the PGA output and the ADC input, and level shift, to support +/-10V. 

    The ADS112S14 input range is 0V to VREF; and the scaling can be done using the ADS112S14 2.5V reference and 3 resistors.

    Regards,
    Keith Nicholas
    Precision ADC Applications