• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 46 subscribers
  • Views 419 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS131E08: We need Op-amp for Signal Conditioning section of 4-Channel ADC card

Lakshmanan V
Intellectual 480 points
Part Number: ADS131E08
Other Parts Discussed in Thread: OPA2325, OPA320, PGA112, PGA2500, ADS131E04, ADS131A04, ADS1274
Hello sir,

We are working on New project called 4-Channel ADC card

Please suggest me relevant part for  following section. The Requirements are

1). Low Noise Amplifier spec.

Voltage Noise : 10 nV/√Hz

Current Noise : 1 fA /√Hz

Very low input bias current

Fixed Gain : 40 dB

2). Charge Amplifier spec.

Voltage Noise : 10 nV/√Hz

Current Noise : 1 fA /√Hz

Very low input bias current

Fixed Gain : 40 dB

3). Programmable Gain Amplifier spec.

Variable gain of 0  to 60 dB with minimum gain step variation 1dB.

Minimum Supply Voltage : ±2.5V

4). Anti-aliasing Filter spec

4 or 8th order Elliptical LPF Filter or Butter-worth LPF Filter with unity gain

Cutoff frequency: 4 kHz

5). 4-Channel 24-bit ADC spec

24-Bit resolution

Support Simultaneously-Sampling

support minimum Sampling rate : 12.8 kHz

Suggest me the op-amp, PGA & 24-Bit ADC relevant part for above specification.

Hereby enclosed our project Block diagram for your reference.

4 channel Data Acquisition Card block diagram.pdf

Note:- Supply Voltage for all op-amp signal conditioning section work with ±2.5V or ±5V

Regards

Lakshmanan V

  • 0
    TI__Guru* 92715 points
    Lakshmanan,


    I would post this question in amplifier forum as well, just to check my answers. In this forum, we primarily deal with just the ADC questions that come up and you might want recommendations from someone that has more experience with the amplifier devices from TI. The amplifier forum can be found with the link below:

    e2e.ti.com/.../14

    Regardless, here's a set of answers that I came up with.

    1. and 2. I'm not sure what other specifications you'll need out of the amplifier, but with such a low input current noise, you'll need something that is either low for the JFET amplifiers, or something that is CMOS. I think that the OPA320 and OPA2325 devices are close to, or meet the specifications that you need.

    3. There are only a few PGA devices that operate on such a low supply. I think that one would be the PGA11x set of devices (search for PGA112). However, these devices have limited gain settings and are not meant to operate with a bipolar supply (as the digital inputs are voltages with respect to ground. The other device that I could think of that was even close is for a microphone pre-amplifier. If you look up the PGA2500, you can read about it, but I'm not sure it works for your application. It does have 1dB gain steps, with missing steps between 0 and 10dB, and the supplies run on ±5V.

    4. I don't think TI has any specific filters, and I don't know of any specific designs for this type of filtering.

    5. There are several devices that have this data rate, I think the ADS131E04 is fine, but there are probably more specifications that you might be concerned with. Based on data rate, here is a list of devices that might work.
    ADS131E04
    ADS131A04
    ADS1274

    However, you should be aware that as the data rate goes higher, the noise increases. At higher data rates, you will not get the equivalent of 24 bits of resolution because of the noise. Read through the datasheets and determine the data rate and noise that is acceptable.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Intellectual 480 points

    Hello sir,

             We have plan to use Programmable gain amplifier part PGA2500.

    Ana also we plan to use ADC part: ADS131E04.

    Whether PGA2500 can directly drive ADS131E04 ?.

    Regards

    Lakshmanan V

  • 0 in reply to Lakshmanan V
    TI__Guru* 92715 points

    Lakshmanan,


    I know of the PGA2500 and I've looked at it, but only for audio applications. Based on the specifications on the ADS131E04 and the PGA2500, it looks like the two could work together, including some filtering mentioned in the PGA2500 datasheet.

    Again, I've really only seen the PGA2500 in audio applications, specifically as a microphone pre-amplifier. I believe that the input impedance is rather low because of the structure of the common-mode input servo.



    Joseph Wu

  • 0 in reply to Joseph Wu
    Intellectual 480 points

    Hello sir,

                 We decide to use PGA2500 in this project.

    In Datasheet mentioned that Quiescent current of PGA2500 is ± 40mA at ±5 Volts rail.

    While working time what is the maximum supply current consumed by PGA2500 at  ±5 Volts rail?.

    Regards

    Lakshmanan V

  • 0 in reply to Lakshmanan V
    TI__Guru* 92715 points

    Lakshmanan,

    I think you've already posted this into the Audio Forum, and I would consider them the best source of information. However, I believe that based on the datasheet, the PGA2500 max current is ±40mA, while the typical current is ±30mA both are during normal operation.

    I generally support ADC products, while the Audio Forum would support the PGA2500.

    Joseph Wu