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PGA309-HT: Should I use a PGA or an opamp amplifier to amplify the analog signal between 10uV and 30mV for gain values between 0 and 1000?

elektroboard
Prodigy 105 points
Part Number: PGA309-HT
Other Parts Discussed in Thread: PGA309, PGA308, INA333

I want to amplify a 10uV-30mV signal for gain values between 0 and 1000. For this process should I use an op-amp based amplifier or a PGA for sensitivity, accuracy, and ability to amplify low-input signals?

  • 0
    TI__Mastermind 22137 points

    Elektroboard,

    The PGA309 is designed for sensor signal conditioning.  It can correct for sensor non-linearity, and adjust gain to compensate for sensor drift.  If you are trying to correct for sensor errors, this is a good device.  As a general amplifier for amplifying a signal, it may not be the best choice.  First, this device is complex and has many features for sensor conditioning.  Second it's overall accuracy for gain, offset, and noise may not be as good as other options.  Also, it requires an EEPROM and must be programed.

    That doesn't mean that you absolutely should not use the PGA309 for general signal conditioning, but it not a typical use case.  Can you give me a little more information on your application?  Is the high temperature range option a key consideration for you?  

    best regards,

    Art

  • 0 in reply to Art Kay
    Prodigy 105 points

    Hi Art.

    I want to use PGA (PGA309 or others) for RTD, Thermocouple, light, O2, humidity sensors with voltage output.

    These PGA devices are suitable such sensor? 

    Some of these sensors need calibration, for instance two-point? Can I use EEPROM for calibration?

    Are PGAs advantageous over opamps for such sensors? What challenges await me?

    Best regards

  • +1 in reply to elektroboard
    TI__Mastermind 22137 points

    Elektroboard,

    1. In general, when you want a reconfigurable flexible circuit for a wide range of different sensors a PGA is a good idea.  Theoretically, you could send a command to the PGA to adjust the gain so that it matches your sensor requirements.
    2. Yes.  You could use the EEPROM to do a two point calibration.  
    3. Comparing PGA309 to op amps, you have the following trade-offs:
      1. Complexity - the pga309 is a complex device with a learning curve.
      2. Analog accuracy - the PGA309 assumes that you are doing a calibration where the errors of the PGA as well as the sensor are combined and eliminated through the calibration process.  Post calibration the total error is low.   However, the gain and offset errors in the PGA309 are eliminated as part of the calibration process.  As such, the PGA309 gain and offset adjustments are not that accurate without calibration 1% to 2%.  If you are calibrating this isn't a major issue.
    4. The PGA308 is similar to the PGA309.  It has the same basic signal path.  The differences:
      1. PGA308 does not calibrate over temperature. 
      2. PGA308 has wider gain, better accuracy, lower noise than the PGA309.
      3. PGA308 uses internal OTP memory (no eeprom).  This is nice because you don't need an extra device, but can only be programed once per bank (limited number of programs).
      4. The PGA308 only has a one-wire interface, whereas the PGA309 has one-wire and I2C.
    5. Both the PGA308 and PGA309 have evaluation modules.  If you are doing calibrations these types of devices may be useful to you.  It would be worthwhile to get an EVM and investigate the device.  Keep in mind that the literature surrounding the devices is focused on bridge sensor signal conditioning and calibration.  Your application is different. 
    6. If you need a PGA with a 5V supply your options are limited.
    7. Rather than an op amp or PGA you may consider an instrumentation amplifier.  An instrumentation amplifier is an amplifier built with three amplifiers with integrated internal resistors.  This can amplifier differential signals and output a single ended signal.  The INA333 is a good example of this.

    I hope this helps.  

    Best regards, Art

  • 0 in reply to Art Kay
    Prodigy 105 points

    Thanks for detailed and quality answers Art. I am goint to a IA.