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ADS127L01: Is ADS127L01 suitable for both static and dynamic strain gauge measurement?

TICL
Prodigy 160 points
Part Number: ADS127L01
Other Parts Discussed in Thread: ADS124S08, ADS1261, , ADS127L11, , THS4551

We are designing a strain gauge based sensing circuit and need to make both static (signal unchanged or slowly changing around 30-60 seconds) and dynamic (signal vibrates around ~1kHz) measurement as accurate as possible.  The entire circuit is currently designed to be powered by a 3.3V battery so that limits my options for the ADC.   I am aware of the more integrated solution such as ADS124S08 (only 4-kSPS) and ADS1261 (only 40-kSPS) but their sampling rate won't resolve my 1kHz signal changes. I'm drawn into the 512kSPS of ADS127L01 and even at low-power mode it offers up to 128kSPS - so that should take care of my needed sampling rate.   It also operates under 3V so that'll work well with my 3.3V and my LDO.  I'm not sure what could be my trade off for using a high-speed ADC for this application - e.g. does it take away some stability while making static measurement (bad drift over short time)? Is it a good choice for static and dynamic strain gauge or are there better alternatives for low-voltage/battery power supply?

 

  • 0
    TI__Mastermind 36240 points

    Hello,

    The primary tradeoff in using a high-speed delta-sigma verses the lower speed options is the lack of integrated functions such as a PGA, input buffer, voltage reference, and so forth.  At a minimum, you will need to supply an external input amplifier buffer and external voltage reference to use these higher speed ADCs.  These ADCs are optimized for both high speed AC measurements, and also have a chopper stabilized front-end for precision DC measurements.

    I suggest looking at the newest version in this family, the ADS127L11.  This ADC includes input and reference pre-charge buffers, which relax the input amplifier requirements.  The ADS127L11 also has a wide range of digital filter options, is available in a 3x3mm package, and has overall lower power-consumption.  It can be operated from an analog supply voltage as low as 3V typical (2.85V minimum) in low-speed mode, supporting wide-band filter data rates up to 50ksps, and low-latency filter data rates up to 133ksps.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 160 points

    Thanks for the suggestion - I wasn't aware of ADS127L01.  On the TI website, it says ADS127L11 has 400kSPS but can reach maximum 1,000kSPS, whereas ADS127L10 has 512kSPS. Of course these depend on power mode and clock speed, but without digging deep into the datasheet L11/L01 has more of less comparable sampling rate.  What I notice so far though is the newer L11 has slightly lower SNR and require higher analog voltage (2.85-3V) to drive than the older L01.  My signal comes out of an In-Amp so I'm not totally sure how the L11's pre-charge buffer could make any noticeable impact (or do they?).  Do you still think it worth to try out or replace L01 with L11? L01 has been out-of-stock for a really long time but L11 is available so I assume the production of L11 would be more readily available than L01 in coming months?

  • 0 in reply to TICL
    TI__Mastermind 36240 points

    Hello,

    The SNR for the L11 has been improved by allowing use of a higher voltage reference, up to 5V.  However, this requires use of a 5V analog supply.  At lower operating voltages, the noise (and SNR) will be similar between the two ADCs.

    The pre-charge buffers inside the ADS127L11 reduce the average load current by about 99% (depends on exact conditions).  This reduces the bandwidth requirements of the external input amplifier.  If you do not need best-possible THD performance, then you can bias the negative input at 1/2 supply voltage and drive the positive input directly form a single ended amplifier.  If the instrumentation amplifier has sufficient bandwidth, and good output drive, it may be possible to directly drive the ADS127L11 input directly with the INA when using the internal pre-charge buffers.  

    However, to get best performance, the ADC inputs should be driven with a fully differential amplifier.  Both evaluation boards for ADS127L01EVM and ADS127L11EVM use the THS4551 amplifier to meet full ADC performance.  If you use this amplifier to drive the inputs, then you can expect similar performance for either ADC when using a lower voltage reference and a 3V analog supply.

    Right now, we have more inventory for the ADS127L11, so parts are easier to get.  I cannot predict if or for how long this will remain the case.

    Regards,
    Keith