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.
Hello TI,
I want to measure signal in range of hundreds of nV to hundreds of uV, the sensor is piezo disc which may or may not have DC offset, the signal would be sinusoidal or complex signal with various frequency components. My frequency range is 3KHz to 14KHz. Another requirement that have is i should be able to program the gain in 1 dB steps. The output of this amp will be filtered and connected to ADC. My supply voltage requriements are 3.3V or 5V. Please suggest a similar part with 1 dB steps, and ideally i would like to have preamp in built.
Hello Sumeet,
I would suggest a precision amplifier as the first stage and the second stage as the programmable or variable gain amplifier in which you would vary the gain at 1dB steps or less. Would your design be able to handle a two stage amplifier, or is size a concern or constraint for your design?
Also what is your supply voltage requirements, and what is the output voltage range as well as what will this amplifier be driving? As in what is the load or will this be interfacing an ADC. If interfacing an ADC, do you need a differential or single ended output?
Thank you,
Sima
Hi Sima,
Yes, design would be able to handle two stage amplifiers, ideally supply voltage is 3.3 V is desirable. The output of programable amplifier will be connected to ADC, I would prefer differential amplifier to reduce the common mode voltages. Please suggest me suitable parts for preamp and PGA with variable gain, preferably with attenuators so that voltage at ADC remains in the range.
Hello Sumeet,
For the second stage VGA/PGA, I would recommend either the LMH6518 or PGA870 which have a wide gain range that includes attenuation and a fully differential output to drive an ADC and reduce the common-mode error and distortion as you mentioned. However, LMH6518 has 2dB steps, while PGA870 has 0.5dB steps. Also, these devices operate at 5V. We do have devices that operate at 3.3V, but they are not within the specifications for your design.
Here is a link of the comparison. You can click on each device to look into their datasheets. Also, here is a PGA/VGA device list if you would like to look at our different devices and filter it a different way: https://www.ti.com/amplifier-circuit/pga-vga/products.html#.
For the preamp stage, I am moving this thread to our precision amplifier group which would be able to suggest a precise device that can realize an input that is at hundreds of nV. They should be able to get back to you with recommendations after the weekend.
Thank you,
Sima
Hi Sumeet,
This seems similar to (or is?) an audio transducer. For 1 dB attenuation variation PGAs that are separate from the ADC, we have PGA2500 and PGA4311. Our latest PGA (PGA855) has great performance but fewer gain steps. Newer ADCs such as the TLV320adc5140 have integrated PGAs.
Let me know if you want to pursue a separate gain stage with the devices mentioned above or look more at the integrated ADC solution. I'll have to move this post over to the ADC team if you want more information with the integrated PGA/ADC solution.
Regards,
Mike
Hi Michael,
Since the signal from audio transducers are too low and faint, I will need a preamp with noise performance of less than or equal to 1 nV/sqrt Hz, so i would prefer a preamp with PGA with variable gain stage preferably in 1 dB steps before I send it out to ADC. My input signals are in range of hundreds of nVs and the environment is very noisy, so I think a preamp would be vary preferable.
Hi Sumeet,
I think the best possible solution here for noise would be a JFET front-end followed by a low-noise INA or PGA. Please give us another day to get back to you on this topic while I loop others from the team.
Regards,
Mike
Hey Sumeet,
As Mike mentioned we have an application circuit that uses the JFE2140 followed by the INA849 in a gain of 1000V/V or 60 dB. Here is my app brief:
Best Regards,
Chris Featherstone
My sensing device is piezo disc, please let me know if I use a charge amplifier or something like what you had suggested to me earlier. I intend to connect output of INA849 to PGA870 or PGA855 followed by ADC. But minimum voltage of INA849 is 8 Volts which is a problem for me. can you suggest me a different part? Also, I would need PGA with variable gain that connects to ADC capable of measuring that level of signal. Since the output of INA is single ended, I would need part suggestion that is capable of single ended measurement. JFE + INA849 solutions is promising though.
I also observed that PGA855 has input impedance of 100 G Ohms, would that be better choice? But gain steps are very less.
Do you have any recommendations for low noise charge amplifier?
Hi I used Tina TI to simulate the response of two different topologies;
I used a charge amplifier for piezo disc, below is the attached TINA TI fileRX_chargeAmp.TSC
I also tried to simulate the circuit given by Chris's app note, however I am not getting good output curve, please help:
Please help
Hi Sumeet,
I replied on the other thread.
https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1370751/ina849-ina849
Best Regards,
Chris Featherstone