# Voltage follows and INA146 (precision difference amplifier)

Discussion in 'Audio' started by ajnElecPnt, Oct 3, 2018.

1. ### ajnElecPnt

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0
Oct 3, 2018
I planing to use an INA146 precision difference amplifier to do voltage level conversion from 0-12v to 0-3.3volt.
Since the input should be possible to change I like to add voltage follower on the input of the INA146.

My question is what kind of OP-amp should I select that are not damage the performance of the INA146. I guess that it is important that I use device with dual op:s so they are as equal as possible.

What other parameter should I lock at when I select the OP:s. (Gain, Offset, ...). Need to keep the cost down as much as possible but the performance of the INA146 should not be ruined.

Note:
I planning to power the INA146 with a +-15v supply (or may be +-12v).

Has any one added a capacitor to INA146 and created a 2:nd order LP-filter. If that is the case, should the cut of frequency be set to the same for the first and second stage? There is an example for AD628 that do this.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,296
2,736
Jan 21, 2010
Please post a schematic of the circuit you intend to use.

Presumably, if you can attenuate the input signal to your differential amplifier you can get a signal in the range you want.

3. ### ajnElecPnt

3
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Oct 3, 2018
The input load is just a potentiometer which is moved mechanically relatively quickly (few ms from 0 to max voltage). The problem is that the load/potentiometer will be changed on regular basis so that both voltage and resistance will vary within reasonable limits.

To limit the problem as much as possible I like to add a voltage follower at the input of the INA146. I have no problem with the voltage level conversion. I have calculated the resistor values and it work just fine i pSpice.

The problem is that INA146 has very good performance (common mode, ...) since it has matching resistors on the inputs. So the question is what more parameters (noise, offset bias, slew rate, unit gain stability---) should I check, when I select op-amps as voltage follows in front of INA146? Noise is very important since I need detect standby levels. (the 3.3v ADC is 10 bits right now but may be changed to 12 bits).

4. ### WHONOES

774
168
May 20, 2017
Why do you need voltage followers in front of your INA146?

5. ### ajnElecPnt

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Oct 3, 2018
The problem is solved, but for the record. Several different potentiometers will be used, and changed on regular basis.

Since I did not know the range of the resistance, I thought it should be nice to use a voltage followers. In the end this was not necessary.