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/etc... Amplifiers & Other Linear Forum
Help selecting an appropriate differential amplifier
I've been trying out some different types of amplifiers for my application where I need to amplify a differential signal. Originally, I tried an instrumentation amp, but this proved to be too bulky with resistors and all for setting gains (I need to use a TSSOP package size with 2 circuits). Size is one of the biggest constraints because I will be soldering in free space, not on a circuit board. I next tried THS4522 which is low-power differential amp. I'm not too concerned about low-power, but I don't want dual output. I'm looking for a chip that has 2 circuits, each of which take the difference of two inputs and provide only one output. My preference is a fixed gain amplifier, that doesn't necessarily have to be that big (it could even be unity gain). Any help selecting an appropriate chip would be greatly appreciated.
The description you have provided in this line isn't completely clear, "I'm looking for a chip that has 2 circuits, each of which take the difference of two inputs and provide only one output.."
That sounds like you are describing two difference amplifiers, or a dual instrumentation amplifier, but the "only one output" is the unclear part.
PA - Linear Applications Engineering
So the current differential amplifier I have THS4522 is a 16 pin TSSOP chip. It takes 2 input voltages, finds the difference, and then outputs as two signals around a common voltage. I've read that I can just ground one of the output channels so I only have one output voltage, but this results in a half gain. I was curious if there were differential amplifiers that take 2 inputs and only give one output. If this would require an instrumentation amplifier, are there versions of instrumentation amplifiers with fixed gains (so I don't need to place extra resistors across pins, and may actually be able to reduce the number of pins on the chip to less than 16)? The instrumentation amplifier I had used before was the INA2321. I liked this chip because it had single outputs to two input voltages, but it became too bulky when wiring the resistors needed to set the gains. Does anything like this with a fixed internal gain exist? Again, I'd want a chip that does this entire process twice on the chip (two separate channels for conversion of a two input difference to a single output).
It's not clear from your description whether you need two instrumentation amplifiers or just one. The single version of the INA2321 gives you two input terminals and a single output. The gain is 5 without external resistors.
The INA141 (and its dual version, the INA2141) can be set for a gain of 10 or 100 with pin connections (no resistors). You have not mentioned your power supply requirements. The INA141 is best operated from a dual (+/-) supply.
OK, so it seems that INA2321 was actually my best option to begin with. I am not constrained by power supply requirements, I can make most whatever work. As far as implementation of INA2321, at a gain of 5, I don't need any resistors, but I need to wire each RG to its respective V_out? Also, do I leave the refs open or grounded? If I'm not concerned about any shutdown features, should I leave shutdown open or grounded?
Referring to figure 1 in the data sheet: Both shutdown pins should be connected to the V+ power supply. Both RG terminals should be connected to their respective output terminal. (Keep these connections separate for each channel.) R1 is not used. Each REF terminal should be connected to ground, or to the voltage to which you want to reference the output.
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