please help me choose an opamp

[JohnKElectroTech]

Hello,

I want to apply a differential amplifier to a passive infrared sensor (PIR). The mean of the PIR output is about 0.7V and signal frequency I want to detect is around 1 - 10 Hz. Is it practical to find an opamp where I can get a gain on the order of 10^4 and input current on the order of 1uA / channel? If you can't recommend a specific opamp, what characteristics should I look for? I thought that I should look for a gain bandwidth product (GBP) / 10 Hz > 10^4, but the opamps in the electronics catalogs I've seen often times don't list the GBP and it's not searchable.

Thanks in advance.

 

[crutschow]

So you want amplify a small AC signal riding on the 0.7V DC?

For a gain of 10^4 and a maximum 10Hz signal you want a GBW of at least 10^4 * 10 or 10^5, but most op amps have a GBW higher than that.

What power supply(s) do you have and what signal output level do you need?

If you have the part number of an op amp then you can find the data sheet with Google. If the electronics catalogs don't list the part number then you shouldn't buy from them.

 

[JohnKElectroTech]

Thanks, crutschow. I found what I was looking for by looking through a few other online catalogs and found a catalog that was searchable by GBP. That's right - it's a small AC signal on a 0.7V DC with a signal output level of about 1 V and a power supply of 5V.

Have you heard of a company called "Microchip Technology"? Are they reliable, or are opamps generally reliable regardless of the manufacturer? Thanks.

 

[crutschow]

If you have a single 5V supply, then you will need an op amp that can operate at that voltage and has a "rail-to-rail" input and output such as this.

Microchip is fine. They also happen to make several million microprocessors a year. Just about any other company that makes op amps is okay also, such as TI, Analog Devices, National Semiconductor, Linear Technology, etc.