Hi all,
my graduation project about RFID , and this schematic is concern reader, my problem is the function of every op-amp that concern the receiver part of the reader.......... the picture is attached with my post.
and thank you all.

 

1 - Voltage follower
2 - Inverting amplifier
3 - High pass active filter
4 - Inverting amplifier
5 - Comparator with hysteresis

 

Download this document:
http://www.datasheets.org.uk/indexdl/Datasheet-036/DSA0032356.pdf
Start on page 47 (relative page 51).
The schematic you attached is on page 51 (relative page 55).

 

Download this document:
http://www.datasheets.org.uk/indexdl/Datasheet-036/DSA0032356.pdf
Start on page 47 (relative page 51).
The schematic you attached is on page 51 (relative page 55).

The Microchip schematic shows the LM339MA op-amp with inputs floating. Is that a Bad Thing? I remember reading that unused op-amps should be not have their inputs left unconnected (e.g., configure as voltage follower).

 

LM339's are comparators that have open collector outputs.
The unused inputs should be grounded. The unused outputs can be left disconnected.

 

Has anyone else thought that op-amps and comparators should have different schematic symbols?

 

Well, they actually have a lot of similarities - it's just that they are optimized for their particular functions.

In a limited way, you can use one for the other - at low speeds, and if you don't really care about optimal response.

You'll quite frequently see schematics where someone used 3 of a quad opamp as opamps, and the remaining one as a comparator - or something similar.

A new member posted a schematic of a PWM circuit, and wanted an explanation of how it worked. It used two channels from an LM324; one as an opamp to create a triangle wave, and the other as a comparator. They could have just as well used an LM393 dual comparator. National actually markets an IC that has an opamp for one channel, and a comparator for the other; that would be a good device to use for such circuits.
The LM392 opamp/comparator:
http://www.national.com/ds/LM/LM392.pdf
The opamp is like a channel from an LM158/LM358.
The comparator is like a channel from an LM193/LM393.