1212x schematic Question

[amtech2005]

On the other geotech forum , T-Hunting "schematic 1212x pdf " . Whats the 2 overlapped circles represent? On IC U-1 at pins 5 and 1, also U-1 at pins 12 and 16 ?? Thanks Eugene

[Qiaozhi]

On the other geotech forum , T-Hunting "schematic 1212x pdf " . Whats the 2 overlapped circles represent? On IC U-1 at pins 5 and 1, also U-1 at pins 12 and 16 ?? Thanks Eugene

U1 is an OTA (operational transconductance amplifier).
The two overlapping circles indicate that (unlike a conventional opamp) the output is a current source, rather than a voltage. This design is quite similar to a Rimatron 7MX, as it uses OTAs to sample the RX signal instead of the usual analog switches. Pins 1 and 16 are controlling the gain of the output stages. In this design they are used to do the sampling.
The top channel is GEB and the bottom is DISC.

[amtech2005]

1212x schematic question

Thank-you for that information , i dont see that symbol too often , unless a lot of schematics arent properly written or 1212x is one of the few detectors that is designed that way. Im going to look at the IC data sheet for U-1 and see what noise characteristics it has , The only purpose of that chip being used that I can see is a lower signal to noise ratio. Thanks again Qiaozhi. And Happy Holidays to Everyone in this forum. Eugene