subtracting amplifier error

[michal777]

Hi,

348R || 0p8 between pin3(-) of subtracting amplifier and GND must not be there - it doesn't belong to a proper 1x subtracting amplifier circuit and it degrades CMRR.

I guess the bandwidth is not as advertised with the 1GHz op-amp, simply too little gain at 250MHz. I tried some simulations, I'm not sure about the results (had some issues with simulation models) but it seems more like <100MHz.

btw, annotated pdf schematic and pdf of layout would be convenient.

[i3luefire]

348R || 0p8 between pin3(-) of subtracting amplifier and GND must not be there - it doesn't belong to a proper 1x subtracting amplifier circuit and it degrades CMRR.

I guess the bandwidth is not as advertised with the 1GHz op-amp, simply too little gain at 250MHz. I tried some simulations, I'm not sure about the results (had some issues with simulation models) but it seems more like <100MHz.

btw, annotated pdf schematic and pdf of layout would be convenient.

I agree about the annotated schematic and layout pdfs.
But which resistor are you talking about?
I am not really sure I understand that comment.

[michal777]

[ProstetnikJeltz]

Hello, I guess the numbering of the Op-Amps is wrong in the schematics - and maybe on the PCB too.
According to the Datasheet PIN1 is FB, 2 -IN, 3 +IN , 4 -VS ... .
There are diodes (BAS316,115; D1...4) at the PCB and in the BOM, but not in the schematics.