PGA does not use reference | Cypress Semiconductor
PGA does not use reference
In a PSoC 3 design I need a differential amplifier but it does not seem to work.
I created a simpler design for the CY8CKIT-030 (as attached):
Two voltage VDACs drive the two inputs of a PGA the output of the PGA can be observed through
a voltmeter and the ADC.
I can control the VDACs and PGA settings through USB.
I checked the settings of the PGAs (PGA_1 in the schematic is implemented by SC0 as seen by the chip so the
relevant registers are 0x5800 pp):
'0x0c', '0x2e', '0x01', '0x00'
So the GNDREF - field in SC0_CR2 is 0, which -- according to the register TRM means the external input is used.
And still, the output of my circuit depends only on the voltage of VDAC8_1, i.e. the positive input of the PGA.
The output is as if the reference input was at 0.
I also checked the analog routing representation and this seems to be correct, the output of SC2 goes to the input of SC0.
I did not find many examples that use the PGA, but maybe someone in the forum has more experience with them.
If not, I need to open a case, I guess.