I found an interesting schematic here http://cds.linear.com/docs/en/application-note/an87f.pdf . It is fig. 84 Cascode Power Amplifier.
I made a PCB for this schematic and I started to test it. I solder all components on the PCB. When I test something new I like to do it part by part. So I connect +-15V (from laboratory power supply) direct to the OP AMP (without using high voltage supply). With oscilloscope all AC setting looks good, but the problem is that there is a quite large offset voltage in the output. All test are without load.
When I switch on power supply, the offset in the first moment is around -2V (package temperature is 26 °C) and after 2 minute it goes to +0.6V (package temperature is around 60°C).
Is it normal and how can I fix it? I need offset voltage drift less than 1mV (10mV drift is also can be acceptable).
I am developing piezodriver for AFM scanner. I need from +150V to -40V, 1kHz triangle wave at 1uF capacitive load. I need also from low DC drift and low noise. Can you offer me a solution?