small "dip" in frequency response at about 80 kHz
By the measurements we discovered small "dip" - minus 6 dB - in frequency response at about 80 kHz. simulations shown that the reason was the output impedance of the offset correction circuit. For some range of frequencies, this impedance behaves as a part of feedback of input amplifier, and therefore the gain falls down (what was visible as a "dip"). The offset correction circuit must have been rebuilt. The negative effect of the upgraded design is the degraded noise level (10 bit ENOB, instead 11 bits at the most sensitive range).