DC gain requirement of THA in pipeline ADC

[overmars]

I follow the theory that for a 14-bit ADC, the DC gain of THA should be larger than 100dB to remove the static error. But recently when running the trasient simulation, I found that if changing the DC gain to Av=70dB, the THA output still remains as ideal as the DC gain equals 100dB. But I was also told that the opamp of first stage MDAC shall have higher DC gain than THA.

So why is that? What exactly determine the DC gain for opamp of THA and of MDAC?

Thank you in advance!