Potential use of MOS capacitor in constructing integrators

[threekingtiger]

As is known to all, continuous integrators are widely used in analog modules, such as continous delta-sigma modulators, audio Class D amplifiters' PWM stages, triangular wave generators, etc. The capacitors needed in integrators are mostly MIM cap or PIP cap due to their excellent linearity for signal processing.

My boss asked me if it's possible to switch the process from 2p2m to just 1p2m in our new audio Class D amp design, which means his money saving and my dear PIP capacitor's fareware. The only device which I could use now is the MOSFET as a cap with its DSB terminal connecting together as a whole.

So I'm wondering if there's any possibility to use MOSCAP as the capacitor in the integrator by avoiding its nonlinear C-V characteristics.

 

[erikl]

If you can get along with the +25% non-linearity between ±Vth, you could use anti-parallel MOScaps:

 

[threekingtiger]

Thanks, erikl. I've thought of using anti-parallel structure to ease the non-linearity problem but not so good. What I'm tring to do is maintaing the MOSCAP in strong inversion by controlling the cap's two terminals voltage. But the circuitry used to fulfill this job seems to be very comlicated and might introduce more non-linearity. The worst result is persuading my boss not be that thrift. haha

 

[dick_freebird]

See if you can have a depletion-mode capacitor. The nonlinearity
there will be less. Never as good as a MIM cap though.