The classic chopper OpAmp was the ICL 7650, and its brother 7652.
It was/is manufactured by Intersil, then by Maxim, and by Linear Technology.
Both have a chopping frequency of 200 or 400Hz.
The 7650 has a low bias current of 1.5pA (typ.), but high noise of 2µVpp (10Hz), wheras the 7652 has a higher bias of 15pA (typ.), but only 0.7Vpp noise.
bias and noise are the complementary parameters of chopper amplifiers, that is the case also for this comparison.
Please also read in the AoE the description about the HP34420A front end, which is extremely low noise, due to its huge area FET amplifier, but has many nA bias current, which has to be compensated to < 50pA by an external circuit.
Nowadays, I find it difficult to find low bias choppers (around a few pA), most have low noise instead.
Therefore I still use these old designs, or the also old LTC1052.
Frank