cdbular
Junior Member level 1
Hello,
I have designed a fully differential folded cascode OTA with SC-CMFB.
I haver tested the circuit using a SC-CMFB network using Verilog-A macromodel switches. And the OTA seems to work very well.
When I replace the switches with transistors the clock injection is so bad that the CMFB voltage never is mantained at a fixed value and the performance of the amplifiers is terrible: low gain, the CM voltage is not the same as the reference value. The common mode open loop gain seems to be as large as the differential gain (~70dB) as well as the Unit gain Bandwidth (>125MHz).
What can I do to improve this desing. What should I do to reduce the effect of the charge injection produced by the CMOS switches. What is the "secret technique".
I have designed a fully differential folded cascode OTA with SC-CMFB.
I haver tested the circuit using a SC-CMFB network using Verilog-A macromodel switches. And the OTA seems to work very well.
When I replace the switches with transistors the clock injection is so bad that the CMFB voltage never is mantained at a fixed value and the performance of the amplifiers is terrible: low gain, the CM voltage is not the same as the reference value. The common mode open loop gain seems to be as large as the differential gain (~70dB) as well as the Unit gain Bandwidth (>125MHz).
What can I do to improve this desing. What should I do to reduce the effect of the charge injection produced by the CMOS switches. What is the "secret technique".