pegasus-215
Newbie level 4
hi, there~
i want to put a high pass fiter between two closed loop amp to act as a DOC (direct current offset cancellation).
in the figuer below, the op point in the input and output ports should be 900mV.
Before the capacitor and the resistors (AC coupling circuit)are put in the circuit, this circuit works well.
As the cap. (1pF) and res.(1M ohm) are put in the circuit, it will change the second closed loop amp's input op point, about 1.79v(i use tsmc0.18, 1.8v technology).
between the two res. in the AC coupling, is a reference voltage, 900mV.
i find if the res. value are set to 500k ohm, the 2nd closed loop amp's input op point will be 900mV. But in this condition, if i want the high pass's cut-off frequency is 1M Hz(my amp's bandwidth is 12M Hz), the cap.'s value should be 17p F.
Is 17p F too large to be accepted?
what other solutions can be found to make the 2nd closed loop amp's input op point is 900mV?
thanks a lot~
i want to put a high pass fiter between two closed loop amp to act as a DOC (direct current offset cancellation).
in the figuer below, the op point in the input and output ports should be 900mV.
Before the capacitor and the resistors (AC coupling circuit)are put in the circuit, this circuit works well.
As the cap. (1pF) and res.(1M ohm) are put in the circuit, it will change the second closed loop amp's input op point, about 1.79v(i use tsmc0.18, 1.8v technology).
between the two res. in the AC coupling, is a reference voltage, 900mV.
i find if the res. value are set to 500k ohm, the 2nd closed loop amp's input op point will be 900mV. But in this condition, if i want the high pass's cut-off frequency is 1M Hz(my amp's bandwidth is 12M Hz), the cap.'s value should be 17p F.
Is 17p F too large to be accepted?
what other solutions can be found to make the 2nd closed loop amp's input op point is 900mV?
thanks a lot~
