Jing
Junior Member level 1
low offset integrator
I designed an integrator, it is actually a low pass filter, a simple one stage differential amplifier with one terminal input short to the output and connected to a capacitor. In this case, the input is a signal, the output would be the input average voltage. All the transistors work in the weak inversion. The integrator has a tail current of 100pA. The transistor were sized to have a DC offset of 5mV, that means the output is 5mV apart from the input DC level. However, when I tested this integrator, the offset is as large as 50mV. I don't know how come there is such a large DC offset.
The capacitor connected to the output in order for filtering is a MOSCAP. This big MOSCAP (10um by 10um ) was put quite close to the one side of this differential pair. Is it because of this to make the differential pair asymmetrical in the layout, and then cause such a big DC offset? Or is it because the tail current of 100pA is too small, it is comparable to the leakage current in transistors, therefore cause a big DC offset?
I designed an integrator, it is actually a low pass filter, a simple one stage differential amplifier with one terminal input short to the output and connected to a capacitor. In this case, the input is a signal, the output would be the input average voltage. All the transistors work in the weak inversion. The integrator has a tail current of 100pA. The transistor were sized to have a DC offset of 5mV, that means the output is 5mV apart from the input DC level. However, when I tested this integrator, the offset is as large as 50mV. I don't know how come there is such a large DC offset.
The capacitor connected to the output in order for filtering is a MOSCAP. This big MOSCAP (10um by 10um ) was put quite close to the one side of this differential pair. Is it because of this to make the differential pair asymmetrical in the layout, and then cause such a big DC offset? Or is it because the tail current of 100pA is too small, it is comparable to the leakage current in transistors, therefore cause a big DC offset?