i have designded a circuit as the figure shows, VI is the input signal, when S1 is closed, VI transfers to Va, then to Vb through the buffer, when S2 is closed, the signal transfered to VO. the buffer is as the figure shows also, it is a two stage opamp with miller compensation, the period of S2 is 10MHz, the DC gain of the opamp is 86dB, GBW is 72MHz, then, my question is: when CTRL (that is S2) goes high, the signal VO has a jump of 50mV or so, however, when CTRL is always high (that is, the opamp works all the time), and when S2 is closed (that is, goes high), the jump is very small, less than 0.2mV. why? what is the reason? how to solve this problem? please help me, thanks all in advance.