| 摘要 |
PURPOSE:To obtain a high-accuracy modulation-type DC amplifier featuring an extremely small offset by securing a special relation for the driving frequency of the first chopper against the noise of the frequency put into the input and obtaining a coincidence of the phase between the driving signal of the first chopper and the noise of the frequency. CONSTITUTION:The modulation-type DC amplifier contains the following component units: first chopper CH1 which receives supply of the DC input signal and is driven at frequency f1; second chopper CH2 which is connected to the step next to CH1 and driven at frequency f2; AC amplifier A which amplifies the output isgnal CH2; synchronous rectifier circuit SR which rectifies the output signal synchronizing with the driving signals of CH1 and CH2; and smoothing circuit SC which smoothes the output signal. In this DC amplifier, driving frequency f1 of CH1 is set to secure f1=fn/2N (N: a positive integer) against the noise of frequency fn which is put into the input. And the phase of the driving signal of CH1 is made indentical to the phase of the noise of frequency fn. In this way, a high-accuracy modulation-type DC amplifier can be obtained with an extremely small offset. |
