A system and method for clocking in analog-to-digital (ADC) converter in a synthetic instrument unit is presented. A method begins by applying an input clock to an amplifier to produce an amplified clock. The amplified clock is filtered to produce a filtered clock. The ADC of this synthetic instrument unit is clocked with the filtered clock. The input frequency of the ADC corresponds to a second or higher order Nyquist zone that is above the sampling frequency of the ADC. The input data is carried by an intermediate frequency (IF) signal. The filtered clock of ADC is switched off a clock path of the ADC when the ADC is not in use.