Input Offset Voltage and Current in Varicap Diode Modulators

An analytical study about the input offset voltage and current in varicap diode modulators is presented. Some relations for defining their value and their temperature drift are established. Diode selection to minimize the offset voltage and current is considered. Analytical results are proven in an electronic electrometer with a modulator using reverse polarized diodes. With this electrometer a 31 ¿V/°C input offset voltage, a 0.1-pA input offset current and a 0.016 pA/°°C temperature drift are obtained.