VHF varactor for VCO and filter tuning
The BB172X is a single VHF varactor diode in a SOD-323 surface-mount package, designed for voltage-controlled oscillator (VCO) and filter tuning applications where a predictable capacitance-versus-voltage characteristic is needed. Its capacitance ratio of 15 gives a tuning range that covers VHF bands without needing a multi-diode stack, simplifying the bias network and board layout. With a peak reverse voltage rating of 32 V, the diode supports tuning voltages up to that level, which sets the upper frequency limit in the LC tank.
Capacitance ratio and tuning range — what matters for the VCO
The capacitance ratio is measured as the capacitance at 1 V reverse bias divided by the capacitance at 28 V reverse bias, both at 1 MHz. A ratio of 15 means the diode can vary its capacitance by a factor of 15 over that bias range, which directly translates to the frequency tuning range of the resonant circuit. The capacitance at 28 V is 2.754 pF.