Patent ID: 6559706
Filing Date: 2003-05-06
Classification: H03D

Abstract:
A method of operating mixer circuitry, the mixer circuitry comprising a series circuit of the collector-emitter paths of first-third bipolar transistors, said first transistor having a collector forming one end of said circuit, the emitter of said second transistor being connected to the collector of said third transistor so that the collector voltage of said third transistor corresponds to the emitter voltage of the second transistor and said third transistor having an emitter forming a second end of said circuit, said series circuit being connected at said one end thereof via a first resistor to a supply potential and at said second thereof via a second resistor to a reference voltage, the method comprising:providing a voltage drop across the first resistor, whereby said collector of said first transistor is at a potential between said supply potential and said reference voltage; selecting a varying base voltage for application to a base of said first transistor, said base voltage having a maximum at least equal to said supply potential, being selected to provide a base-collector voltage at which conduction of the base-collector diode does not occur and having a minimum corresponding to a minimum voltage of said collector voltage of the second transistor; providing a mixing base voltage to said second transistor, said mixing base voltage being selected to have a maximum level greater than the minimum collector voltage of said second transistor but less than a voltage at which the base-collector diode conducts, when the collector voltage is minimum, whereby the potential across said series circuit is less than three base-emitter voltages.