Power supply ripple rejection in tuner oscillator stage
View Patent ↗A bipolar transistor (Tr) in an oscillator stage of a tuner is provided with a diode (D 10 ) in series with a resistor (R 11 ) coupled between the base of the transistor (Tr) and the reference voltage to which the emitter of the transistor (Tr) is coupled. The diode (D 10 ) allows a decreased resistor (R 11 ) value which causes the supply voltage ripple (Vr 1 ) on the collector originating from the base to decrease so as to better compensate the supply ripple (Vr 2 ) on the collector directly originating from the supply voltage (Vs.).
1. A method of suppressing supply voltage ripple in an output of a tuner oscillator stage, the tuner oscillator stage comprising:
a transistor having a control electrode, and two electrodes of a main current path,
a first impedance being coupled between the control electrode and a first terminal,
a second impedance being coupled between the control electrode and a second terminal,
a third impedance being coupled between one of the two electrodes of the main current path and the second terminal, and
an element being arranged in series with the second impedance, the element having a low impedance for AC current and a well-defined voltage drop for DC current, the first and the second terminal being arranged to receive a power supply voltage, the method comprising the steps of:
allowing a first ripple occurring in a power supply voltage at the first terminal to be applied to said control electrode of said transistor, whereby said transistor passes said first ripple; and
combining, at an output of said tuner oscillaton stage, said first ripple with a second ripple occurring in a power supply voltage supplied to said main current path, whereby said first ripple and said second ripple have opposite signs and compensate for each other.
2. The method as claimed in claim 1 , wherein the transistor is a bipolar transistor having a base, a collector and an emitter, the first impedance being coupled between the base and the first terminal, the second impedance being coupled between the base and the second terminal, a collector impedance being coupled between the collector and a third terminal, the third impedance being coupled between the emitter and the second terminal, and the element being arranged in series with the second impedance.
3. A method as claimed in claim 1 , wherein the element comprises a diode, which is poled to conduct in operation.