Amplitude control device for electrical oscillator and electrical oscillator comprising such a device
View Patent ↗An amplitude control device for a signal output by an oscillator includes a rectification circuit for rectifying the output signal, and a differential amplification circuit for generating a biasing current control signal for the oscillator. The biasing current control signal is based upon the output signal from the rectification circuit and a reference voltage. A dividing bridge and an adder are designed so that only a fraction of the reference voltage is used to define the amplitude of the oscillations. The contribution made to the oscillator phase noise by the reference voltage noise is considerably reduced.
1. An amplitude control device for an output signal from an oscillator, the amplitude control device comprising slaving means comprising:
rectification means for rectifying the output signal;
differential amplification means connected to said rectification means for providing a control signal for controlling an oscillator biasing current;
a voltage divider bridge comprising first, second and third resistances connected together in series between a first voltage reference and a second voltage reference, said voltage divider bridge for dividing the first voltage reference into first and second voltage fractions, the first voltage fraction being taken between said first and second resistances, and the second voltage fraction being taken between said second and third resistances;
an adder for adding the rectified output signal and the second voltage fraction, and providing a summed signal to a second input of said differential amplification means, said adder comprising a fourth resistance having a first terminal connected to said rectification means, and a second terminal connected to said voltage divider bridge for receiving the second voltage fraction; and a fifth resistance having a first terminal connected to said rectification means, and a second terminal connected to said voltage divider bridge for receiving the second voltage fraction;
said rectification means comprising a first bipolar transistor comprising a base connected to the first terminal of said fourth resistance, a collector, and an emitter; and a second bipolar transistor comprising a base connected to the first terminal of said fifth resistance, a collector connected to the collector of said first bipolar transistor, and an emitter connected to the emitter of said first bipolar transistor; and
said differential amplification means comprising
a first P-type MOS transistor comprising a gate, a source connected to the collectors of said first and second bipolar transistors which forms an output of said differential amplification means, and a drain connected to a biasing voltage,
a second P-type MOS transistor comprising a gate connected to the gate of said first P-type MOS transistor, a source connected to the gate of said first P-type MOS transistor, and a drain connected to the drain of said first P-type MOS transistor,
a third bipolar transistor comprising a base connected to said voltage divider bridge for receiving the first voltage fraction, a collector connected to the source of said second P-type MOS transistor, and an emitter connected to the emitters of said first and second bipolar transistors, and
a sixth resistance having a first terminal connected to the emitters of said first, second and third bipolar transistors, and a second terminal connected to the second voltage reference.
2. An amplitude control device according to claim 1 , further comprising:
a first decoupling capacitor having a first terminal connected to the second terminals of said fourth and fifth resistances; and
a second decoupling capacitor having a first terminal connected to the emitters of said first, second and third bipolar transistors, and a second terminal connected to the second voltage reference.
3. An amplitude control device according to claim 1 , further comprising additional slaving means connected to the oscillator for controlling an oscillator noise level for frequencies greater than frequencies within a passband of said slaving means.
4. An amplitude control device according to claim 1 , wherein the oscillator is connected to said differential amplification means for receiving the control signal, the oscillator comprising a current generator for providing the oscillator biasing current, the current generator comprising a resistance, and a transistor connected in series to the resistance, the resistance having a value so that the transistor operates in a resistance zone.
5. A circuit comprising:
an oscillator for providing an output signal; and
an amplitude control device connected to said oscillator for controlling an amplitude of the output signal, said amplitude control device comprising
rectification means for rectifying the output signal,
differential amplification means connected to said rectification means for providing a control signal for controlling an oscillator biasing current,
a voltage divider bridge comprising first, second and third resistances connected together in series between a first voltage reference and a second voltage reference, said voltage divider bridge for dividing the first voltage reference into first and second voltage fractions, the first voltage fraction being taken between said first and second resistances, and the second voltage fraction being taken between said second and third resistances,
an adder for adding the rectified output signal and the second voltage fraction, and providing a summed signal to a second input of said differential amplification means, said adder comprising a fourth resistance having a first terminal connected to said rectification means, and a second terminal connected to said voltage divider bridge for receiving the second voltage fraction; and a fifth resistance having a first terminal connected to said rectification means, and a second terminal connected to said voltage divider bridge for receiving the second voltage fraction,
said rectification means comprising a first bipolar transistor comprising a base connected to the first terminal of said fourth resistance, a collector, and an emitter; and a second bipolar transistor comprising a base connected to the first terminal of said fifth resistance, a collector connected to the collector of said first bipolar transistor, and an emitter connected to the emitter of said first bipolar transistor, and said differential amplification means comprising
a first P-type MOS transistor comprising a gate, a source connected to the collectors of said first and second bipolar transistors which forms an output of said differential amplification means, and a drain connected to a biasing voltage,
a second P-type MOS transistor comprising a gate connected to the gate of said first P-type MOS transistor, a source connected to the gate of said first P-type MOS transistor, and a drain connected to the drain of said first P-type MOS transistor,
a third bipolar transistor comprising a base connected to said voltage divider bridge for receiving the first voltage fraction, a collector connected to the source of said second P-type MOS transistor, and an emitter connected to the emitters of said first and second bipolar transistors, and
a sixth resistance having a first terminal connected to the emitters of said first, second and third bipolar transistors, and a second terminal connected to the second voltage reference.
6. A circuit according to claim 5 , wherein said amplitude control device further comprises:
a first decoupling capacitor having a first terminal connected to the second terminals of said fourth and fifth resistances; and
a second decoupling capacitor having a first terminal connected to the emitters of said first, second and third bipolar transistors, and a second terminal connected to the second voltage reference.
7. A circuit according to claim 5 , further comprising a slaving circuit connected to said oscillator for controlling an oscillator noise level for frequencies greater than frequencies within a passband of said amplitude control device.
8. A circuit according to claim 5 , wherein said oscillator is connected to said differential amplifier for receiving the control signal, said oscillator comprising a current generator for providing the oscillator biasing current, said current generator comprising a resistance, and a transistor connected in series to said resistance, the resistance having a value so that said transistor operates in a resistance zone.