US 5,418,497 AGranted

Low voltage VCO having two oscillator circuits of different frequencies

AssigneeMotorola, Inc.

InventorFrederick L. Martin

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Abstract

BiCMOS technology is used in the design of a VCO (200) to improve low DC operation. The VCO (200) includes two coupled oscillator circuits (201,219) tuned to different fixed frequencies such that the oscillator resonant frequencies define the tuning range of the VCO (200). The oscillator circuits (201, 219) are coupled such that the frequency of oscillation of the VCO (200) is adjustable via variable resistors (206, 214) by manipulating the bias currents to the two oscillator circuits (201,219). A biasing circuit (208) along with variable resistors (206 and 214) provide the DC bias to the oscillator circuits (201 and 219). The biasing circuit (208) maintains the sum of the biasing currents to the oscillator circuits constant. The oscillator circuits (201, and 219) are interconnected utilizing an RF coupling circuit (211). The VCO (200) is capable of operating at voltages as low as 1.8 volts DC.

Claims16

Dependent claims

A low-voltage Voltage Controlled Oscillator (VCO), comprising:

a first oscillator having a first frequency of oscillation and a first bias current, comprising:
a first frequency resonant circuit;
a first amplifier stage having at least one transistor with a first gain, the first gain of the amplifier is adjusted via a first voltage;
a first feedback path coupled between the first frequency resonant circuit and the first amplifier stage to provide for oscillation;
a second oscillator having a second frequency of oscillation different from the first frequency and a second bias current, comprising:
a second frequency resonant circuit;
a second amplifier stage having at least one transistor with a second gain, the second gain is adjusted via a second voltage;
a second feedback path coupled between the second frequency resonant circuit and the second amplifier stage to provide for oscillation;
a Radio Frequency (RF) coupling circuit for coupling the first and second oscillators so as to produce the operating frequency of the VCO, comprising:
a first coupler for coupling the first frequency resonant circuit to the second amplifier stage;
a second coupler for coupling the second frequency resonant circuit to the first amplifier stage;
an adjustable biasing means, comprising:
means for generating a plurality of DC currents having a fixed sum, the means for generating is coupled to the first and second oscillators via degenerate resistors;
and
means for manipulating the plurality of DC currents between the first and the second amplifier stages to adjust the operating frequency of the VCO.

12 more elements

A VCO adapted for operation with very low supply voltage, comprising:

a DC voltage supply input;
a first oscillator circuit having a first frequency resonant circuit for generating a first radio frequency signal, the first oscillator circuit is directly connected to the DC voltage supply input;
a second oscillator circuit having a second frequency resonant circuit for generating a second radio frequency signal, the second oscillator circuit is directly connected to the DC voltage supply input;
a first amplifier for amplifying the first radio frequency signal, the first amplifier is coupled to the DC voltage supply input through the first oscillator circuit;
a second amplifier for amplifying the second radio frequency signal, the second amplifier is coupled to the DC voltage supply input through the second oscillator circuit;
an adjustable biasing means comprising:
a first adjustable resistor for setting bias current for the first oscillator circuit, the adjustable resistor circuit is coupled to the DC voltage supply input through the first amplifier;
a second adjustable resistor for setting bias current for the second oscillator circuit, the adjustable resistor circuit is coupled to the DC voltage supply input through the second amplifier;
means for generating a plurality of DC currents having a fixed sum, the means for generating is coupled to the DC voltage supply input in parallel with the first and second amplifiers so as to limit the drop of DC voltage available at the DC voltage supply input;
a Radio Frequency (RF) coupling circuit for coupling the first and second oscillator circuits so as to produce the operating frequency of the VCO, comprising:
a first coupler for coupling the first frequency resonant circuit to the second amplifier;
and
a second coupler for coupling the second frequency resonant circuit to the first amplifier.

10 more elements

A communication device, comprising:

a receiver for receiving a radio frequency signal, the receiver including a low voltage VCO, the VCO comprising:
a DC voltage supply input;
a first oscillator circuit for generating a first radio frequency signal, the first oscillator circuit is directly connected to the DC voltage supply input;
a second oscillator circuit for generating a second radio frequency signal, the second oscillator circuit is directly connected to the DC voltage supply input;
a first amplifier for amplifying the first radio frequency signal, the first amplifier is coupled to the DC voltage supply input through the first oscillator circuit;
a second amplifier for amplifying the second radio frequency signal, the second amplifier is coupled to the DC voltage supply input through the second oscillator circuit;
an adjustable biasing means comprising:
a first adjustable resistor for setting bias current for the first oscillator circuit, the adjustable resistor circuit is coupled to the DC voltage supply input through the first amplifier;
a second adjustable resistor for setting bias current for the second oscillator circuit, the adjustable resistor circuit is coupled to the DC voltage supply input through the second amplifier;
means for generating a plurality of DC bias currents having a fixed sum, the means for generating is coupled to the DC voltage supply input in parallel with the first and second amplifiers so as to limit the drop of DC voltage available at the DC voltage supply input;
a Radio Frequency (RF) coupling circuit for coupling the first and second oscillator circuits so as to produce the operating frequency of the VCO, comprising:
a first coupler for coupling the first oscillator circuit to the second amplifier;
and
a second coupler for coupling the second oscillator circuit to the first amplifier.

11 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/270,624Filed 5 Jul 1994
Granted: 23 May 1995
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

H03B 5/1231
Active element in amplifier being semiconductor device: the amplifier comprising one or more bipolar transistors
H03B 5/1209
Using multiple transistors for amplification: the amplifier having two current paths operating in a differential manner and a current source or…
H03B 5/1225
Using multiple transistors for amplification: the generator comprising multiple amplifiers connected in parallel
H03B 5/1243
The means comprising a voltage dependent capacitance: the means comprising voltage variable capacitance diodes