CMOS voltage controlled phase shift oscillator
AssigneeMicron Technology, Inc.
InventorLeonard Forbes
Life of this patent
Estimating the term…
Abstract
Structures and methods for CMOS voltage controlled phase shift oscillators are provided. The CMOS voltage controlled phase shift oscillators, or phase shift circuit, includes any odd number of stages coupled in series. Each stage includes a CMOS amplifier. A phase shift network is coupled to the CMOS amplifier. The CMOS amplifier provides a gain and allows a small phase shift in each stage to eventually provide a signal which is 180 degrees out of phase with the input signal. In the CMOS amplifier, the PMOS transistor is a diode connected PMOS transistor which acts as a low valued load resistance. In the phase shift network, an NMOS transistor is used as a voltage variable resistor for providing a resistance value in the circuit.
Claims84
A CMOS phase shift oscillator, comprising:
- a number of stages coupled in series between an input and an output, wherein each stage includes:
- a CMOS amplifier;
- and
- a phase shift network coupled to the CMOS amplifier;
- and
- wherein the CMOS amplifier provides a gain and allows a small phase shift in each stage to provide an output signal at the output which is 180 degrees out of phase with an input signal at the input.
A CMOS phase shift oscillator, comprising:
- at least five stages coupled between an input and an output of the oscillator, wherein each stage includes:
- a CMOS amplifier;
- and
- a phase shift network coupled to the CMOS amplifier;
- and
- wherein a phase shift in each stage contributes to a total phase shift, and wherein a small phase shift is realized in each stage at a high frequency such that the at least five stages result in a high oscillation frequency.
A phase shift network, comprising:
- a number of stages coupled in series between an input and an output of the network, the output coupled to the input via a feedback line, wherein each stage includes:
- an amplifier, wherein the amplifier includes:
- an NMOS transistor;
- and
- a diode connected PMOS transistor acting as a load resistor, wherein the diode connected PMOS transistor has a low impedance, RL;
- and
- an NMOS transistor in a phase shift network, the NMOS transistor serving as a voltage variable resistor coupled to the amplifier;
- and
- wherein the amplifier provides a gain and allows a small phase shift in each stage to eventually provide a signal which is 180 degrees out of phase with the input signal.
A phase shift oscillator, comprising:
- a number of stages coupled in series between an input and an output of the oscillator, the output coupled to the input via a feedback line, wherein each stage includes:
- an amplifier, wherein the amplifier includes:
- an NMOS transistor;
- and
- a diode connected PMOS transistor acting as a load resistor, wherein the diode connected PMOS transistor has a low impedance;
- and
- an NMOS transistor serving as a voltage variable resistor coupled to the amplifier;
- and
- wherein the amplifier provides a gain and allows a small phase shift in each stage to eventually provide an output signal at the output which is 180 degrees out of phase with an input signal received at the input, and wherein an oscillation frequency, fo, for the oscillator is defined as fo n/(2×pi×pi×R×C) Hz, wherein pi=3.14 radians, wherein R is a resistance value of the NMOS transistor serving as a voltage variable resistor, and wherein C is a capacitance value provide by the NMOS transistor serving as a voltage variable resistor.
A phase shift circuit, comprising:
- a number of stages coupled in series between an input and an output of the circuit, the output coupled to the input via a feedback line, wherein each stage includes:
- a CMOS amplifier;
- and
- an NMOS transistor serving as a voltage variable resistor, R, coupled to the CMOS amplifier;
- and
- wherein an oscillation frequency, fo, for the circuit increases with the number of stages, and wherein the oscillation frequency increases as an R-C time constant decreases, wherein C is an input capacitance provided by the NMOS transistor.
A phase shift network, comprising:
- a number of stages coupled in series between an input and an output of the network, the output coupled to the input via a feedback line, wherein each stage includes:
- a CMOS amplifier;
- and
- an NMOS transistor, serving as a voltage variable resistor, coupled to the CMOS amplifier;
- wherein a first number of stages have a first degree value phase shift;
- and
- wherein a second number of stages have a second degree value phase shift.
A phase shift network, comprising:
- a number of stages coupled in series between an input and an output of the network, the output coupled to the input via a feedback line, wherein each stage includes:
- an amplifier;
- and
- an NMOS transistor coupled to the amplifier, wherein the NMOS transistor provides a variable resistor value to the network;
- and
- wherein the amplifier provides a gain and allows a small phase shift in each stage to eventually provide a signal which is 180 degrees out of phase with the input signal.
53 The phase shift network of claim 50, wherein an overall gain for each stage, including the amplifier and the NMOS transistor, is approximately 0.9 gm(RL) such that where gm(RL) is slightly larger than one (1) an overall gain of each stage is greater than one (1) and a condition for oscillation is satisfied.
A method of forming a CMOS phase shift oscillator, comprising:
- forming a number of stages coupled in series between an input and an output of the oscillator, wherein the output is coupled to the input via a feedback line, and wherein forming each stage includes:
- forming a CMOS amplifier;
- and
- forming a phase shift network coupled to the CMOS amplifier;
- and
- wherein forming the CMOS amplifier includes forming a CMOS amplifier which provides a gain and allows a small phase shift in each stage to provide an output signal at the output which is 180 degrees out of phase with an input signal received at the input of the oscillator.
62 The method of claim 60, wherein forming the CMOS phase shift oscillator includes forming a CMOS phase shift oscillator which provides an output signal at the output without the use of any L-C circuits.
A method of forming a CMOS phase shift oscillator, comprising:
- forming at least five stages coupled in series between an input and an output of the oscillator, wherein the output is coupled to the input via a feedback line, and wherein forming each stage includes:
- forming a CMOS amplifier;
- and
- forming a phase shift network coupled to the CMOS amplifier;
- and
- wherein forming each stage includes forming each stage such that a phase shift in each stage contributes to a total phase shift, and wherein a small phase shift is realized in each stage at a high frequency such that the at least five stages result in a high oscillation frequency.
A method of forming a phase shift network, comprising:
- forming a number of stages coupled in series between an input and an output of the oscillator, wherein the output is coupled to the input via a feedback line, wherein forming each stage includes:
- forming an amplifier, wherein forming the amplifier includes:
- forming an NMOS transistor;
- and
- forming a diode connected PMOS transistor coupled at a drain region to the NMOS transistor and acting as a load resistor, wherein the diode connected PMOS transistor has a low impedance, RL;
- and
- forming a phase shift device coupled to the amplifier;
- and
- wherein forming the amplifier includes forming an amplifier which provides a gain and allows a small phase shift in each stage to eventually provide an output signal at the output which is 180 degrees out of phase with an input signal received at the input.
A method of operating a voltage controlled phase shift oscillator, wherein the oscillator includes a number of stages having an amplifier and a phase shift network coupled to the amplifier, wherein each amplifier includes an NMOS transistor and a diode connected PMOS transistor acting as a load resistor with a low impedance, comprising:
- controlling phase shift by an externally applied voltage;
- and
- wherein controlling phase shift by an externally applied voltage includes using an NMOS transistor in the phase shift network as a voltage variable resistor having a resistance which is larger than the load resistance of the diode connected PMOS transistor of the amplifier.
A method of operating a voltage controlled phase shift oscillator, wherein the oscillator includes a number of stages each having an amplifier and a phase shift device coupled to the amplifier, wherein each amplifier includes an NMOS transistor and a diode connected PMOS transistor acting as a load resistor with a low impedance, comprising:
- increasing an oscillation frequency (fo) of the circuit by increasing the number of stages;
- and
- wherein increasing the oscillation frequency (fo) of the circuit by increasing the number of stages includes using an amplifier having an input capacitance, Cin, which is much smaller than a capacitance, C, in the phase shift device.
A method of operating a phase shift circuit, wherein the phase shift circuit includes a number of stages, each stage having an amplifier and a phase shift network coupled to the amplifier, wherein each amplifier includes an NMOS transistor and a diode connected PMOS transistor acting as a load resistor with a low impedance, comprising:
- controlling an oscillation frequency (fo) of the circuit by controlling a variable resistor value of an NMOS transistor in the phase shift network of any given stage;
- and
- controlling a phase shift in any given stage by an externally applied voltage.
Dependencies are inferred from the claim text.