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US 10,483,913 B2Granted
Low power crystal oscillator
AssigneeQUALCOMM Incorporated
InventorsAli Najafi, Soheil Golara, Rabih Makarem, Shervin Moloudi
Life of this patent
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Abstract
A Pierce oscillator is provided with a transconductance amplifier transistor having a DC drain voltage that is regulated to equal a reference voltage independently from a DC gate voltage for the transconductance amplifier transistor.
Claims13
A circuit, comprising:
- a first transistor;
- a current source for driving a drain of the first transistor with a bias current;
- a first decoupling capacitor for isolating a direct current (DC) drain voltage for the first transistor from a DC gate voltage for the first transistor, wherein a gate of the first transistor is configured to be biased by an AC input voltage from a crystal through the first decoupling capacitor;
- a first inverter configured to invert a voltage at a terminal of the first decoupling capacitor;
- a second inverter configured to invert an output signal from the first inverter to provide an output voltage for the circuit;
- an operational amplifier configured to further bias the gate of the first transistor responsive to a comparison between the DC drain voltage and a reference voltage to regulate the DC drain voltage to equal the reference voltage;
- and
- a reference inverter including a reference PMOS transistor having a source connected to a power supply node for supplying a power supply voltage, a reference NMOS transistor having a source connected to ground and having a drain connected to a drain of the reference PMOS transistor, and a reference resistor connected between the drain of the reference NMOS transistor and a reference node for supplying the reference voltage, wherein the reference node is connected to a gate of the reference PMOS transistor and to a gate of the reference NMOS transistor, and wherein the reference inverter is matched to the first inverter and to the second inverter.
5 more elements
The circuit of 7, further comprising a second decoupling capacitor coupled between the terminal of the first decoupling capacitor and a gate of the PMOS current source transistor.
A method of oscillating an output signal, comprising:
- biasing a direct current (DC) gate voltage of a gate of a first transistor in a Pierce oscillator by driving a drain of the first transistor with a current from a current source;
- isolating the gate from the drain through a first decoupling capacitor;
- generating a reference voltage using a reference inverter such that the reference voltage equals a threshold voltage of the reference inverter;
- amplifying a difference between the reference voltage and a DC drain voltage for the drain to bias an alternating current (AC) gate voltage for the gate to cause the DC drain voltage to equal the reference voltage;
- driving the gate of the first transistor with an oscillating voltage from a crystal through the first decoupling capacitor;
- inverting the oscillating voltage in a first inverter to form an inverter output signal;
- and
- inverting the inverter output signal in a second inverter to form an oscillating output signal, wherein the reference inverter is matched to the first inverter and to the second inverter.
5 more elements
Dependencies are inferred from the claim text.