Ring Oscillator Bias Circuit for Stable Frequency Across PVT
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Solution Overview
Problem
Non-crystal oscillators exhibit significant frequency variations due to temperature, process, and supply voltage changes, making them unstable, and existing compensation circuits are complex and area-intensive, requiring special devices like BJTs.
Innovation Solution
A bias circuit for ring oscillators using differential delay cells with voltage-controlled resistors and a common current source, along with a replica arm and resistor arm, adjusts bias voltages to maintain a constant ratio of voltage swing to bias current, stabilizing oscillation frequency independently of process, temperature, and supply voltage variations without special devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bandgap reference circuits and BJT based compensation circuits are used to compensate for oscillator frequency variations, then frequency stability is improved, but area consumption increases and device complexity increases
Solution Approach 1:
The patent changes the parameter of biasing method by using voltage-controlled resistors with effective resistance dependent on first bias voltage, and a common current source controlled by second bias voltage, to stabilize oscillation frequency without requiring large area bandgap reference circuits or BJT based compensation circuits
Solution Approach 2:
The patent extracts the frequency stabilization function from complex bandgap reference circuits and BJT based compensation circuits, achieving the same stabilization effect using only basic CMOS processes with voltage-controlled resistors and a common current source, eliminating the need for special devices
2Reliability
If bandgap reference circuits and BJT based compensation circuits are used to compensate for oscillator frequency variations, then frequency stability is improved, but device complexity increases
Solution Approach 1:
The patent changes the parameter of device type by using only basic CMOS transistors and voltage-controlled resistors instead of BJT based compensation circuits, achieving frequency stabilization through parameter control (bias voltages) rather than complex device structures
Solution Approach 2:
The patent extracts the essential stabilization function from complex BJT based circuits and implements it using simple CMOS voltage-controlled resistors and current sources, removing the complexity of special devices while maintaining the stabilization effect
3Reliability
If reference clock and compensation circuits are used to stabilize output frequency, then frequency stability is improved, but precision tuning requirements increase
Solution Approach 1:
The patent implements self-service by using a common current source that automatically adjusts bias current based on bias voltage, and voltage-controlled resistors that self-regulate their effective resistance, eliminating the need for external reference clocks and manual precision tuning
Solution Approach 2:
The patent uses parameter changes through bias voltages to control the effective resistance of voltage-controlled resistors and the current of the common current source, providing automatic frequency stabilization without requiring precision tuning of multiple parameters
4Reliability
If BJT based compensation circuits are used to compensate for oscillator frequency variations, then frequency stability is improved, but process compatibility decreases
Solution Approach 1:
The patent extracts the frequency stabilization function from BJT based compensation circuits and implements it using only basic CMOS processes with voltage-controlled resistors and MOS transistors, removing the requirement for special processing steps while maintaining stabilization capability
Solution Approach 2:
The patent achieves frequency stabilization through parameter control (bias voltages affecting effective resistance and current) using standard CMOS devices, making the circuit compatible with simple CMOS processes without requiring special BJT fabrication steps
Data Source
AI summary
Bias circuits to stabilize oscillation in ring oscillators, oscillators, and methods to stabilize oscillation in ring oscillators are provided. The ring oscillator includes a plurality of differential delay cells, each including a pair of input transistors, a pair of voltage-controlled resistors, and a common current source. The bias circuit includes a replica arm that includes a replica of one of the voltage-controlled resistors, and a resistor arm that includes a fixed resistor. The bias circuit supplies bias voltages to the differential delay cells such that ratio of voltage swing to bias current of the delay cell is kept constant by referring the ratio to the fixed resistor.