Ring Oscillator VCO Layout for Lower Gain and Wideband Modulation
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Solution Overview
Problem
Conventional ring oscillator circuits exhibit high gain, making it difficult to achieve wide bandwidth frequency modulation and resulting in undesirable phase noise due to the need for small input signals and additional circuitry.
Innovation Solution
A ring oscillator circuit design where only one inverter stage responds to a variable input voltage, while the remaining stages operate at a constant, filtered voltage, reducing the overall gain by a factor of (2N+1 and enabling direct wideband frequency modulation without additional multiplier circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional ring oscillator circuit is used, then the circuit structure is simple and inexpensive, but the gain is too high causing difficulty in achieving wide bandwidth frequency modulation and resulting in undesirable phase noise
Solution Approach 1:
The patent divides the ring oscillator circuit into two distinct segments: a variable voltage inverter stage that responds to frequency modulation input signals, and constant voltage inverter stages that provide stable oscillation. This segmentation isolates the gain-producing element to only one stage, reducing overall circuit gain by a factor of (2N+1) while maintaining the simple ring oscillator structure.
2Ease of manufacture
If a conventional ring oscillator circuit is used, then the circuit structure is simple, but small input signals are needed which reduces signal-to-noise ratio and increases phase noise
Solution Approach 1:
The patent extracts the voltage control function from all inverter stages and concentrates it in only one variable voltage inverter stage. The other stages use constant voltages and are removed from the gain path. This extraction eliminates the amplification of noise that occurs when multiple stages respond to variable voltages, significantly reducing phase noise while keeping the circuit simple.
3Adaptability or versatility
If a low-frequency VCO circuit with multiplier circuits is used, then the desired frequency modulation index can be achieved, but the device complexity increases
Solution Approach 1:
The patent makes the ring oscillator circuit universally applicable to wide bandwidth frequency modulation by modifying its internal structure. The constant voltage inverter stages provide stable oscillation while the single variable voltage stage provides controlled frequency deviation. This multi-functional design allows the circuit to directly achieve frequency modulation without requiring external multiplier circuits, reducing overall system complexity.
Data Source
AI summary
A ring oscillator circuit having an odd plurality of inverter stages (i.e., 2N+1 stages). In accordance with one embodiment of the present invention, only one of the inverter stages is operated in response to a variable input voltage, while the remaining inverter stages are operated in response to a highly filtered constant input voltage. The inverter stages that operate in response to the constant input voltage oscillate at a base frequency. The inverter stage that operates in response to the variable input voltage causes the frequency of the output signal to deviate from the base frequency by an amount determined by the variable input voltage. In this manner, the variable voltage inverter stage implements frequency control for the ring oscillator. The gain of the ring oscillator circuit is reduced by a factor of (2N+1) with respect to the gain of a conventional ring oscillator.