Single-Stage Ring Oscillator with Programmable Resistance for Frequency Control
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Solution Overview
Problem
Conventional single-stage voltage controlled oscillators (VCOs) face issues with oscillation failure at low or high control signal values, leading to potential problems in closed loop PLL applications due to insufficient resistance for oscillation sustainment.
Innovation Solution
A single stage ring-oscillator design with both coarse and fine frequency control, utilizing n-channel latches and programmable resistor circuits to adjust resistance, ensuring oscillation across a range of control signal values, and minimizing p-channel transistor count to reduce Negative Bias Temperature Instability effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the control voltage Vcont is made very low, then the frequency of oscillation decreases, but transistors M9 and M10 become open circuits and oscillation fails
Solution Approach 1:
A current source is introduced as an intermediary element to replace the direct voltage control of transistors M9 and M10. This current source provides a stable bias current that ensures transistors M9 and M10 remain in the active region across the full frequency range, preventing them from becoming open circuits even at low oscillation frequencies.
Solution Approach 2:
The control mechanism is changed from voltage control to current control. By controlling the frequency through a current source rather than a voltage signal, the operating point of transistors M9 and M10 is maintained in the active region, ensuring reliable oscillation sustainment across the entire frequency range without the transistors becoming open circuits.
2Speed
If the control voltage Vcont is made very high, then the frequency of oscillation increases, but the effective resistance of transistors M9 and M10 becomes less than the minimum required to sustain oscillation
Solution Approach 1:
A current source is introduced as an intermediary element to replace the direct voltage control of transistors M9 and M10. This current source provides a stable bias current that ensures transistors M9 and M10 remain in the active region across the full frequency range, preventing them from becoming open circuits even at low oscillation frequencies.
Solution Approach 2:
The control mechanism is changed from voltage control to current control. By controlling the frequency through a current source rather than a voltage signal, the operating point of transistors M9 and M10 is maintained in the active region, ensuring reliable oscillation sustainment across the entire frequency range without the transistors becoming open circuits.
3Productivity
If the number of stages in the ring oscillator is decreased by a factor of 2, then the oscillation frequency doubles and power consumption is halved, but the oscillator may fail to oscillate under certain control signal conditions
Solution Approach 1:
A current source is introduced as an intermediary element to replace the direct voltage control of transistors M9 and M10. This current source provides a stable bias current that ensures transistors M9 and M10 remain in the active region across the full frequency range, preventing them from becoming open circuits even at low oscillation frequencies.
Solution Approach 2:
The control mechanism is changed from voltage control to current control. By controlling the frequency through a current source rather than a voltage signal, the operating point of transistors M9 and M10 is maintained in the active region, ensuring reliable oscillation sustainment across the entire frequency range without the transistors becoming open circuits.
Data Source
AI summary
A voltage controlled oscillator (VCO) having a single stage ring-oscillator having both coarse and fine control of the frequency of oscillation is described. In an embodiment the VCO may include a first n-channel latch having a first output and a second output; a first P-channel transistor coupled between a voltage supply and a first VCO output, where a gate of the first P-channel transistor is coupled to the first output of the first n-channel latch; a first programmable resistor circuit coupled between the first VCO output and the first output of the first n-channel latch; and a second n-channel latch coupled to the first VCO output.