VCO Reference Current Feedback for Stable Clock Frequency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Voltage Controlled Oscillators (VCOs) are affected by process variations and bias voltage sources, leading to instability in the frequency of the output clock signal due to dependence on threshold voltage and bias voltage levels.
Innovation Solution
A VCO design that includes a reference current source module with an amplifier, resistor, and transistors, where the reference current is clamped to a reference voltage, independent of bias voltage and threshold voltage variations, using a main band-gap voltage reference circuit to generate a stable reference current, and an odd number of inverting modules to generate a clock signal with a frequency corresponding to the reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional reference current source module using MOS transistors is used, then the circuit can generate reference currents, but the reference current magnitude is affected by threshold voltage variations and bias voltage source variations, leading to frequency instability
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary component to actively control and stabilize the reference current. The amplifier compensates for threshold voltage variations by adjusting the gate voltage of the control transistor, thereby maintaining a stable reference current magnitude that is independent of MOS transistor threshold voltage variations and bias voltage source variations.
Solution Approach 2:
The patent implements a feedback mechanism where the operational amplifier continuously monitors the reference current and adjusts the control transistor's gate voltage to maintain constant current magnitude. This feedback loop eliminates the harmful effects of threshold voltage variations and bias voltage fluctuations on the reference current stability.
2Ease of manufacture
If MOS transistors are used for current generation, then the circuit can be implemented with standard components, but the current magnitude depends on threshold voltage which varies with process, affecting clock frequency accuracy
Solution Approach 1:
The operational amplifier provides continuous feedback control that compensates for process-induced threshold voltage variations. By monitoring the actual reference current and adjusting the control transistor gate voltage accordingly, the system maintains precise current magnitude control despite manufacturing variations in transistor threshold voltages.
Solution Approach 2:
The patent dynamically changes the gate voltage parameter of the control transistor through the operational amplifier to compensate for threshold voltage variations. This parameter adjustment allows the circuit to maintain stable reference current generation across different manufacturing processes and transistor variations.
Data Source
AI summary
A VCO includes a reference current module and a clock signal generating module. The reference current module generates a reference current according to a reference voltage. The clock signal generating module generates a clock signal according to the reference current. The reference current module utilizes the negative feed-back mechanism to keep the generated reference current at the predetermined size without being changed with the variation of the process and the bias source.