Digitally Controlled Oscillator Feedback Circuit for High PSRR
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Solution Overview
Problem
Existing digitally-controlled oscillators (DCOs) face challenges with power supply rejection ratio (PSRR), noise sensitivity, and limited frequency range, often requiring trade-offs between these characteristics, which affects their performance in integrated circuits.
Innovation Solution
A DCO design incorporating a current mirror, variable resistor, and negative feedback circuit, where the current mirror generates a supply current based on a reference current, and the variable resistor provides adjustable resistance via a digital control signal, while the negative feedback circuit stabilizes the reference current based on input node voltage, improving PSRR and reducing noise sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional DCO design is used, then the circuit structure is simple, but the power supply rejection ratio (PSRR) is poor and noise sensitivity is high
Solution Approach 1:
The patent introduces a negative feedback circuit that senses the voltage at the input node and adjusts the reference current accordingly. The feedback circuit includes a transistor whose gate is connected to the input node, creating a feedback loop that stabilizes the operating point and improves PSRR by counteracting power supply variations and noise disturbances.
Solution Approach 2:
The patent introduces an intermediate n-channel transistor between the current mirror and the variable resistor. This intermediary transistor acts as a buffer that isolates the reference current path from the oscillation circuit, reducing noise coupling and improving PSRR without significantly increasing overall circuit complexity.
2Adaptability or versatility
If the frequency range is extended, then the versatility improves, but the noise sensitivity increases
Solution Approach 1:
The negative feedback circuit maintains a stable operating point across the frequency range by continuously adjusting the reference current based on input node voltage. This feedback mechanism compensates for noise effects that would otherwise increase with wider frequency tuning, allowing extended frequency range without proportional noise sensitivity increase.
Solution Approach 2:
The patent uses a variable resistor controlled by digital control signals to adjust the oscillation frequency over a wide range. Combined with the feedback-stabilized reference current, this allows frequency parameter changes while maintaining low noise sensitivity through the stabilizing effect of the feedback circuit.
3Stability of the object's composition
If the reference current is increased to improve oscillation stability, then the stability improves, but the power consumption increases
Solution Approach 1:
The feedback circuit dynamically adjusts the reference current to maintain optimal oscillation stability. Instead of using a fixed high current, the feedback mechanism ensures the reference current is precisely what is needed for stable operation, avoiding excessive power consumption while maintaining stability through active control rather than brute-force current levels.
Solution Approach 2:
The negative feedback circuit automatically regulates the reference current based on the actual operating conditions at the input node. The circuit self-adjusts to maintain stability without external intervention, optimizing the balance between stability and power consumption by using only the necessary current level for each operating point.
Data Source
AI summary
A digitally-controlled oscillator (DCO) includes a current mirror configured to generate a reference current at a first output terminal thereof, and a supply current having a magnitude proportional to a magnitude of the reference current at a second output terminal thereof. An oscillation circuit is provided, which is responsive to the supply current at an input node thereof. This oscillation circuit generates a periodic output signal having a frequency that varies in response to changes in the magnitude of the supply current. A variable resistance circuit is provided, which is responsive to a first control signal having a magnitude that influences a value of a resistance provided between a first node thereof, which receives the reference current, and a second node thereof. A negative feedback circuit is provided, which has first and second current carrying terminals electrically coupled to the first output terminal of the current mirror and the first node of the variable resistance circuit, respectively, and a control terminal electrically coupled to the input node of the oscillation circuit.