Relaxation Oscillator Circuit With Dummy Switches for Stable Frequency
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Solution Overview
Problem
Relaxation oscillator circuits experience variations in clock frequency due to power supply voltage and temperature fluctuations, leading to response delays and power supply voltage dependence of oscillation frequency.
Innovation Solution
The oscillator circuit employs a configuration with dual constant current sources and RS flip-flop circuits, along with dummy switches that control capacitor charging and discharging, to reduce power supply voltage dependence by shortening the time required for the comparator output to reach a high level, thereby offsetting response delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current restriction is performed using a constant current source to reduce comparator threshold variation, then threshold stability is improved, but response time increases and power supply voltage dependence of oscillation frequency worsens
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to a voltage close to the comparator threshold before the actual comparison operation. This is achieved through a pre-charge transistor that activates before the main switching transistor, bringing the capacitor voltage near the threshold level in advance. As a result, when the main switching occurs, the capacitor reaches the threshold voltage much faster, significantly reducing the comparator response time while maintaining threshold stability through the constant current source.
2Reliability
If current restriction is performed using a constant current source, then threshold variation is reduced, but oscillation frequency becomes dependent on power supply voltage
Solution Approach 1:
By pre-charging the capacitor to near-threshold voltage before the main switching event, the patent reduces the time required for the capacitor to reach the threshold during normal operation. This preliminary action ensures that the oscillation period is dominated by the pre-charge phase rather than the comparison phase, making the overall oscillation frequency less sensitive to power supply voltage variations while maintaining threshold stability through the constant current source.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces power supply voltage dependence of oscillation frequency by minimizing response delays and ensuring consistent oscillation timing across varying voltage levels.
Implementation Method 1
a first voltage comparator that receives supply of a power supply voltage via a first constant current source, the first voltage comparator outputting a first signal of a logical level 0 when an electric potential input to an input terminal exceeds a threshold, the first voltage comparator outputting a first signal of a logical level 1 when an electric potential input to the input terminal is the threshold or less
Implementation Method 2
a second voltage comparator that receives supply of the power supply voltage via a second constant current source, the second voltage comparator outputting a second signal of a logical level 0 when an electric potential input to an input terminal exceeds the threshold, the second voltage comparator outputting a second signal of a logical level 1 when an electric potential input to the input terminal is the threshold or less
Implementation Method 3
a first charge/discharge unit that includes a first conductivity type first transistor and a second conductivity type second transistor, the first transistor and the second transistor having respective drains coupled to one another, the first transistor and the second transistor being coupled to another end of the first capacitor and an input end of the first voltage comparator via a first node and complementary turning on and off according to the first oscillation signal, the first charge/discharge unit charging and discharging the first capacitor based on the first oscillation signal
Implementation Method 4
a second charge/discharge unit that includes a first conductivity type third transistor and a second conductivity type fourth transistor, the third transistor and the fourth transistor having respective drains coupled to one another, the third transistor and the fourth transistor being coupled to another end of the second capacitor and an input end of the second voltage comparator via a second node and complementary turning on and off according to the second oscillation signal, the second charge/discharge unit charging and discharging the second capacitor based on the second oscillation signal
Implementation Method 5
a first dummy switch coupled to the first node, controlled to be on and off according to a signal level of the second oscillation signal, and adding a predetermined capacity to the first node during an on state
Implementation Method 6
a second dummy switch coupled to the second node, controlled to be on and off according to a signal level of the first oscillation signal, and adding a predetermined capacity to the second node during an on state
Data Source
AI summary
An oscillator circuit includes a first comparator that outputs a first signal indicative of a comparison result between an input potential and a threshold, a second comparator that outputs a second signal indicative of a comparison result between an input potential and the threshold, a RS flip-flop circuit that receives the first signal and the second signal and outputs first and second oscillation signals, a first charge/discharge unit that charges and discharges a first capacitor based on the first oscillation signal, a second charge/discharge unit that charges and discharges a second capacitor based on the second oscillation signal, a first dummy switch controlled to be on and off according to the second oscillation signal and adding a predetermined capacity to a first node, and a second dummy switch controlled to be on and off according to the first oscillation signal and adding a predetermined capacity to a second node.