Controlled-Endpoint Sawtooth Oscillator Using Capacitor Charge Sharing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing sawtooth oscillator circuits face challenges in controlling the endpoints of a sawtooth waveform when they are suspended between the power supply and ground, due to finite control propagation delays and undershoot errors, leading to significant frequency errors and glitching on the power supply rail.
Innovation Solution
A controlled endpoint sawtooth signal generator circuit using a novel switched capacitor pair charge sharing architecture, where one endpoint is defined by a reference voltage and the other by capacitor ratio, allowing for precise control of both endpoints using a comparator and controlled switches, and synchronized by internal or external triggers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If low-impedance clamps are used to eliminate undershoot error at the end of capacitor discharge period, then endpoint control accuracy is improved, but discharge time increases due to required increased impedance in capacitor discharge path
Solution Approach 1:
The patent segments the discharge path into two distinct impedance zones: a high-impedance path through the clamp circuit for precise endpoint control, and a low-impedance path through the switch for rapid charge transfer. This segmentation allows each path to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent introduces a clamp circuit as an intermediary element that mediates between the timing capacitor and the reference voltage during discharge. This intermediary provides precise endpoint control by clamping the capacitor voltage to the reference level while isolating the main discharge path from the need for high impedance.
2Measurement precision
If low-impedance clamps are used to control endpoint accuracy, then frequency precision is improved, but substantial glitching occurs on the power supply rail due to transient loading by shunted discharge current
Solution Approach 1:
The patent extracts the harmful transient loading effect from the power supply rail by routing the discharge current through a dedicated clamp circuit path rather than through the main power supply connection. This extraction isolates the precision control function from the power supply disturbances.
Solution Approach 2:
The clamp circuit serves as an intermediary that absorbs and manages the discharge current, preventing it from directly loading the power supply rail. This intermediary element protects the power supply from transient effects while maintaining precise frequency control.
3Device complexity
If finite control propagation delays are present in comparative hysteretic techniques, then circuit simplicity is maintained, but significant errors occur in oscillator frequency due to undershoot
Solution Approach 1:
The patent applies preliminary action by pre-charging the timing capacitor to a voltage slightly above the reference level before discharge begins. This preliminary positioning compensates for the upcoming undershoot caused by propagation delays, ensuring the endpoint accuracy is maintained despite the delays.
Solution Approach 2:
The patent implements preliminary anti-action by designing the charge phase to overshoot the target voltage intentionally, creating a counterbalancing effect that anticipates and cancels out the undershoot that will occur during discharge due to finite propagation delays.
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
The solution enables precise control of both endpoints of the sawtooth waveform, reducing frequency errors and minimizing discharge current effects on the supply rail, resulting in accurate and stable oscillations with high discharge currents isolated from the supply rail.
Implementation Method 1
A first charge storage device has an output node to which a charging source is coupled
Implementation Method 2
in a second circuit state in which the first and second charge storage devices are interconnected for charge sharing
Data Source
AI summary
A controlled endpoint sawtooth waveform generator and methodology is implemented by a circuit that uses charge sharing between capacitors to produce a sawtooth having one or both endpoints that are suspended between the power supply rail and ground. The circuit may comprise a timing capacitor to which a charging source is coupled, and a switched capacitor coupled to the timing capacitor through a first controlled switch and to a source of switched capacitor reference voltage through a second controlled switch. The first and second controlled switches are responsive to a control signal, that may be internally or externally provided, for mutually exclusive switch operation. An output sawtooth thereby is produced having one endpoint determined by a fixed voltage source and the other endpoint in accord with the capacitance ratio of the timing and switched capacitors.