Charge Pump Circuit with Dummy Switches for Noise Cancellation
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Solution Overview
Problem
Prior charge pump circuits suffer from current mismatch and noise-induced issues due to switching activities, leading to performance degradation and clock jitters in phase lock loops, with existing solutions being complex and ineffective in addressing these problems.
Innovation Solution
A charge pump circuit design incorporating an integrating capacitor and a switching device controlled by multiple logical signals, which operates in integrating and charge sharing phases to manage charge injection and sharing, and uses a modulating signal to suppress noise-induced spectral components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional charge pump circuits are used with current sources and switches, then the basic charge pumping function is achieved, but current mismatch and noise-induced spectral components occur due to manufacturing variations and switching activities
Solution Approach 1:
The patent creates a dummy switch that copies the timing and control signals of the real switches (120 and 140) to generate compensating currents. This dummy switch replicates the switching behavior without actually connecting to the charge pump output, thereby generating noise currents that mirror and cancel the harmful switching noises from the real switches.
Solution Approach 2:
The patent introduces a dummy current source (210) as an intermediary element that generates compensating currents to cancel the harmful effects of switching activities. This intermediary current source acts as a mediator between the switching noise and the charge pump output, injecting canceling currents through switches (220, 240) to neutralize the noise without requiring direct modification of the original current sources or switches.
2Measurement precision
If operational amplifiers and complex cancellation circuits are used to address current mismatch, then some accuracy improvement is achieved, but circuit complexity increases significantly
Solution Approach 1:
Instead of using complex operational amplifier circuits to detect and correct current mismatch, the patent employs a simpler copying approach where dummy switches replicate the timing behavior of real switches. This copying mechanism achieves current mismatch compensation through timing alignment rather than complex active cancellation circuits, significantly reducing device complexity while maintaining precision.
Solution Approach 2:
The patent changes the control parameter from using operational amplifiers to directly controlling switch timing through logic signals (UP, DN, and their complements). By adjusting the timing parameters of the dummy switches to match the real switches, the system achieves current matching accuracy through parameter optimization rather than complex circuitry.
3Productivity
If switching activities are increased to improve charge transfer speed, then charge pump efficiency improves, but noise-induced voltage ripple and spectral components increase
Solution Approach 1:
The patent converts the harmful switching noise into a beneficial canceling signal by using the same switching activities to drive dummy switches that generate opposing currents. The noise generated by switching is transformed into a useful compensating mechanism, where the harmful voltage ripple is counteracted by equal and opposite currents from the dummy switch network, thereby maintaining high charge transfer speed while eliminating noise.
Solution Approach 2:
The patent employs periodic switching actions synchronized with the phase detector signals (UP and DN pulses). The dummy switches operate in periodic cycles that mirror the real switches, creating regular compensating current pulses that cancel the periodic noise from switching. This periodic action maintains efficient charge transfer while systematically eliminating noise at each switching cycle.
Data Source
AI summary
A charge pump circuit capable of canceling current mismatch and suppressing clock feedthrough. The charge pump circuit comprises a current source enabled by a first logical signal, a current sink enabled by a second logical signal, an integrating capacitor coupled to both the current source and the current sink, and a switching device coupled between the integrating circuit and an output node. The switching device has two states. The switching device is set to a first state whenever a third logical signal is asserted and one of the first logical signal, the second logical signal, and a modulating signal is enabled. The switching device is set to a second state whenever the third logical signal is de-asserted, or none of the first logical signal, the second logical signal, and the modulating signal are asserted.