Differential Switch Reverse Coupling for Off-State Isolation
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Solution Overview
Problem
Conventional differential switches experience significant signal leakage during the disabled-state, especially at high frequencies, which degrades off-state isolation.
Innovation Solution
The implementation of a differential switching device with a primary switch and a dummy switch, where the dummy switch is reverse-coupled to the primary switch in the disabled-state, effectively canceling off-state leakage currents by setting the dummy current source to zero or disabling it during the primary switch's on-state functioning, ensuring only leakage signals are canceled while intentional signals are not passed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional differential switch is used, then the device complexity is low, but the off-state isolation is poor due to signal leakage
Solution Approach 1:
A dummy switch is created as a copy of the primary switch, with identical transistor pair configuration and coupling structure. The dummy switch replicates the leakage characteristics of the primary switch, enabling cancellation through reverse coupling of their outputs while maintaining the same structural complexity as a conventional switch.
Solution Approach 2:
The primary switch and dummy switch are merged into a single integrated circuit structure with shared biasing networks and coupled outputs. Both switches operate simultaneously with their outputs combined through reverse coupling, achieving improved isolation while maintaining a compact unified design rather than separate independent switches.
2Reliability
If the dummy switch is always enabled, then off-state leakage cancellation is effective, but signal passing capability is lost during on-state
Solution Approach 1:
The dummy switch current source is made dynamically controllable, transitioning between enabled and disabled states based on the operational mode. During off-state, the dummy current source is enabled for leakage cancellation; during on-state, it is disabled to allow signal passing. This dynamic control adapts the circuit behavior to different operational requirements.
Solution Approach 2:
The dummy switch operates periodically in sync with the primary switch state transitions. When the primary switch is off, the dummy switch is enabled for cancellation; when the primary switch is on, the dummy switch is disabled. This periodic enable/disable action ensures the dummy switch assists only during the required off-state isolation period.
3Ease of operation
If the dummy current source is set to non-zero, then the dummy switch can pass intentional signals, but off-state leakage cancellation is compromised
Solution Approach 1:
The dummy current source is configured with a specific local property of being set to zero, distinguishing it from the primary current source which operates at non-zero levels. This localized zero-current condition in the dummy switch enables pure leakage cancellation without signal passing, while the primary switch maintains its full signal transmission capability through its non-zero current source.
Data Source
AI summary
Techniques are disclosed for reducing off-state leakage current in a differential switching device. The techniques can be embodied, for example, in a method that includes receiving a differential input signal at a differential input of each of a primary switch and a dummy switch. In an enabled-state of the device, the method further includes passing the differential input signal to a differential output of the primary switch. In a disabled-state of the device, the method further includes canceling off-state leakage current at the differential output of the primary switch, by virtue of the dummy switch having its differential output reverse-coupled to the differential output of the primary switch. The method may further include preventing the dummy switch from passing signals other than off-state leakage signals. The techniques can be embodied, for instance, in a switching device.