Resistive Mixer Negative Capacitance Circuit for Wideband Off-Impedance
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Solution Overview
Problem
Resistive mixers face a decrease in off-impedance due to parasitic capacitance between the drain and source of the mixer transistor, particularly noticeable in millimeter wave and terahertz wave bands, limiting frequency conversion efficiency.
Innovation Solution
A negative capacitance circuit is connected in parallel to the parasitic capacitance between the drain and source of the mixer transistor to cancel out the parasitic capacitance across a wide band, thereby increasing off-impedance and improving frequency conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inductor is attached between the drain and source to cancel parasitic capacitance, then off-impedance increases, but the effective frequency band becomes very narrow
Solution Approach 1:
The patent changes the electrical parameters of the cancellation circuit by using a series combination of capacitor and inductor instead of a single inductor. This parameter change allows the circuit to achieve parasitic capacitance cancellation across a wide frequency band while maintaining high off-impedance, resolving the contradiction between narrow bandwidth and effective compensation.
Solution Approach 2:
The patent employs a composite cancellation circuit structure combining capacitor and inductor elements working together. This composite approach creates a more versatile solution that can handle parasitic capacitance across broader frequency ranges compared to a single-component solution, thereby expanding the effective frequency band while maintaining reliability.
2Productivity
If the mixer transistor is used in millimeter wave and terahertz wave bands, then frequency conversion capability improves, but parasitic capacitance causes significant off-impedance decrease
Solution Approach 1:
The patent introduces a cancellation circuit as an intermediary element between the drain and source of the mixer transistor. This intermediary circuit actively compensates for the parasitic capacitance effect, allowing the mixer to operate effectively in millimeter wave and terahertz bands without suffering from significant off-impedance degradation.
3Productivity
If drain impedance is made smaller when transistor is ON, then conversion efficiency improves, but parasitic capacitance causes signal leakage to ground when transistor is OFF
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring the cancellation circuit to counteract the parasitic capacitance before it can cause signal leakage. The cancellation circuit is designed to provide opposite impedance characteristics that neutralize the parasitic effect, preventing signal from leaking to ground when the transistor is in the OFF state, thus maintaining both conversion efficiency and signal integrity.
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 negative capacitance circuit effectively cancels out parasitic capacitance across a wide band, enhancing off-impedance and frequency conversion efficiency by preventing signal flow to ground when the transistor is OFF, as demonstrated by simulation results showing increased impedance across higher frequencies.
Implementation Method 1
there is a parasitic capacitance Cp between a drain and a source of the mixer transistor 1
Implementation Method 2
a negative capacitance circuit (2) connected between the drain and a source of the mixer transistor (1)
Data Source
AI summary
A negative capacitance circuit is connected between a drain and a source of the mixer transistor. With this configuration, the negative capacitance circuit is connected in parallel to a parasitic capacitance generated between the drain and the source of the mixer transistor, and the parasitic capacitance can be canceled out in a wide band by the negative capacitance circuit connected in parallel.