Polyphase Filter Circuit Using MOSFET RC Matching Across Process Corners
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Solution Overview
Problem
Existing polyphase filter circuitry suffers from significant distortion, particularly at high frequencies, and is sensitive to process corners, leading to large amplitude and phase variations across different fabrication parameters.
Innovation Solution
The polyphase filter circuitry is designed with common-source amplifier and source-follower circuits using field-effect transistors and MOS capacitors, where the output resistance and capacitance define the frequency response, reducing the number of components and minimizing the impact of process variations by using the same device type for resistors and capacitors, thereby reducing phase/amplitude spread across process corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional polyphase filter circuitry is used, then the circuit can generate multiple output signals with different relative phases, but the circuit suffers from significant distortion particularly at high frequencies and large amplitude and phase variations across process corners
Solution Approach 1:
The patent applies homogeneity by implementing both resistors and capacitors using the same MOSFET device type. Specifically, resistors are implemented as MOSFETs operating in the linear region and capacitors as MOSFETs operating in saturation region. This homogeneous implementation ensures that all components experience identical process corner variations, thereby minimizing the spread of phase and amplitude across different fabrication corners and improving performance consistency.
Solution Approach 2:
The patent changes the operational parameters of MOSFETs to achieve different circuit functions. By adjusting the bias conditions and operating regions of MOSFETs, the circuit achieves the desired phase shifts and frequency responses while maintaining compatibility with standard CMOS fabrication processes. This parameter optimization reduces sensitivity to process variations.
2Speed
If polyphase filter circuitry operates at high frequencies, then the circuit can meet high-speed application requirements, but distortion is significantly exacerbated
Solution Approach 1:
The patent optimizes circuit parameters including MOSFET dimensions, bias currents, and capacitance values to achieve high-frequency operation with minimal distortion. By carefully selecting and tuning these parameters, the circuit maintains accurate phase relationships and signal integrity even at high operating frequencies, thereby meeting high-speed application requirements without significant distortion.
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 significantly reduces the effect of process corner variations, improving the performance and stability of polyphase filter circuitry by minimizing the spread of phase and amplitude across different fabrication corners, leading to more consistent and reliable operation.
Implementation Method 1
a capacitor C PFF connected to its source terminal; and for the common-source amplifier circuit, the output resistance R M1 seen at the source terminal of the field-effect transistor M1 and the capacitance of the capacitor C PFF are configured to define the frequency response
Data Source
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AI summary
Polyphase filter circuitry, comprising: an input node configured to receive an input signal VIN having a dominant frequency fPPF; and a common-source amplifier circuit, wherein: the common-source amplifier circuit comprises a field-effect transistor M1 with its gate terminal connected to the input node and with a capacitor CPFF connected to its source terminal; and for the common-source amplifier circuit, the output resistance RM1 seen at the source terminal of the field-effect transistor M1 and the capacitance of the capacitor CPFF are configured to define the frequency response of the common-source amplifier circuit so that, based on the input signal VIN, a signal VLEAD is generated at the drain terminal of the transistor M1 which leads the input signal VIN in phase by a given phase shift ΔφLEAD and a signal VLAG is generated at the source terminal of the transistor M1 which lags the input signal VIN in phase by a given phase shift ΔφLAG.