Combined Mixer-Filter Circuit Using an Active Inductor
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Solution Overview
Problem
Current filter circuitries in wireless communication systems face challenges in generating complex poles without significant current consumption, especially as signal bandwidths increase, leading to high power consumption and stability issues with op-amps and large silicon area requirements with passive inductors.
Innovation Solution
A combined mixer and filter circuitry using Hara's active inductor with a transistor, resistor, and capacitors, which generates complex poles with moderate quality factor, reusing direct currents and requiring minimal extra current consumption, and is scalable by adjusting capacitors and resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If op-amps are used to generate complex poles in filters, then the required attenuation at stop band is achieved, but current consumption increases significantly
Solution Approach 1:
The patent combines the mixer and filter functions into a single integrated circuit block. The filter is implemented using the existing mixer transistors (Q1-Q4) and their inherent capacitances, eliminating the need for separate op-amp based filter circuits. This merging achieves complex pole generation for stop band attenuation while reusing existing current paths, thereby avoiding the high current consumption associated with traditional op-amp implementations.
Solution Approach 2:
The mixer transistors themselves provide the filtering function through their inherent output capacitances (Cds) and the external capacitors (C1, C2) connected to their drains. The circuit uses its own internal components and current sources to generate the required complex poles, rather than requiring additional active components like op-amps that would consume extra current.
2Reliability
If passive inductors are used to generate complex poles, then the filter performance is improved, but silicon area increases significantly
Solution Approach 1:
The patent replaces physical passive inductors with an active inductor implementation using transistor Q5 and capacitor C3. This active inductor circuit replicates the inductive behavior needed for complex pole generation without requiring large spiral inductor structures, thereby achieving the same filter performance with minimal silicon area occupation.
Solution Approach 2:
The patent changes the implementation approach from passive physical inductors to an active circuit equivalent. By using transistor Q5 in a specific configuration with capacitor C3 and resistor R1, the circuit emulates inductive behavior through active components, allowing the same filtering function to be achieved with much smaller footprint suitable for integrated circuits.
3Reliability
If high order filters are implemented to achieve required stop band attenuation, then the attenuation performance is improved, but current consumption increases due to multiple op-amps
Solution Approach 1:
The patent achieves high order filtering (effectively 3rd order or higher) using a single integrated mixer-filter block that reuses the same transistors and current sources for multiple functions. The mixer transistors Q1-Q4 serve both mixing and filtering purposes, while transistor Q5 provides active inductance for complex pole generation. This multi-functional approach achieves high order attenuation performance without requiring multiple separate op-amp stages, thereby avoiding proportional increases in current consumption.
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 solution achieves high bandwidth with virtually no current consumption, is robust without feedback loops, and can fit various bandwidth requirements, eliminating stability issues and reducing power needs.
Implementation Method 1
a filter comprising an active inductor and a first capacitor... The active inductor comprises a transistor having a first terminal, a second terminal and a third terminal and a resistor connected between the first terminal of the transistor and a voltage potential
Implementation Method 2
The first capacitor is connected between the third terminal and a signal ground
Implementation Method 3
The active inductor comprises a transistor having a first terminal, a second terminal and a third terminal... The first terminal of the transistor (N1) is a gate or base terminal, the second terminal of the transistor (N1) is a drain or collector terminal, and the third terminal of the transistor (N1) is a source or emitter terminal
Implementation Method 4
a resistor connected between the first terminal of the transistor and a voltage potential
Data Source
Figure 1a~1b
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AI summary
A combined mixer and filter circuitry is disclosed. The combined mixer and filter circuitry comprises a mixer comprising a first input, a second input and an output. The combined mixer and filter circuitry further comprises a filter comprising an active inductor and a first capacitor. The active inductor comprises a transistor having a first terminal, a second terminal and a third terminal and a resistor connected between the first terminal of the transistor and a voltage potential. The first capacitor is connected between the third terminal and a signal ground and the second terminal of the transistor is connected to the second input of the mixer.