Multi-Tanh Transconductor Circuit With Adjustable Linearity
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Solution Overview
Problem
Existing transconductor circuits with the multi-tanh design face challenges in controlling and varying transconductance without degrading linearity due to fixed offset voltage ratios between differential amplifiers.
Innovation Solution
Incorporating resistance circuits with diodes and transistors in parallel, where one transistor forms a diode and the other provides negative transconductance, allowing for adjustment of effective transconductance through emitter area ratios without affecting linearity, and using a controllable current source to manage transconductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ratio of quiescent voltage drop across resistors and offset voltage is kept constant to maintain linearity, then linearity is preserved, but transconductance cannot be controlled or varied
Solution Approach 1:
The patent introduces controllable current sources that allow dynamic adjustment of transconductance values while preserving the constant ratio relationship between voltage drops and offset voltages. This enables the circuit to adapt transconductance for different operating conditions without sacrificing linearity, resolving the contradiction between fixed linearity requirements and variable transconductance needs
Solution Approach 2:
The patent changes the operational parameters by introducing multiple current sources with different controllable values. By varying these current parameters while maintaining their proportional relationships, the circuit achieves adjustable transconductance while preserving the linearity condition that requires constant voltage drop ratios
2Reliability
If emitter area ratios are used to generate different offset voltages in differential amplifiers, then linearity is improved, but transconductance becomes fixed and cannot be varied
Solution Approach 1:
The patent combines the fixed emitter area ratios (which provide excellent linearity) with dynamically controllable current sources. This hybrid approach maintains the beneficial fixed geometric relationships for linearity while adding dynamic control capability through electrical parameters, allowing transconductance adjustment without compromising the linearity established by the emitter area ratios
3Reliability
If multiple differential amplifiers with different offset voltages are used in parallel, then linearity is enhanced, but device complexity increases
Solution Approach 1:
The patent makes the current sources universal and controllable, allowing the same multi-differential-amplifier structure to serve multiple functions: maintaining linearity through fixed emitter area ratios and enabling transconductance adjustment through controllable current values. This multi-functionality reduces the need for separate circuits for different purposes, thereby managing complexity
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
Enables the adjustment of transconductance while maintaining the linearity of the transconductor circuit, allowing for flexible operation without degrading performance.
Implementation Method 1
Each of the first and second resistance circuits includes at least one diode coupled between the respective differential amplifier and the at least one current source in a forward direction
Implementation Method 2
each of the first and second resistance circuits includes a transistor having a controlled path coupled in parallel to the diode. The respective diode includes a first transconductance and the respective transistor is controlled at the control node to provide a second transconductance, wherein the second transconductance is negative with respect to the first transconductance
Implementation Method 3
the transistors T1 to T4 are bipolar transistors... the offset voltages are generated by emitter area ratios A
Data Source
AI summary
A transconductor circuit, particularly according to the multi-tanh principle, having a first input node and a second input node, a first differential amplifier coupled to the first and second input nodes, and having a first offset voltage, and a second differential amplifier coupled to the first and second input nodes, and having a second offset voltage different from the first offset voltage. A first resistance circuit is coupled between the first differential amplifier and at least one current source, and a second resistance circuit is coupled between the second differential amplifier and the at least one current source. Varying of the current sources enables control of the transconductance without degrading linearity.