Class-AB Voltage-to-Current Converter With Switched Feedback
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Solution Overview
Problem
Existing voltage-to-current converters, particularly in RF transceiver designs, face inefficiencies in power consumption and performance due to their operation in class A or class AB modes, which lead to high power dissipation and limited degeneration resistor values, especially in semiconductor devices.
Innovation Solution
The development of a linear class-AB voltage-to-current converter circuit that includes a core amplifier circuit, feedback circuits, and a common mode feedback network, utilizing p-channel and n-channel Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) and constant current sources to optimize current output based on input voltage, reducing power consumption and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage-to-current converters operate in class A mode with transistors biased to conduct current at all times, then linearity is improved, but power consumption increases significantly
Solution Approach 1:
The patent implements class-AB operation where transistor biasing dynamically adapts to the input signal level. Transistors are biased to conduct during portions of the input cycle rather than continuously, allowing the circuit to transition between class-A and class-B operation based on signal amplitude, thereby reducing quiescent power consumption while maintaining linearity during normal operation
Solution Approach 2:
The patent changes the operating parameters of the transistors by adjusting bias currents and voltages to achieve class-AB operation. This involves modifying the DC operating point parameters to allow transistors to enter cutoff during portions of the cycle, fundamentally changing the operational regime from continuous conduction to intermittent conduction to reduce power consumption
2Use of energy by moving object
If voltage-to-current converters operate in class AB mode to reduce power consumption, then power efficiency is improved, but the degeneration resistor must be driven by the previous stage which increases power dissipation
Solution Approach 1:
The patent introduces an intermediate buffer stage or driver circuit between the previous stage and the degeneration resistor. This intermediary stage provides the necessary current drive capability to the degeneration resistor without requiring the previous stage to directly source the high currents needed, thereby isolating the power dissipation from the previous stage and improving overall power efficiency
Solution Approach 2:
The patent segments the current path by separating the high-current degeneration resistor drive function from the voltage signal path. This is achieved by using dedicated current source circuits or buffer stages that handle the high current requirements independently, allowing the voltage-to-current conversion function and the current drive function to be separated into distinct circuit blocks
3Device complexity
If practical degeneration resistors with limited values (tens or hundreds of ohms) are used in class AB converters, then device complexity is reduced, but the load on the driving stage increases resulting in higher power dissipation
Solution Approach 1:
The patent introduces intermediate buffer stages or driver circuits between the previous stage and the degeneration resistor. This intermediary stage provides the necessary current drive capability to the degeneration resistor without requiring the previous stage to directly source the high currents needed, thereby isolating the power dissipation from the previous stage and improving overall power efficiency
Solution Approach 2:
The patent applies local quality by providing enhanced current drive capability specifically at the degeneration resistor location through dedicated buffer stages or current source circuits. This localized enhancement of current sourcing capability allows the use of practical resistor values without imposing excessive load requirements on the overall system
Data Source
AI summary
A voltage-to-current converter circuit comprises an amplifier, a resistor, first and second feedback circuits, and an output circuit. The amplifier is configured to receive a differential input voltage signal. The resistor is coupled between first and second nodes of the amplifier. The first feedback circuit is coupled to a third node of the amplifier, provides feedback to the first and second nodes when the value of the input voltage signal is in a first range, and is turned off otherwise. The second feedback circuit is coupled to a fourth node of the amplifier, provides feedback to the first and second nodes when the value of the input voltage signal is in a second range different from the first range, and is turned off otherwise. The output circuit produces a differential current output signal having a value according to the value of the input voltage signal.