Linear Amplifier Level Shifting with Constant Current Control
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Solution Overview
Problem
Existing linear amplifiers face challenges in performing large amounts of level shift and precisely determining the level shift, especially when transitioning between different power supply voltage regions, leading to increased power consumption and variability in output common mode voltage.
Innovation Solution
Incorporating a constant current source that supplies a constant current to a node between series-connected input resistances, allowing for precise control of the level shift and enabling both level up and level down operations, with a method that includes a current generating resistance and a current mirror circuit to mirror the source current, thereby determining the amount of level shift independently of input resistance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional level shift circuit using input resistance and reference voltage is used, then the circuit structure is simple, but the amount of level shift is limited and cannot achieve large level shifts between different power supply voltage regions
Solution Approach 1:
The patent changes the fundamental parameter used for level shift from voltage-based (reference voltage) to current-based (constant current source). By introducing a constant current source that flows through the input resistance, the level shift amount becomes I_const × R_in, which can be independently controlled and achieves much larger shift amounts suitable for transitioning between different power supply voltage regions.
2Adaptability or versatility
If the input resistance or reference voltage is modified to change the level shift amount, then the level shift can be adjusted, but the voltage amplifier construction must be modified accordingly
Solution Approach 1:
The patent extracts the level shift function from the voltage amplifier construction by introducing a separate constant current source. This separates the level shift mechanism (I_const × R_in) from the amplifier core, allowing the voltage amplifier to maintain a fixed construction while the level shift amount is independently controlled by adjusting the constant current source.
3Adaptability or versatility
If multiple stages are used to achieve large level shift, then the required level shift amount can be achieved, but the power consumption and circuit area increase
Solution Approach 1:
The patent merges the level shift function with the single-stage voltage amplifier by introducing a constant current source at the input. This combination achieves large level shifts in a single stage, eliminating the need for multiple cascaded stages and thereby reducing overall power consumption and circuit area while maintaining the required level shift capability.
4Adaptability or versatility
If a constant current source is introduced to enable large level shift, then large level shift is achieved, but the circuit complexity increases
Solution Approach 1:
The constant current source serves multiple functions simultaneously: it generates the level shift voltage (I_const × R_in), provides bias current for the voltage amplifier, and enables independent control of the level shift amount. This multi-functionality justifies the added component while achieving significant performance improvement.
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 enables precise and large amount of level shift, reducing power consumption and circuit area by allowing variable gain and low-pass filter functions in a single stage, while maintaining signal amplitude and determining the common mode voltage accurately.
Implementation Method 1
The constant current generates a voltage drop equal to a difference between a first and a second common mode voltage across the first input resistance
Implementation Method 2
a current mirror circuit that mirrors the source current to generate the constant current
Data Source
AI summary
A linear amplifier that comprises a signal input terminal that receives an input signal having a first common mode voltage, a voltage amplifier having a non-inverting input terminal that receives a second common mode voltage, a first and a second input resistance connected in series from the signal input terminal to the inverting input terminal of the voltage amplifier, a feedback resistance connected between the inverting input terminal and the output terminal of the voltage amplifier, and a constant current source. The constant current source supplies a constant current to a middle node between the first and the second input resistances. The constant current generates a voltage drop, which is equal to a difference between the first and the second common mode voltages, across the first input resistance. Accordingly, the common mode voltage of the output signal is directly determined by the second common mode voltage.