Bipolar Amplification Circuit With Dual Feedback Current Cancellation
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Solution Overview
Problem
Existing high impedance current source circuits, such as the Howland current pump, face challenges when multiple circuits are connected in parallel, particularly due to issues like harmonic distortion and nonlinearities introduced by bipolar transistors, which affect applications requiring high audio quality.
Innovation Solution
A bipolar amplification circuit using dependent current sources and sinks driven by an operational amplifier, with negative feedback signals of opposite polarities, and level shifting circuits to maintain appropriate voltage levels, along with a supply noise compensator to mitigate voltage disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Howland current pump circuit is used to create a high impedance current source, then the circuit can function as a current source, but harmonic distortion and nonlinearities occur when multiple circuits are connected in parallel
Solution Approach 1:
The circuit is segmented into separate current source and current sink portions, each handled by dedicated FETs (PMOS for source, NMOS for sink). This segmentation allows independent optimization of each current path and reduces interaction-induced nonlinearities when multiple circuits are paralleled.
Solution Approach 2:
The invention changes the operating parameters by using field effect transistors instead of bipolar transistors, and implements level shifting circuits to maintain FETs in their linear regions. This parameter change eliminates the inherent nonlinearities of bipolar transistors while preserving current source functionality.
2Ease of manufacture
If bipolar transistors are used in the current source circuit, then the circuit can be implemented, but nonlinearities are introduced that affect audio quality
Solution Approach 1:
The invention replaces expensive bipolar transistors with cheaper field effect transistors that can be easily manufactured. While FETs have different characteristics, they can be operated in their linear regions through proper biasing and level shifting, providing both ease of manufacture and low nonlinearities.
Solution Approach 2:
The invention changes the operating parameters by implementing level shifting circuits that maintain FETs in their linear regions of operation. This allows FETs to replace bipolar transistors while achieving lower nonlinearities and better audio quality.
3Power
If multiple current source circuits are connected in parallel to increase current capability, then the current output is increased, but feedback current cancellation becomes difficult and performance degrades
Solution Approach 1:
The invention merges the current source and current sink functions into a unified circuit architecture where both are driven by the same operational amplifier. This merging allows automatic feedback current cancellation since the same feedback signal controls both the source and sink, enabling easy parallel connection for increased current capability.
4Stability of the object's composition
If dependent current sources and sinks are used with negative feedback, then amplification stability is improved, but circuit complexity increases
Solution Approach 1:
The operational amplifier serves multiple functions: it drives both the dependent current source and dependent current sink, and it processes both feedback signals simultaneously. This multi-functionality achieves stable amplification without proportionally increasing circuit complexity, as the same core component handles multiple tasks.
Data Source
AI summary
A bipolar amplification circuit has a control amplifier (101), a dependent current source (102) configured to supply current to an output terminal (104) and driven by an output from the control amplifier (101). A dependent current sink (103) is configured to receive current from the output terminal (104) and is also driven by the output from the control amplifier (101). The control amplifier includes an inverting input (105) and an input signal is supplied to this inverting input. A negative feedback signal of a first polarity is supplied to the inverting input from said dependent current source and a negative feedback signal of a second polarity is supplied to said inverting input from said dependent current sink.