Feedforward Amplifier Circuit With Lower Output Impedance
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Solution Overview
Problem
Existing amplifier circuits face issues with high output resistance and significant voltage drops across impedance elements, leading to increased distortion and instability due to the load imposed by feedforward networks, which compromise the driver stage's performance.
Innovation Solution
The amplifier circuit is reconfigured with a modified impedance network arrangement where the bridge element Z1 is connected to the feedback loop, reducing the linear current and output impedance, thereby minimizing the impact on the driver stage and maintaining distortion cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedforward network is used to cancel distortion in the output stage, then distortion cancellation is improved, but the driver stage is overloaded with significant linear current requirements and stability is compromised
Solution Approach 1:
The patent extracts the linear current path from the feedforward network by introducing a separate feedback path. The feedback network (Z5, Z6) carries the bulk of the linear output current, while the feedforward network (Z1, Z2, Z3, Z4) is relieved of this burden and only needs to handle distortion correction currents, thereby stabilizing the driver stage while maintaining distortion cancellation capability
Solution Approach 2:
The patent introduces a feedback network as an intermediary element that mediates the current distribution between the driver stage and load. This feedback network acts as a buffer that absorbs the linear current burden, allowing the feedforward network to focus solely on distortion correction without overloading the driver stage
2Measurement precision
If impedance element Z1 is used in the feedforward network, then distortion cancellation is achieved, but high frequency output resistance becomes relatively high due to the 0R1 to 0R3 resistance range
Solution Approach 1:
The patent merges the functions of Z1 with the feedback network by connecting Z1 in parallel with the feedback path. This combination allows the feedforward network to maintain its distortion cancellation function while the parallel feedback path provides a low-impedance route for high-frequency signals, effectively reducing the overall output resistance at high frequencies
Solution Approach 2:
The patent adds a feedback dimension to the circuit architecture, creating a two-path system (feedforward and feedback) that operates in parallel. This dimensional addition allows independent optimization of each path: the feedforward path for distortion cancellation and the feedback path for low output impedance, thereby resolving the high frequency output resistance issue
3Stability of the object's composition
If Z1 carries most of the output current, then the bridge balance can be maintained, but significant voltage drop occurs across Z1 which must be compensated by amplifier 10
Solution Approach 1:
The patent applies preliminary action by pre-balancing the bridge through the feedback network before the feedforward network operates. The feedback path (Z5, Z6) is configured to establish the primary current distribution and voltage balance, while the feedforward network (Z1, Z2, Z3, Z4) makes fine adjustments for distortion correction, thereby minimizing the voltage drop compensation burden on amplifier 10
Data Source
AI summary
An amplifier circuit that includes a first amplifier that has a first input that receives an input signal, a second input and an output. The amplifier circuit also includes a second amplifier that has a first input that is coupled to the output of said the amplifier and a second input. The circuit further includes a first impedance network Z1, a second impedance network Z2, a third impedance network Z3 and a fourth impedance network Z4. The first impedance network Z1 is coupled to a load and the second input of the second amplifier, the second impedance Z2 is connected the output of the first amplifier and the second input of the first amplifier, the third impedance Z3 is connected to the output of the first amplifier and the load, the fourth impedance Z4 is connected the output of the second amplifier and the second input of said first amplifier.