Feed-Forward Driver Circuit for Amplifier Distortion Correction
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Solution Overview
Problem
Conventional feed-forward error correction circuits in driver circuits for communication devices face challenges such as reduced gain and increased current demand, limiting their effectiveness in achieving high linearity and bandwidth due to amplifier distortion.
Innovation Solution
A feed-forward error correction topology using a voltage-controlled current source in the error-correcting amplifier, which reduces output current and maintains gain by minimizing current demand from the correction circuit, thereby maximizing linearity and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional feed-forward error correction circuits are used to compensate for amplifier distortion, then linearity is improved, but gain is reduced by up to about 50%
Solution Approach 1:
The patent introduces a buffer amplifier as an intermediary component between the error correction amplifier and the summing junction. This buffer amplifier acts as a mediator that isolates the error correction path from the main signal path, allowing the error correction amplifier to operate with high gain without loading down the main amplifier and reducing overall system gain.
Solution Approach 2:
The patent segments the error correction current path by introducing a separate buffer amplifier stage. This segmentation separates the current generation function (error correction amplifier) from the current delivery function (buffer amplifier), allowing each to be optimized independently - the error correction amplifier for high gain and the buffer for current delivery capability.
2Manufacturing precision
If conventional feed-forward error correction circuits source significant current to achieve high linearity, then linearity is improved, but current demand on main path and correction path increases
Solution Approach 1:
The buffer amplifier serves as an intermediary that handles the high current demand requirements, allowing the error correction amplifier to focus on generating accurate correction signals with minimal current. The buffer amplifier then delivers the necessary current to the summing junction without requiring the error correction amplifier to source significant current directly.
3Manufacturing precision
If negative feedback is used to compensate for amplifier distortion, then linearity is improved, but bandwidth and gain are limited
Solution Approach 1:
The patent inverts the conventional approach by using feed-forward error correction instead of negative feedback. Rather than using feedback to indirectly correct distortion (which limits bandwidth and gain), the system directly generates and injects correction signals in the forward path, enabling high linearity without compromising bandwidth or gain performance.
Data Source
AI summary
A driver circuit for a transmitter includes a main path in parallel with an error correction path used for feed-forward error correction. The main path has an amplifier for amplifying a data signal to be transmitted from the transceiver. In parallel with the amplifier is a feedforward error correction circuit that provides an error correction signal that compensates for distortion introduced by the amplifier when the error correction signal is combined with the amplifier's output. The error correction circuit is designed to have a high impedance output so that voltage swings in the data signal do not create a demand for significant current from the feedforward error correction circuit, thereby reducing the current of the error correction signal. As an example, it is possible for the current of the error correction signal to substantially match that which is required to cancel the amplifier distortion, thereby minimizing distortion of the signal.