Current Mirror Offset Buffering for Linearity and Bandwidth
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Solution Overview
Problem
Current mirror circuits face challenges in achieving high linearity and wide signal bandwidth, as linearity is often traded off against bandwidth and power, especially at increasing fundamental input signal frequencies, leading to stability issues and degradation in dynamic range.
Innovation Solution
The implementation of current mirror arrangements with adjustable offset buffers, which include a buffer amplifier circuit and a buffer offset reduction circuit, allows for the adjustment of buffer offsets to minimize their impact on linearity and stability, enabling improved bandwidth and linearity by positioning the buffer outside the feedback loop and using a diamond stage or input/output side adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a buffer amplifier circuit is added to improve linearity and stability, then linearity and stability are improved, but device complexity increases
Solution Approach 1:
A buffer amplifier circuit is introduced as an intermediary component between the input and output of the current mirror. The buffer acts as a mediator that isolates the input and output, improving linearity and stability by preventing direct interaction between input signal variations and output current fluctuations, while managing the increased device complexity through careful buffer design and integration.
2Manufacturing precision
If buffer offset is reduced to improve linearity, then linearity is improved, but device complexity increases due to offset adjustment circuitry
Solution Approach 1:
Offset adjustment circuitry is incorporated to preliminarily compensate for buffer offset errors before they affect the main signal path. By providing adjustable offset cancellation mechanisms (such as trimmable resistors or programmable offset correction circuits), the system pre-corrects for buffer imperfections, improving linearity while managing complexity through integrated adjustment capabilities.
3Reliability
If buffer is positioned outside feedback loop to improve stability, then stability is improved, but measurement precision deteriorates due to buffer offset
Solution Approach 1:
The buffer amplifier is extracted from the feedback loop to eliminate the stability issues caused by feedback interactions. By positioning the buffer outside the feedback path, the system achieves improved stability as the buffer no longer introduces phase shifts or gain variations into the feedback signal, while separate offset correction mechanisms compensate for the buffer's inherent offset to maintain measurement precision.
4Speed
If current mirror is designed for wide bandwidth, then bandwidth is improved, but linearity deteriorates due to frequency-dependent effects
Solution Approach 1:
A buffer amplifier is introduced as an intermediary stage to decouple the frequency-dependent effects in the current mirror from the signal path. The buffer acts as a mediator that maintains signal integrity across wide bandwidth by isolating the input from output variations, while its high gain-bandwidth product ensures that linearity is preserved even at high frequencies where parasitic effects become significant.
Data Source
AI summary
An example current mirror arrangement includes a current mirror circuit, configured to receive an input current signal at an input transistor Q1 and output a mirrored signal at an output transistor Q2. The arrangement further includes a buffer amplifier circuit, having an input coupled to Q1 and an output coupled to Q2. The offset of the buffer amplifier circuit can be adjusted by including circuitry for an input or an output side offset adjustment or by implementing the buffer amplifier circuit as a diamond stage with individually controlled current sources for each of the transistors of the diamond stage. Providing an adjustable offset buffer in a current mirror arrangement may advantageously allow benefiting from the use of a buffer outside of a feedback loop of a current mirror, while being able to reduce the buffer offset due to mismatch between master and slave sides of the current mirror circuit.