Current Mirror Feedback Loops for Low Impedance and Wide Bandwidth
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Solution Overview
Problem
Current mirrors in electronic devices face challenges in achieving both high linearity and wide signal bandwidth, as linearity is typically traded off against bandwidth and power, limiting their dynamic range in applications such as communication and automotive systems.
Innovation Solution
The implementation of a current mirror circuit with a transistor matrix forming two feedback loops, a fast low-gain loop and a slow high-gain loop, reduces input impedance and suppresses nonlinear voltage swings, thereby enhancing linearity and signal bandwidth by dominating loop gain at different frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional current mirror circuit is used, then the circuit structure is simple, but the linearity and signal bandwidth are limited due to high input impedance and nonlinear voltage swings
Solution Approach 1:
The feedback path is segmented into multiple parallel loops with different gains and bandwidths. The first loop provides high gain for low frequencies while the second loop provides low gain for high frequencies, allowing each loop to be optimized independently for its target frequency range, thereby improving overall linearity without excessive complexity
Solution Approach 2:
The circuit dynamically switches between different feedback loops based on frequency. At low frequencies, the high-gain loop dominates to provide excellent linearity, while at high frequencies, the low-gain loop becomes dominant to maintain stability and extend bandwidth, creating a dynamic adaptation to operating conditions
2Manufacturing precision
If the input impedance of the current mirror is high, then the circuit is easier to drive, but the nonlinear voltage swing increases which degrades linearity and bandwidth
Solution Approach 1:
Negative feedback is applied through multiple parallel loops that sense the output current and adjust the input transistor's base voltage to compensate for nonlinearities. This feedback mechanism reduces the effective input impedance and suppresses voltage swings, thereby improving linearity while maintaining ease of operation through the collaborative action of multiple loops
3Manufacturing precision
If a single high-gain feedback loop is used, then linearity is improved at low frequencies, but the bandwidth is limited due to stability constraints
Solution Approach 1:
The frequency range is segmented into two bands, each handled by a dedicated feedback loop. The first loop with higher gain handles low frequencies where linearity is critical, while the second loop with lower gain handles high frequencies where bandwidth is critical, allowing the system to achieve both objectives simultaneously without the stability constraints that would limit a single high-gain loop
Solution Approach 2:
The feedback loop parameters (gain and bandwidth) are changed across different frequency ranges. By having two loops with different parameter sets operating in parallel, the system adapts its effective feedback characteristics to the operating frequency, achieving high linearity at low frequencies and extended bandwidth at high frequencies
Data Source
AI summary
An example current mirror arrangement includes a current mirror circuit having an input transistor and an output transistor, where the base/gate terminal of the input transistor is coupled to its collector/drain terminal via a transistor matrix that includes a plurality of transistors. Transistors of the transistor matrix, together with the input transistor, form two parallel feedback loops, such that the input transistor is part of both loops. The first loop is a fast, low-gain loop, while the second loop is a slow, high-gain loop. At lower input frequencies, the high-gain loop may properly bias and accurately generate voltage at the base/gate terminal of the input transistor, while at higher input frequencies the fast loop may significantly extend the linear operating frequency band. Consequently, a current mirror arrangement with improvements in terms of linearity and signal bandwidth may be realized.