Chopper Amplifier Capacitor Sharing for Bandwidth and Area
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Solution Overview
Problem
Chopper stabilized amplifiers face a challenge in high-bandwidth applications due to the large chip area occupied by capacitors required for Miller compensation and notch filtering, limiting their usability in complex mixed signal systems.
Innovation Solution
The same integrated circuit capacitors are utilized to perform both Miller compensation and notch filtering functions, sharing 'symmetrical counterpart' or 'balance' capacitors to reduce the overall chip area required, with switching mechanisms synchronized with clock signals to maintain functionality without signal charge loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If higher transconductance Gm is used to increase bandwidth in a notch filtered chopper stabilized amplifier, then the bandwidth is improved, but the compensation capacitors and notch filter capacitors occupy an unacceptably large amount of integrated circuit chip area
Solution Approach 1:
The patent combines the Miller compensation capacitors (C2, C3) with the notch filter capacitors (C5, C6) into a single integrated circuit structure. The same physical capacitors perform both the Miller compensation function and the notch filtering function simultaneously, eliminating the need for separate capacitor sets and thereby reducing the total chip area occupied by capacitive elements.
Solution Approach 2:
The compensation capacitors C2 and C3 are designed to serve dual purposes: they provide Miller compensation for amplifier stability while simultaneously functioning as the notch filter capacitors C5 and C6 for ripple reduction. This multi-functionality allows a single capacitor structure to fulfill multiple critical roles, reducing overall component count and chip area.
2Speed
If larger compensation capacitors are used to achieve higher bandwidth, then the bandwidth is improved, but the physical size of the capacitors increases causing them to occupy more chip area
Solution Approach 1:
The patent merges the compensation capacitor function with the notch filter capacitor function into a single physical structure. By using the same capacitors C2 and C3 for both Miller compensation and notch filtering, the design avoids the need for larger separate capacitors, thereby maintaining compact physical dimensions while achieving the required bandwidth performance.
Solution Approach 2:
The capacitors C2 and C3 are designed as multi-functional elements that simultaneously provide frequency compensation and notch filtering. This universal design allows the capacitors to achieve higher bandwidth without requiring increased physical size, as they are not dedicated solely to compensation but share their function with notch filtering.
Data Source
AI summary
A chopper-stabilized amplifier (1B) having a first output (25) includes an input chopper (9) for chopping an input signal and applying it to the input of a first amplifier (2) and an output chopper (10) for chopping an output signal of the first amplifier and applying it to the input of a switched capacitor notch filter (30-1). Notch filtering of the chopped output signal is performed by coupling a first compensation capacitor (C2) between a first output (25) of the chopper-stabilized amplifier and an output (14A) of the output chopper by means of a first switch (55) in response to a filter clock (FILTERCLK) and coupling a second compensation capacitor (C3) between the first output and an input (22A) of a second amplifier (3) by means of a second switch (58) in response to the filter clock, and coupling the first compensation capacitor between the first output and the input of the second amplifier by means of a third switch (56) in response to the complement of the filter clock and coupling the second compensation capacitor between the first output and the output (14A) of the output chopper circuit (40) by means of a fourth switch (57) in response to the complement.