Switched Capacitor Driver Feedback Using Track-and-Hold Masking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing switched capacitor circuit drivers require amplifiers with low output impedance and wide bandwidth, leading to increased power consumption, complexity, and cost, which is not necessary if the voltage dip at the beginning of the charging phase can be masked.
Innovation Solution
Incorporating a track and hold circuit in the feedback network to mask the voltage dip at the beginning of the charging phase, allowing for a simpler, compact, and low-power amplifier and feedback network, eliminating the need for low output impedance and wide bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an amplifier with low output impedance is used to drive the switched capacitor circuit, then the charging transient is fast and the input voltage is copied accurately, but the power consumption and circuit complexity increase significantly
Solution Approach 1:
The patent introduces a track-and-hold circuit as an intermediary component between the amplifier and the switched capacitor circuit. This mediator captures the amplifier output voltage during the tracking phase and holds it during the charging phase, allowing the amplifier to operate with higher output impedance without degrading the voltage copying accuracy at the capacitor. The track-and-hold circuit absorbs the impedance mismatch issue, enabling simpler amplifier design.
2Speed
If the output impedance of the amplifier is reduced to counteract high switch resistance, then the charging transient becomes faster, but the power consumption increases
Solution Approach 1:
The patent segments the charging process into two distinct phases: a tracking phase where the amplifier actively charges the capacitor, and a hold phase where the track-and-hold circuit maintains the voltage. During the hold phase, the amplifier can reduce its drive strength or enter a lower-power state since the voltage is being maintained by the held charge rather than continuous amplification. This temporal segmentation allows faster charging when needed while reducing power consumption during the maintenance phase.
3Reliability
If a wide-bandwidth amplifier is used to handle the charging transient, then the voltage settles properly, but the power consumption increases
Solution Approach 1:
The track-and-hold circuit performs preliminary action by capturing and storing the amplifier output voltage during the tracking phase before the charging phase begins. This preliminary voltage capture allows the main amplification and settling process to occur during the tracking phase when the system is actively powered, while the hold phase can operate with reduced power consumption since the voltage is already established and being maintained by the held charge rather than requiring continuous high-bandwidth amplification.
4Measurement precision
If offset-compensation techniques such as chopping or auto-zeroing are used to reduce input-referred offset, then the offset is reduced, but the bandwidth of the amplifier is limited
Solution Approach 1:
The patent extracts the offset compensation function from the main amplifier path by using the track-and-hold circuit to capture a clean reference voltage during the tracking phase. The held voltage inherently contains the offset-free information, allowing the amplifier to operate without complex offset-compensation techniques during the charging phase. This extraction of the offset issue from the continuous amplification path enables the amplifier to maintain wide bandwidth while still achieving low effective offset through the hold circuit's reference capture.
Data Source
AI summary
There is described a driver for a switched capacitor circuit (230, 330), the driver comprising (a) a voltage amplifier (210, 310) comprising a signal input (212, 312), a feedback input (214, 314) and an amplifier output (216, 316), and (b) a feedback network (220) coupled between the amplifier output (216, 316) and the feedback input (214, 314). The feedback network comprises a track-and-hold circuit (222) adapted to mask a voltage dip occurring at the amplifier output (216, 316) at the beginning of a switched capacitor circuit charging phase. There is also described a switched capacitor circuit comprising such a driver, a sensor device, and a method of driving a switched capacitor circuit.