Current Sampling Hold Circuit With Mirroring for Fast Low-Noise Setup
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Solution Overview
Problem
Current signal acquisition systems face inefficiencies due to limited setup time in canceling circuits, which affects the overall system efficiency and introduces noise when increasing bias current to improve setup speed.
Innovation Solution
A current sampling and holding circuit incorporating a canceling circuit and a mirroring circuit, where the mirroring circuit transfers current differences to maintain high currents and improve setup speed without increasing direct current, thereby reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the transconductance gm1 of the first P-type MOS transistor M1 is increased by adding a bias current source I1, then the setup speed of the canceling circuit 12 is improved, but current noise is introduced which affects the signal-to-noise ratio
Solution Approach 1:
The patent divides the current sampling and holding function into two separate circuits: a canceling circuit (for DC component cancellation) and a mirroring circuit (for AC signal sampling). This segmentation allows each circuit to be optimized independently - the canceling circuit can use higher bias current for fast setup without affecting the noise performance of the mirroring circuit that handles the actual signal.
Solution Approach 2:
The patent introduces a mirroring circuit as an intermediary between the sensor and the output. This mirroring circuit captures the AC signal component during the sampling phase and holds it during the hold phase, effectively mediating between the DC cancellation function and the AC signal output, thereby separating the noise-generating DC bias functions from the signal-processing functions.
2Quantity of substance
If the capacitance of the capacitor C0 of the current-type sensor is great, then the sensor can capture more signal energy, but the time constant τ1 becomes very great which lowers the setup speed of the canceling circuit 12
Solution Approach 1:
By separating the DC cancellation function (canceling circuit) from the AC signal sampling function (mirroring circuit), the patent allows the sensor capacitor C0 to maintain its large capacitance value for signal energy storage while the canceling circuit's setup speed is determined by its own bias current and equivalent capacitance, not by C0.
Solution Approach 2:
The canceling circuit performs preliminary DC component cancellation before the mirroring circuit samples the AC signal. This preliminary action removes the DC offset from the sensor output, allowing the subsequent AC-coupled mirroring circuit to operate with its full dynamic range without being affected by the large sensor capacitance C0.
3Productivity
If a large bias current is used to improve the setup speed of the canceling circuit 12, then the transconductance gm1 is increased and setup speed improves, but the signal-to-noise ratio of the signal acquisition system deteriorates
Solution Approach 1:
The patent segments the circuit functions so that the canceling circuit (handling DC) and mirroring circuit (handling AC signal) operate independently. This allows the canceling circuit to use high bias current for fast setup without degrading the signal-to-noise ratio, as the high-current path is electrically separated from the low-noise signal path in the mirroring circuit.
Solution Approach 2:
The mirroring circuit acts as a noise-isolating intermediary that captures the AC signal during sampling and holds it during the hold phase. This intermediary function protects the signal path from the noise generated by the high-bias-current canceling circuit, maintaining signal-to-noise ratio while allowing fast DC cancellation.
Data Source
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AI summary
A current sampling and holding circuit and a signal acquisition system are disclosed. The current sampling and holding circuit includes: a canceling circuit, connected in series between a VDD terminal and a current sensor, being conducted according to a first enable signal, and configured to output a current to cancel a direct-current component in the current sensor; and a mirroring circuit, connected in parallel between the VDD terminal and a ground voltage with the canceling circuit and the current sensor connected in series, and being conducted according to a second enable signal inverse to the first enable signal, and configured to perform current transfer according to a current difference between a mirror current of the shunt current and an output current of the current sensor. According to the present application, the setup speed of the current sampling and holding circuit is improved, and the noise output by the current sampling and holding circuit is reduced.