Band-gap Reference Circuit Dynamic Capacitor Switching
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Solution Overview
Problem
Existing band-gap reference circuits face challenges in achieving low temperature sensitivity, high power supply rejection (PSR), and low output noise while maintaining a fast start-up time, which are essential for high-precision applications and production test requirements.
Innovation Solution
A band-gap reference circuit design incorporating a low impedance block, three capacitors, and transmission gates controlled by digital blocks to disconnect and reconnect capacitors based on trim or mission modes, allowing for efficient trimming and operation with low output noise and high PSR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large capacitors are used to achieve low output noise and high PSR, then output noise is reduced and PSR is improved, but start-up time increases
Solution Approach 1:
The patent applies dynamic switching of capacitor connections based on operational mode. During trimming mode, the large capacitor is disconnected to achieve fast start-up. During normal operation, the large capacitor is connected to provide low output noise and high PSR. This dynamic reconfiguration resolves the contradiction between fast start-up and low noise/high PSR performance.
Solution Approach 2:
The patent segments the capacitor network into multiple capacitors (first capacitor, second capacitor, third capacitor) that can be independently connected or disconnected based on operational requirements. This segmentation allows the system to optimize for either fast start-up (by disconnecting large capacitors) or low noise/high PSR (by connecting large capacitors), resolving the technical contradiction.
2Reliability
If RC filters are used to reject high-frequency noises, then output noise is reduced and PSR is improved, but start-up time increases due to large RC time constant
Solution Approach 1:
The patent dynamically controls the connection of RC filter components through switching elements. During trimming mode, the RC filter is disconnected to allow fast start-up. During normal operation, the RC filter is connected to provide noise rejection and high PSR. This dynamic control resolves the contradiction between fast start-up and noise filtering performance.
3Reliability
If trimming is performed with large capacitors connected, then low output noise and high PSR are achieved, but trimming time increases which increases chip cost
Solution Approach 1:
The patent implements dynamic switching where the large capacitor is disconnected during trimming operations to enable fast trimming, and connected during normal operation to provide low output noise and high PSR. This resolves the contradiction between trimming speed and noise performance by using the appropriate capacitor configuration for each operational phase.
Data Source
AI summary
A band-gap reference circuit includes a band-gap voltage reference core to provide a reference voltage; a low impedance block; three capacitors; two transmission gates to connect and disconnect the capacitors; and two digital control blocks. The three capacitors includes an output capacitor connected at an output of the low impedance block to ground; a small capacitor connected to an output of the band-gap voltage reference core; and a large capacitor connected to the two transmission gates. The band-gap voltage reference core includes an operational amplifier, wherein an output of the operational amplifier connects to an input of the low impedance block and the small capacitor, wherein the small capacitor is also connected to ground; and a combination of bipolar junction transistors, MOS-FET, resistors, capacitors, or FinFET devices that provides a reference voltage.