Sampled Band-Gap Reference Circuit for Flicker Noise Reduction
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Solution Overview
Problem
Existing band-gap reference voltage generators are sensitive to transistor mismatches and flicker noise, which can cause instability and degrade performance in integrated circuits, especially in low noise and RF applications.
Innovation Solution
A sampled band-gap reference voltage generator circuit is implemented using a core circuitry with bipolar transistors, capacitors, and operational amplifiers, employing dynamic element matching and time-interleaved sampling to reduce offset and flicker noise, with the output voltage derived from the base-to-emitter voltages of bipolar transistors and adjusted using capacitors and switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional band-gap reference voltage generator circuits are used, then temperature stability is achieved, but transistor mismatch sensitivity and flicker noise increase
Solution Approach 1:
The patent employs chopper stabilization technique that periodically switches the circuit operation between two phases: a sampling phase where the reference voltage is generated, and a hold phase where the sampled value is maintained. This periodic action allows the circuit to refresh the reference voltage sample at regular intervals, preventing accumulation of offset errors and reducing sensitivity to transistor mismatches that would otherwise drift over time.
Solution Approach 2:
The patent uses capacitor-based sampling to create a temporary copy of the band-gap reference voltage during the sampling phase. This copied voltage is stored on capacitors and then used during the hold phase, allowing the circuit to reference a stable captured value rather than continuously relying on potentially mismatched transistor parameters. Multiple capacitors store copies of the reference voltage for different portions of the circuit.
2Temperature
If traditional band-gap reference voltage generator circuits are used, then temperature stability is achieved, but flicker noise increases
Solution Approach 1:
The chopper stabilization technique modulates the circuit operation periodically, switching between sampling and hold phases. This periodic action effectively moves the low-frequency flicker noise to higher frequencies during the sampling phase, where it can be filtered out, and maintains a clean reference voltage during the hold phase when the circuit operates from the stored capacitor values rather than active transistor pairs.
Solution Approach 2:
The patent introduces capacitors as intermediary energy storage elements between the active band-gap reference generation and the output. These capacitors act as buffers that decouple the noisy active switching operation from the clean reference voltage output, allowing the reference to be sampled and stored in a low-noise manner during the hold phase.
3Object-generated harmful factors
If chopper stabilization technique is applied, then flicker noise is reduced, but circuit complexity increases
Solution Approach 1:
The patent integrates the chopper stabilization functionality directly into the band-gap reference voltage generator core, rather than adding it as a separate external circuit. The same transistors and capacitors that generate the reference voltage also perform the sampling and holding functions, making the circuit elements serve multiple purposes: generating reference voltage, storing sampled values, and enabling chopper stabilization, thereby reducing overall complexity.
Solution Approach 2:
The patent combines the band-gap reference generation circuit with the chopper stabilization circuit into a unified structure. The sampling switches and capacitors are integrated with the differential pair and current mirror that generate the reference voltage, merging the voltage generation and noise reduction functions into a single coordinated system rather than separate stages.
Data Source
AI summary
Systems and methods for sampled band-gap reference voltage generators are described. An embodiment includes a band-gap reference voltage generator circuit that includes: a first load transistor, a second load transistor where the gates of the first and second load transistors are connected, a first bipolar transistor, a second bipolar transistor, where the bases of the first and second bipolar transistors are connected, a first capacitor where a first terminal of the first capacitor is connected to the emitter of the first bipolar transistor through a first switch and a second terminal of the first capacitor is connected to the emitter of the second bipolar transistor through a second switch.