Bandgap Reference Circuit With Filtered Control Loop for Low Noise
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Solution Overview
Problem
Bandgap reference circuits with sub-1 μA operating current typically exhibit high noise, making it challenging to achieve both low noise and low power consumption in ultra-low power designs.
Innovation Solution
A bandgap reference circuit with a voltage generator, supply circuit, and control loop, featuring a transconductance amplifier and filter, which attenuates output noise and allows for precise current control, along with a voltage regulator to improve power-supply rejection ratio without increasing operating current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the operating current of the bandgap reference circuit is reduced to sub-1 μA level for ultra-low power design, then power consumption is improved, but noise increases significantly
Solution Approach 1:
The control loop is segmented into two functional parts: a transconductance amplifier for differential voltage amplification and a filter for noise attenuation. This segmentation allows each component to be optimized independently - the transconductance amplifier can operate at low current while the filter specifically targets noise reduction in the output signal.
Solution Approach 2:
The filter acts as an intermediary element between the transconductance amplifier and the output. It mediates the signal by passing the useful differential voltage information while attenuating the noise components, thereby resolving the contradiction between low current operation and low noise output.
2Object-generated harmful factors
If a filter is added to attenuate transconductance amplifier noise, then noise is reduced, but device complexity increases
Solution Approach 1:
The filter is designed to perform multiple functions: it attenuates noise from the transconductance amplifier, sets the bandwidth of the control loop, and works in conjunction with the voltage generator to maintain temperature compensation. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The filter's characteristics (such as cutoff frequency and attenuation level) are optimized to achieve noise reduction with minimal impact on the overall circuit performance. By carefully selecting filter parameters, effective noise attenuation is achieved without requiring complex filter topologies.
3Reliability
If a voltage regulator is added to improve power-supply rejection ratio, then PSRR is improved, but device complexity and operating current increase
Solution Approach 1:
The voltage regulator functionality is merged with the existing bandgap reference circuit structures. The supply circuit that provides current to the voltage generator is designed to also function as a voltage regulation stage, eliminating the need for a completely separate regulator circuit.
Solution Approach 2:
The supply circuit performs multiple functions: it provides the operating current to the voltage generator for temperature-compensated reference voltage generation, and simultaneously acts as a voltage regulator to reject power supply variations. This multi-functionality improves PSRR without adding separate dedicated regulator components.
Data Source
AI summary
A bandgap reference circuit and a method for providing a reference voltage are disclosed. In an embodiment a bandgap reference circuit includes a voltage generator including a first branch and a second branch and being configured to produce a reference voltage with a temperature coefficient lower than a given threshold, a supply circuit configured to provide a first current to the first branch and a second current to the second branch, and a control loop including a transconductance amplifier configured to provide an output signal representative of a difference between a first voltage of the first branch and a second voltage of the second branch and a filter coupled to an output of the transconductance amplifier, the filter configured to provide an output signal for controlling the first current and second current of the supply circuit.