Bandgap Reference Circuit With Chopper Noise Reduction
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Solution Overview
Problem
Existing bandgap reference circuits suffer from output noise and temperature variability, especially in low-power applications, requiring large resistors or high-capacity capacitors that are impractical for on-chip integration, and result in increased power consumption or silicon area.
Innovation Solution
The bandgap reference circuit employs source degeneration on current mirrors and chopper circuits to reduce output noise and improve temperature stability, utilizing cascode configurations and chopper stabilization to minimize systematic and random mismatches, thereby reducing the need for large filtering capacitors and minimizing silicon area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large value resistors are used to generate output voltage in current-mode bandgap references, then the output voltage can achieve desired value (e.g., 1.2V), but the output noise increases proportionally with resistance value
Solution Approach 1:
The patent employs chopper stabilization technique where a switching signal periodically modulates the bandgap circuit operation. This periodic action converts low-frequency noise (flicker noise) to higher frequency components that can be filtered out, thereby reducing output noise while maintaining the desired output voltage level without requiring large resistors
Solution Approach 2:
The patent introduces chopper stabilization circuits as intermediary elements between the bandgap reference core and the output. These intermediary circuits include modulators and demodulators that process the reference signal, effectively separating the noise from the useful signal and reducing output noise without affecting the output voltage generation
2Object-generated harmful factors
If resistor value is decreased to reduce output voltage noise, then noise decreases, but current value must be increased to maintain output voltage, resulting in higher power consumption
Solution Approach 1:
Chopper stabilization uses periodic switching to modulate the circuit operation, enabling noise reduction through frequency transformation rather than through resistor value changes. This allows maintaining low noise performance without increasing current and power consumption
Solution Approach 2:
The patent changes the operating parameters of the bandgap circuit by introducing time-varying modulation through chopper stabilization. This parameter change enables the circuit to achieve low noise performance through dynamic operation rather than static parameter adjustments like increasing current
3Object-generated harmful factors
If a low-pass filter with large capacitor value is added at the output to decrease output voltage noise, then noise is reduced, but the capacitor integration on-chip becomes impractical
Solution Approach 1:
Chopper stabilization transforms the noise reduction approach from passive filtering (requiring large capacitors) to active modulation. By periodically modulating the signal and using synchronous demodulation, the circuit achieves noise reduction without requiring large on-chip capacitors for low-pass filtering
4Object-generated harmful factors
If large area transistors are used to reduce low-frequency noise in current-mode bandgap, then flicker noise is reduced, but the silicon area of the bandgap significantly increases
Solution Approach 1:
Chopper stabilization uses periodic modulation to shift flicker noise to higher frequencies where it can be more easily filtered. This technique reduces flicker noise without requiring large transistor areas, as the noise reduction is achieved through frequency transformation rather than increasing device size
Solution Approach 2:
The chopper stabilization circuits act as intermediary elements that process the bandgap signal and remove flicker noise through modulation and demodulation. This intermediary processing reduces flicker noise without requiring the bandgap transistors themselves to be large in area
Data Source
AI summary
A bandgap reference circuit includes a complimentary to absolute temperature (CTAT) current generator providing a CTAT current with a source degeneration resistor, and a proportional to absolute temperature (PTAT) current generator providing a PTAT current. The PTAT current generator includes a first branch with a source degeneration resistor, a first p-type metal-oxide semiconductor (PMOS) transistor, and a first n-type metal oxide semiconductor (NMOS) transistor, a resistor, and a diode-connected transistor. A second branch includes a source degeneration resistor, a second PMOS transistor, a second NMOS transistor, and a diode-connected transistor. The second branch coupled to the first branch in a current mirror configuration. A chopper circuit alternately couples drain terminals of the first and second PMOS transistors in series to the remainder of their respective branches.