Chopper Voltage Reference with Cascode Protection Against Offset
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Solution Overview
Problem
Bandgap voltage references face challenges in overcoming manufacturing non-idealities and achieving low noise and stability due to variations in supply voltage and temperature, with existing solutions struggling to reduce residual offset voltages caused by clock feed-through and mismatch non-idealities.
Innovation Solution
A voltage reference circuit utilizing a chopper technique with a cascode arrangement and a low noise, low amplitude clock signal, implemented in both the error amplifier and bandgap circuits, to reduce low frequency noise and manufacturing mismatches, while protecting transistors from breakage by maintaining voltage outputs below the chopper circuit's breakage threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a chopper circuit is used to reduce low frequency noise and manufacturing mismatches, then measurement precision is improved, but the risk of transistor breakage increases due to voltage exceeding the breakage threshold
Solution Approach 1:
A voltage divider circuit comprising first and second resistors is introduced as an intermediary between the chopper circuit input and the voltage reference output. This voltage divider reduces the voltage amplitude presented to the chopper circuit, preventing transistor breakage while maintaining the noise-reduction benefits of chopping. The voltage divider acts as a buffer that protects the chopper circuit transistors from excessive voltage stress.
Solution Approach 2:
The invention changes the voltage amplitude parameter by using a low amplitude clock signal for the chopper circuit instead of a full swing clock signal. This parameter change reduces the peak voltage stress on chopper circuit transistors, preventing breakage while maintaining sufficient chopping effectiveness for noise reduction. The clock signal amplitude is specifically tuned to be below the breakage threshold of the chopper transistors.
2Power
If a high supply voltage is used to increase power handling capability, then power is improved, but the voltage reference stability deteriorates due to increased noise and offset voltages
Solution Approach 1:
The voltage divider circuit serves as an intermediary that decouples the high supply voltage from the sensitive chopper circuit. By placing the voltage divider between the high voltage supply and the chopper circuit input, the high power capability is maintained at the supply level while the chopper circuit operates at reduced voltage levels, preventing noise and offset voltage degradation.
Solution Approach 2:
The voltage divider provides beforehand cushioning by pre-reducing the voltage amplitude before it reaches the chopper circuit. This protective measure is built into the circuit architecture, cushioning the chopper circuit transistors from excessive voltage stress before it can cause breakage or performance degradation.
3Measurement precision
If the chopper circuit operates at full voltage amplitude to maximize noise reduction, then measurement precision is improved, but device complexity increases due to additional protection circuits
Solution Approach 1:
The voltage divider circuit performs multiple functions simultaneously: it reduces voltage amplitude to prevent transistor breakage, maintains impedance matching for optimal chopping performance, and provides biasing for the chopper circuit inputs. This multi-functionality achieves noise reduction without proportionally increasing device complexity.
Data Source
AI summary
In an embodiment, a voltage reference circuit is disclosed that includes a first transistor circuit that is configured to receive an external supply voltage as an input and to output a first voltage and a chopper circuit that is configured to receive a second voltage as an input and to output a voltage reference. The chopper circuit has a breakage threshold. The voltage reference circuit further includes a second transistor circuit that is configured to receive the first voltage as an input and to output the second voltage at a value that is less than or equal to the breakage threshold of the chopper circuit.