Chopper-Stabilized Attenuator for Precise Current Sense Loops
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Solution Overview
Problem
Current sense loops in high-voltage applications face challenges in achieving precision due to resistor mismatch errors in attenuators, which are exacerbated by the need for larger resistors to reduce error, leading to increased chip real estate requirements.
Innovation Solution
Embedding an input chopper within the attenuator circuit to reduce resistor mismatch errors by using low-voltage resistors, which are more sensitive to mismatch but occupy less space, thereby minimizing the error contribution from these resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If larger resistors are used in the attenuator to reduce resistor mismatch errors, then measurement precision is improved, but chip area increases
Solution Approach 1:
The patent changes the voltage parameter of the resistors from high-voltage to low-voltage, allowing the use of smaller resistor values while maintaining the same attenuation ratio. This parameter change enables reduced chip area while achieving the same or better measurement precision through the chopper stabilization technique.
Solution Approach 2:
The patent introduces chopper circuits as intermediary elements between the attenuator inputs and outputs. These chopper circuits modulate the signals and use capacitive coupling to transfer signals between high-voltage and low-voltage domains, enabling the use of low-voltage resistors in a high-voltage attenuator application.
2Area of stationary object
If low-voltage resistors are used in the attenuator, then chip area is reduced, but resistor mismatch error increases
Solution Approach 1:
The chopper circuits serve as intermediaries that modulate the low-voltage resistor signals and transfer them to the high-voltage domain through capacitive coupling. This intermediary mechanism allows low-voltage resistors to function effectively in a high-voltage attenuator without suffering from mismatch errors.
Solution Approach 2:
The patent transforms the operating voltage parameter of the resistors from high-voltage to low-voltage, which allows using smaller physical resistors that occupy less chip area. The chopper stabilization technique compensates for the potential increase in mismatch error by dynamically adjusting the signal path.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves a 0.01% ΔV error reduction in resistor mismatch, resulting in a significant area savings of approximately 3.7 mm² for the attenuator resistors while maintaining precision, with the remaining error primarily from high-voltage resistors being minor.
Implementation Method 1
a chopper amplifier, i.e., an amplifier with a modulator at the input and a demodulator at the output
Implementation Method 2
a first capacitor having a first terminal coupled to a node between the first chopper and the first attenuator and a second terminal coupled to a second node, and a second capacitor having a first terminal coupled to a third node between the second chopper and the second attenuator and a second terminal coupled to a fourth node
Data Source
AI summary
A current sense loop includes an attenuator circuit, which has an embedded input chopper circuit, and an amplifier circuit, which has an output chopper circuit. The embedded input chopper has a first chopper input that is coupled to a first attenuator input, a first chopper output that is coupled to a first attenuator output, a second chopper input that is coupled to a second attenuator input, and a second chopper output that is coupled to a second attenuator output. An amplifier has a first input coupled to the first attenuator output and a second input coupled to the second attenuator output. An NFET has a gate coupled to the amplifier output, a source coupled to a ground plane, and a drain coupled to the second attenuator input.