Bandgap Voltage Reference Circuit Using Switched Capacitor Charge Redistribution
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Solution Overview
Problem
Existing bandgap voltage circuits in integrated circuits require high supply voltages, large areas, and are prone to inaccuracies due to component mismatches, making them undesirable for generating temperature-independent reference voltages.
Innovation Solution
A reference voltage circuit using a bipolar junction transistor (BJT) and a switched capacitor circuit, which operates at a supply voltage less than 1.5 volts, generates a temperature-independent voltage by injecting different currents during different phases of a clock cycle and redistributes charges between capacitors to produce a buffered reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional bandgap voltage circuit uses two BJTs operating at different current densities to generate temperature-independent voltage, then temperature independence is achieved, but supply voltage requirement increases to 1.5V or higher
Solution Approach 1:
The patent replaces the traditional voltage-domain operation with charge-domain operation using switched capacitor circuits. Instead of using BJTs to generate voltages that are then processed, the invention uses capacitors to store and redistribute charges, with the BJT operating in a switched mode to transfer charge between capacitors. This fundamental substitution enables operation at lower supply voltages while maintaining temperature independence through charge redistribution rather than voltage generation.
Solution Approach 2:
The patent changes the operating parameters of the BJT from continuous analog operation to periodic switched operation synchronized with a clock signal. The BJT switches between different current densities during different phases of the clock cycle, enabling the generation of temperature-independent voltage at lower supply voltages through temporal modulation rather than spatial differentiation of current densities.
2Temperature
If traditional bandgap voltage circuit uses two BJTs with different current densities, then temperature-independent voltage is generated, but circuit area increases due to BJT matching requirements
Solution Approach 1:
The patent merges the functions of two separate BJTs into a single BJT by using temporal separation instead of spatial separation. The single BJT operates at different current densities during different phases of a clock cycle, with charges from these different operating conditions stored on separate capacitors. This merging reduces the area required for BJT matching while maintaining the temperature-independent voltage generation function.
Solution Approach 2:
The patent employs periodic switching of the BJT at different current densities synchronized with a clock signal. During different phases of the clock cycle, the BJT operates at different current densities and transfers charges to different capacitors. This periodic action enables a single BJT to perform the function previously requiring two BJTs, thereby reducing area while maintaining temperature independence.
3Temperature
If traditional bandgap voltage circuit uses two BJTs operating at different current densities, then temperature-independent voltage is achieved, but manufacturing accuracy decreases due to component mismatches
Solution Approach 1:
The patent combines the functions of two BJTs into one BJT that operates at different current densities at different times. This eliminates the need for precise matching between two separate BJTs, as only a single BJT is required. The temporal separation of operations allows the single BJT to generate the necessary charge differences without suffering from manufacturing mismatches between multiple devices.
Solution Approach 2:
The patent substitutes voltage-based BJT operation with charge-based capacitor operation. Instead of relying on precise voltage generation and processing from multiple BJTs, the system uses capacitors to store charges and switched capacitor circuits to process these charges. This substitution reduces sensitivity to BJT manufacturing variations and improves overall circuit accuracy.
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 solution reduces power consumption, saves area, and minimizes inaccuracies by generating a first-order temperature-independent voltage of about 1.2 volts, which can be dynamically fractioned for analog-to-digital conversion applications.
Implementation Method 1
a bipolar junction transistor (BJT) configured to receive a first current during a first phase of a clock cycle to generate a first base-emitter junction voltage; and receive a second current during a second phase of a clock cycle to generate a second base-emitter junction voltage
Implementation Method 2
a switched capacitor circuit configured to provide a reference voltage associated with the first base-emitter junction voltage and the second base-emitter junction voltage
Data Source
AI summary
An integrated circuit includes a reference voltage circuit. The reference voltage circuit includes a bipolar junction transistor (BJT) configured to receive a first current during a first phase of a clock cycle to generate a first base-emitter junction voltage, and receive a second current during a second phase of the clock cycle to generate a second base-emitter junction voltage. The reference voltage circuit includes a switched capacitor circuit configured to provide a reference voltage associated with the first base-emitter junction voltage and the second base-emitter junction voltage.