Logarithmic Current-Voltage Circuit With On-Chip Temperature Compensation
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Solution Overview
Problem
Conventional logarithmic current-to-voltage conversion circuits face instability due to varying temperature coefficients, limiting their performance and integration capabilities, as they often require off-chip temperature compensation systems.
Innovation Solution
A logarithmic current-to-voltage conversion circuit with integrated temperature compensation, comprising a logarithmic current-to-voltage conversion buffer unit, a positive temperature coefficient compensation unit, and a self-heating unit, which uses a reference circuit and adjustable resistors to correct temperature coefficients and maintain signal stability across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If off-chip temperature compensation system is used, then temperature stability is improved, but device complexity increases and monolithic integration cannot be achieved
Solution Approach 1:
The patent merges the temperature compensation function with the logarithmic conversion circuit by integrating the compensation circuit into the same chip. The compensation circuit uses a reference BJT and operational amplifier to generate a compensation voltage that counteracts temperature drift, achieving both temperature stability and monolithic integration without requiring external components.
Solution Approach 2:
The patent introduces a reference BJT and operational amplifier as intermediary elements that sense temperature variations and generate compensating signals. These intermediaries detect the temperature drift through the reference transistor's Vbe voltage changes and use the operational amplifier to produce a compensating voltage that offsets the drift in the main conversion circuit.
2Ease of operation
If conventional operational amplifier and BJT architecture is used, then logarithmic signal conversion is achieved, but temperature coefficient variation causes poor signal stability
Solution Approach 1:
The patent implements a feedback mechanism where the compensation circuit continuously monitors temperature variations through the reference BJT and adjusts the compensation voltage accordingly. The operational amplifier in the compensation circuit amplifies the difference between the reference Vbe and the main conversion Vbe, generating a real-time compensating signal that feeds back to stabilize the output against temperature drift.
Solution Approach 2:
The patent exploits the temperature dependence of the BJT's base-emitter voltage (Vbe) parameter. By measuring the Vbe voltage of a reference BJT at a known current, the circuit detects temperature changes and uses this information to generate a compensating voltage that counteracts the temperature-induced parameter variations in the main conversion transistor, thereby stabilizing the overall conversion characteristic.
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
The solution enables complete in-chip temperature compensation, allowing for monolithic integration and significantly improving the stability of the output signal across temperature variations, as demonstrated by simulation results.
Implementation Method 1
an architecture formed by an operational amplifier and a bipolar junction transistor (BJT) is used to implement a logarithmic signal conversion from current (I) to voltage (V)
Implementation Method 2
A temperature coefficient is reflected by a difference value ΔVbe between an output of the basic logarithmic circuit and an output of the reference circuit
Implementation Method 3
a temperature coefficient of (R1+R0)/R2 is corrected by adjusting a value of the adjustable resistor R1
Implementation Method 4
The self-heating unit is integrated at a bottom of the logarithmic current-to-voltage conversion circuit
Data Source
AI summary
Provided is a logarithmic current-to-voltage conversion circuit having a temperature compensation function. The circuit includes a logarithmic current-to-voltage conversion buffer unit, a positive temperature coefficient compensation unit and a self-heating unit. The logarithmic current-to-voltage conversion buffer unit is provided with a reference circuit consistent with a basic logarithmic circuit. A temperature coefficient is reflected by a difference value ΔVbe between an output of the basic logarithmic circuit and an output of the reference circuit. The positive temperature coefficient compensation unit is provided with a voltage-to-current conversion circuit at a first stage and a current mirror at a second stage and outputs a voltage Vout through an resistor R2. The positive temperature coefficient compensation unit is connected to ΔVbe. The voltage-to-current conversion circuit is provided with a resistor R0 and an adjustable resistor R1 connected in series, where a temperature coefficient of (R1+R0)/R2 is corrected by adjusting a value of the adjustable resistor R1.