Variable Gain Amplifier Temperature Compensation Without Large Feedback Loops
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Solution Overview
Problem
Variable gain amplifiers face challenges with temperature drift due to changes in resistor behavior, leading to non-linearity and requiring large circuitry for feedback loops and digital control, which consume space and power.
Innovation Solution
A temperature compensation circuit using a constant current source and a temperature-dependent current source with an operational amplifier to generate an offset signal, adjusting the gain control signal to counteract temperature-induced gain variations, with transistors having negative or positive temperature coefficients to maintain linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous feedback loop is used to monitor output swing and adjust gain setting, then temperature drift is compensated, but circuitry area and power consumption increase due to large feedback loop time constant and fine gain control requirements
Solution Approach 1:
The patent extracts the temperature compensation function from the complex continuous feedback loop and implements it through a separate temperature compensation circuit that generates a compensation signal based on temperature sensing. This separates the temperature compensation task from the main feedback loop, reducing the burden on the feedback circuitry and allowing for simpler design with smaller area requirements.
Solution Approach 2:
The temperature compensation circuit performs preliminary action by sensing temperature changes and generating compensation signals in advance, before the temperature drift significantly affects the amplifier performance. This proactive approach allows the system to pre-adjust for temperature variations rather than continuously reacting to output swing changes, reducing the complexity of the feedback loop.
2Reliability
If direct biasing of NPN amplifier devices with positive temperature coefficient current is used, then gain temperature compensation is achieved, but common mode voltage changes which affect linearity and maximum allowable amplifier swing
Solution Approach 1:
The patent introduces an intermediary approach by using a temperature compensation circuit that generates a compensation signal, which is then combined with the gain control signal through a summing junction. This intermediary compensation signal adjusts the gain to counteract temperature effects without directly biasing the NPN devices, thereby avoiding common mode voltage changes and preserving linearity and amplifier swing capabilities.
3Ease of operation
If gain levels are defined based on resistor values, then amplifier gain is controlled, but temperature drift occurs because resistor behavior changes with temperature
Solution Approach 1:
The patent applies parameter changes by introducing a temperature-dependent compensation signal that dynamically adjusts the gain control based on temperature conditions. Instead of relying solely on fixed resistor values that drift with temperature, the system changes the effective gain parameter by adding the compensation signal, which varies with temperature to counteract the resistor drift and maintain stable gain performance.
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 effectively compensates for temperature-induced gain variations, maintaining linearity and reducing the need for extensive circuitry, thereby improving amplifier performance and efficiency.
Implementation Method 1
A temperature dependent current source is configured to generate a temperature dependent current which is used to create a temperature dependent voltage
Implementation Method 2
An operational amplifier is configured to compare the constant voltage to the temperature dependent voltage and generate an offset signal which varies over temperature
Data Source
AI summary
An amplifier with temperature compensation where the amplifier has transistors configured to amplify a received signal to create an amplified signal. The amplifier gain changes over temperature. A gain control circuit, connected to the amplifier, that adjusts the amplifier gain responsive to a gain control signal. A temperature compensation circuit includes numerous elements. A constant current source that generates a constant current which is used to create a constant voltage. A temperature dependent current source that generates a temperature dependent current which is used to create a temperature dependent voltage, such that the temperature dependent current source has an inverse temperature dependance as compared to the amplifier. An operational amplifier compares the constant voltage to the temperature dependent voltage and generates an offset signal which varies over temperature. A gated buffer is configured to receive the offset signal and responsive thereto, selectively modify the gain control signal.