Translinear Variable Gain Amplifier for Linear-in-dB Range
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing variable gain amplifier circuits face limitations in achieving a linear-in-dB gain curve, which restricts the range of linear-in-dB operation and maximum gain value, especially when used in systems with logarithmic signal detection.
Innovation Solution
A variable gain amplifier circuit comprising two common base transistors and an additional transistor forming a translinear loop, where the current through the second transistor is copied to the additional transistor, compensating for non-ideal transfer functions and enhancing the linear-in-dB range and maximum gain value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional variable gain amplifier circuits are used, then the circuit can operate with variable gain, but the linear-in-dB range is limited and maximum gain value is restricted
Solution Approach 1:
The amplifier circuit is segmented into multiple functional blocks: a first variable gain amplifier stage with exponential gain control, a second variable gain amplifier stage with complementary exponential control, and a summation stage. Each stage operates with a specific gain range, and their combined output achieves an extended linear-in-dB range while maintaining high maximum gain capability.
Solution Approach 2:
The invention changes the control parameter from a single exponential control voltage to a combination of two exponential control voltages with opposite signs. The first stage is controlled by +vctrl while the second stage is controlled by -vctrl, allowing the circuit to maintain linear-in-dB behavior across a wider gain range and achieve higher maximum gain values.
2Ease of operation
If a single exponential gain control is used, then the gain can be varied, but the loop gain becomes dependent on signal level
Solution Approach 1:
The invention implements a feedback mechanism where the output of the logarithmic detector is fed back to control the gain of the variable gain amplifier. The feedback control voltage is processed through exponential conversion circuits that generate complementary control signals for the two amplifier stages, ensuring that the overall loop gain remains constant and independent of signal level.
Solution Approach 2:
The circuit uses asymmetric control where the first and second variable gain amplifier stages are controlled by exponential voltages of opposite signs (+vctrl and -vctrl). This asymmetric control strategy ensures that as one stage's gain increases, the other stage's gain decreases in a complementary manner, maintaining constant loop gain while providing wide gain adjustment range.
Data Source
AI summary
A variable gain amplifier circuit (300) comprising a first transistor (310) and a second transistor (312); and an additional transistor (320). The first transistor (310) and second transistor (312) are arranged as common base transistors. The additional transistor (320) is configured to provide part of a translinear loop with the first (310) and second transistors (310). A current through the conduction channel of the first transistor (310) is configured to contribute to an output of the variable gain amplifier circuit current. The circuit (300) is configured such that a current through the conduction channel of the second transistor (312) is copied to the additional transistor (322).