Parallel Current Converter Circuit for Wide Linear VGA Gain Control
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Solution Overview
Problem
Existing current converter circuits struggle to maintain a uniformly varying output over several orders of magnitude, failing to provide linear gain control for variable gain amplifiers (VGAs) in applications like RF transmitters.
Innovation Solution
A current converter circuit comprising first and second current converters with input and output branches, each featuring a diode-connected NPN transistor and MOS transistor, connected in series with a tuning voltage circuit and resistor, and an output transistor, which converts linear input current to exponential output current, and a summing output node to extend the linear range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single current converter is used, then the circuit complexity is low, but the linear gain control range is limited
Solution Approach 1:
The current converter is divided into multiple parallel current converters (first, second, third, and fourth current converters), each handling a specific segment of the overall gain control range. This segmentation allows the circuit to achieve a wider total linear gain control range by combining the outputs of individual converters, effectively extending the operational range without requiring a single overly complex converter design.
Solution Approach 2:
The parallel current converters are merged at a common output node, combining their individual output currents to produce a composite output that spans the extended gain control range. This merging approach allows the system to leverage the strengths of each individual converter segment while achieving a unified wide-range gain control function.
2Adaptability or versatility
If the gain control range is extended, then the versatility improves, but the uniformity of output variation deteriorates
Solution Approach 1:
Each parallel current converter is designed with specific local characteristics optimized for its designated gain control segment. The tuning resistors and transistor configurations are locally adjusted to ensure that each converter maintains uniform output variation within its specific operational range, thereby preserving overall uniformity across the extended total range.
Solution Approach 2:
The circuit employs dynamic compensation mechanisms where the parallel current converters are configured to dynamically share the gain control burden across different operating points. This dynamic allocation ensures that as the total gain control range is extended, each converter operates in its optimal region, maintaining uniform output variation characteristics throughout the extended range.
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 provides a wider linear gain control range for VGAs, maintaining consistent gain steps and improving linearity and noise performance, allowing operation beyond previous limits.
Implementation Method 1
a current converter circuit for converting a linear input current to an exponential output current... each of which comprises: an input current branch with an input current source connected in series with a tuning voltage circuit... an output current branch with an output transistor
Data Source
AI summary
The disclosure relates to a current converter circuit. Example embodiments include a current converter circuit (600) for converting a linear input current (Ictrl_lin) to an exponential output current (Ictrl_sum), the current converter circuit (600) comprising first and second current converters (601, 602), each of which comprises: an input current branch (6031, 6032) with an input current source (6041, 6042) connected in series with a tuning voltage circuit (6051, 6052) and a tuning resistor (6061, 6062) between a supply voltage line (607) and a common voltage line (608); and an output current branch (6091, 6092) with an output transistor (6101, 6102) having a collector connected to an output node (6111, 6112), a emitter connected to the common voltage line (608) and a base connected to the tuning voltage circuit (6051, 6052), wherein the output nodes (6111, 6112) of the first and second current converters (601, 602) are connected to a summing output node (612) of the current converter circuit (600)