Line Driver Current Mirror Trimming for Output Impedance Matching
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Solution Overview
Problem
Existing line drivers face inaccuracies in output impedance due to manufacturing process variations and require high-voltage transistors for signal swing, which can conflict with design limitations and application requirements.
Innovation Solution
A line driver incorporating an adjustable current mirror array circuit that adjusts output impedance by trimming current ratios using control bits, allowing for precise impedance matching and enabling implementation with transistors of lower withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistor array with multiple switches and resistors is used to adjust output impedance, then impedance matching capability is improved, but manufacturing precision deteriorates due to resistance value drift from process variations
Solution Approach 1:
The patent changes the approach from adjusting impedance through resistor values to adjusting it through current ratios. The current mirror array uses controlled current sources where the impedance is determined by the ratio of currents (I1/I2) rather than by physical resistor values. This allows impedance adjustment without relying on precise resistor manufacturing, as current ratios can be controlled more accurately through digital-to-analog conversion and current mirror scaling.
2Power
If transistors with higher withstand voltage are used to handle large signal swing, then signal transmission capability is improved, but device complexity and design adaptability worsen due to conflicts with manufacturing process limitations
Solution Approach 1:
The patent segments the signal handling function between the current mirror array (which handles the large signal swing) and the impedance adjustment circuitry (which operates at lower voltages). The current mirror transistors are sized and configured to withstand the full signal swing, while the impedance control is achieved through current ratios rather than voltage-dependent resistor values. This allows the use of standard low-voltage transistors in advanced processes while maintaining large signal capability.
3Reliability
If a resistor array is used for impedance adjustment, then output impedance control is improved, but device complexity increases due to multiple switches and resistors required
Solution Approach 1:
The patent uses a current mirror array that replicates and scales reference currents to create the necessary current sources. Instead of using multiple physical resistors and switches, the impedance control is achieved by copying a reference current through multiple mirror transistors with different aspect ratios, allowing impedance adjustment through current ratio control rather than through a complex resistor network.
Data Source
AI summary
A line driver includes a first resistive component, a second resistive component, an operational amplifier and an adjustable current mirror array circuit. A first terminal of the second resistive component and the first resistive component are coupled to a node, and a second terminal of the second resistive component is coupled to an output terminal. The operational amplifier receives a common mode voltage through the first resistive component, and generates a first signal and a second signal according to the common mode voltage and an input signal. The adjustable current mirror array circuit generates a first current to the node and a second current to the output terminal in response to the first and second signals, and adjusts a ratio of the second current to the first current in response to multiple control bits so as to set an output impedance of the output terminal.