Cascode Current-Voltage Converter for Low-Distortion DAC Output
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Solution Overview
Problem
Current current-to-voltage converters in high fidelity amplifiers introduce harmonic and thermal distortion, delay, and intermodulation due to the use of operational amplifiers, which degrade the performance of digital-to-analog converters like the PCM 1792.
Innovation Solution
A current-voltage converter design incorporating a cascode stage that maintains a constant potential difference across constant current generators, eliminating the need for operational amplifiers and using current reflector circuits with measurement and reinjection mechanisms to manage parasitic capacitance effects, thereby reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If operational amplifier assembly is used for current-to-voltage conversion, then voltage gain is achieved, but harmonic and thermal distortion, delay and intermodulation are introduced
Solution Approach 1:
The patent removes the operational amplifier from the current-to-voltage conversion circuit, extracting the source of distortion. Instead of using an op-amp assembly, the invention employs a direct current reflector circuit with constant current sources that converts current to voltage without introducing harmonic and thermal distortion, delay and intermodulation
Solution Approach 2:
The patent introduces a cascode stage as an intermediary element between the constant current sources and the output. This cascode configuration acts as a mediator that provides voltage gain while maintaining the low distortion characteristics of the constant current sources, isolating the gain function from the conversion function
2Object-generated harmful factors
If cascode stage is added to maintain constant potential difference, then thermal distortion is reduced, but device complexity increases
Solution Approach 1:
The patent replaces complex operational amplifier circuits with a simpler constant current source configuration combined with a cascode stage. This substitution eliminates the need for feedback loops and complex compensation circuits while achieving the same thermal distortion reduction through the inherent properties of constant current operation
3Object-generated harmful factors
If current reflector circuit is used to eliminate operational amplifier, then distortion is reduced, but voltage amplitude is limited
Solution Approach 1:
The patent segments the circuit functions into distinct stages: a current reflector circuit for low-distortion current-to-voltage conversion, and a cascode stage for voltage amplitude enhancement. This segmentation allows each stage to optimize its specific function without compromising the other, achieving both low distortion and high voltage output
Data Source
AI summary
The invention relates to a current-voltage converter (22) having a current reflector, the input current comprising a fixed component and a variable component, which comprises: an input (24) for the current to be converted; an output (26) for the converted voltage; a current-to-voltage conversion resistor (36) arranged between the output (26) and ground, the input (24) being connected to the output (26) for circulating the current to be converted in the resistor (36); and a current reflector circuit (38) comprising two constant current sources (40, 42) each connected between the output (26) and a respective reference voltage (32, 34). Said converter (22) also has a cascade stage (44, 46) connected in series to each constant current generator (40, 42) to bring about a constant difference in potential at the terminals of each constant current generator (40, 42) regardless of the output voltage.