Photodiode Bias Controller Using PWM Duty Cycle Modulation
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Solution Overview
Problem
High voltage bias circuits for optical transceivers and receivers require a large number of components and have limited resolution and power monitoring capabilities, making them complex and inefficient.
Innovation Solution
A high voltage bias circuit using a microprocessor with an on-chip PWM unit to generate pulse-width modulated pulses, reducing the number of components and enhancing resolution by modulating the duty cycle of the pulses to achieve a greater range of bias voltages, and integrating current monitoring within the processor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional high voltage bias circuits are used for APDs, then the required high reverse bias voltage (30-90V) can be achieved, but the circuit complexity increases with many components including external PWM chips, FET switches, inductors, diodes, capacitors, and current monitors
Solution Approach 1:
The patent combines multiple discrete circuit components (PWM generator, voltage regulator, current monitor) into a single integrated circuit chip. The IC includes all necessary transistors, resistors, capacitors, and control logic on one substrate, eliminating the need for external PWM chips, FET switches, inductors, diodes, and separate current monitor circuits while maintaining the full functionality of generating and regulating 30-90V reverse bias for APDs
Solution Approach 2:
The integrated circuit performs multiple functions simultaneously: it generates the high voltage bias, regulates the voltage to precise levels, monitors the APD current, and provides temperature compensation. This multi-functional design replaces what previously required separate dedicated components for each function, significantly reducing overall circuit complexity
2Measurement precision
If traditional high voltage bias circuits are used, then the basic biasing function is provided, but the resolution is limited and power monitoring capabilities are insufficient
Solution Approach 1:
The patent replaces traditional analog voltage regulation mechanisms with digital control techniques. The integrated circuit uses digital-to-analog converters and microcontroller-based control to achieve precise voltage regulation with resolution significantly finer than traditional analog methods. Power monitoring is achieved through digital sampling and processing of current signals, providing enhanced measurement precision while integrating all functionality into a single chip
3Power
If external components are used for biasing, then the circuit can provide high voltage output, but the overall circuit size increases and integration is reduced
Solution Approach 1:
The patent consolidates all high voltage generation components onto a single integrated circuit substrate. The IC includes voltage-gated current sources, switching transistors, energy storage capacitors, and control logic all integrated together, eliminating the need for discrete external components such as separate PWM chips, FET packages, inductors, diodes, and capacitor arrays, thereby dramatically reducing the overall circuit footprint while maintaining the ability to generate high output voltages
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 reduces the component count, improves resolution, and makes the circuits more compact, accurate, and cost-effective by leveraging software for current monitoring and voltage regulation, while achieving finer voltage control through modulated PWM techniques.
Implementation Method 1
When the FET Q1 is switched off, a voltage reversal is induced so that the energy stored in the inductor L1 is discharged, passes through the diode, and is transferred to the capacitor C1
Implementation Method 2
photodiodes are often included in optical transceivers and/or optical receivers for detecting the optical signals that are to be converted into electrical signals
Implementation Method 3
APDs use the avalanche phenomenon to produce an amplified electrical signal and thus are more suited for use in low, weak, or reduced light applications
Data Source
AI summary
A method of, and an apparatus for, biasing photodiodes used in optical receivers or optical transceivers includes an electronic circuit for generating a bias voltage for the photodiode and a processor having a pulse-width modulation unit that produces pulse-width modulated pulses at a predetermined number of duty cycle values M. The processor is coupled to the electronic circuit such that a magnitude of the bias voltage is dependent upon a duty cycle value of at least one of the pulse-width modulated pulses. Advantageously, the processor includes a program for modulating the pulse-width modulated pulses generated by the processor between two different duty cycle values such that a number of obtainable bias voltages is greater than M. The result is a significant reduction in the number of necessary components.