Diode-Coupled Transistor Reference Network for Low-Impedance ADC Signals
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Solution Overview
Problem
Pipelined analog-to-digital converter systems face challenges in generating accurate low-impedance reference signals, which are critical for high-speed and high-resolution signal processing, as errors in these signals can corrupt the final digital output and are susceptible to temperature, process, and supply variations.
Innovation Solution
The implementation of a reference network using a diode-coupled transistor with a backgate voltage control system, which maintains a constant output current and selectively alters the reference voltage, providing low-impedance and temperature-independent reference signals through a complementary common-drain output stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional reference signal generation is used in pipelined ADC systems, then the system can achieve high sample rates, but the reference signals suffer from high impedance and susceptibility to temperature, process, and supply variations
Solution Approach 1:
The patent changes the electrical parameters of the reference signal generation by using a diode-coupled transistor configuration with backgate voltage control. This alters the impedance characteristics and temperature dependence of the reference signals, transforming them from high-impedance, temperature-sensitive signals to low-impedance, temperature-stable signals that can support high-speed conversion without accuracy degradation
2Device complexity
If conventional reference networks are used, then the system structure remains simple, but the reference signals have high output impedance and are susceptible to variations
Solution Approach 1:
The patent introduces a diode-coupled transistor as an intermediary element between the reference voltage source and the output. This intermediary device, controlled by backgate voltage, acts as a buffer that isolates the reference signal from temperature and supply variations while maintaining low output impedance, thereby protecting the signal integrity without requiring complex compensation circuits
3Ease of manufacture
If standard transistor configurations are used for reference output, then the circuit is easy to manufacture, but the output impedance remains high and speed is limited
Solution Approach 1:
The patent modifies the transistor operating parameters by coupling the transistor in a diode configuration and applying backgate voltage control. This changes the transistor's effective resistance and response characteristics, enabling faster signal response and lower output impedance while maintaining compatibility with standard CMOS fabrication processes, thus achieving high speed without sacrificing manufacturability
Data Source
AI summary
Reference network embodiments are provided for use in pipelined signal converter systems. The network embodiments are fast and power efficient and they generate low-impedance reference signals through the use of at least one output transistor, a diode-coupled transistor coupled to the output transistor, and a controller. The controller is configured to provide a backgate voltage to the diode-coupled transistor to thereby establish a substantially-constant output current. The controller is further configured to provide a gate voltage to the output transistor to establish a reference voltage.