Self-Biased OTA Reference Circuit Reduces PVT Variation
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Solution Overview
Problem
Existing voltage-to-current converters using operational transconductance amplifiers (OTAs) require complex constant-gm bias circuits and separate startup circuits, leading to increased device area and power consumption, with bias current variations of up to ±50% across process, voltage, and temperature (PVT) due to transistor and resistor variations.
Innovation Solution
The implementation of self-biased OTAs with a startup current generator circuit that provides a startup current proportional to the bias current, using a p-channel metal-oxide-semiconductor field effect transistor (PMOS) and a resistor, which eliminates the need for constant-gm bias circuits and reduces component count, allowing the OTA to self-bias once the voltage feedback net reaches a threshold, thereby minimizing PVT variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant-gm bias circuit is used to generate bias current for the OTA, then the bias current can be maintained, but the device area and power consumption increase
Solution Approach 1:
The patent extracts and eliminates the separate constant-gm bias circuit from the traditional voltage-to-current converter architecture. Instead of using a dedicated bias circuit, the invention uses the output current of the converter itself to self-bias the OTA through a feedback path, thereby removing the unnecessary components that consume area and power while maintaining bias current stability
Solution Approach 2:
The patent merges the bias current generation function into the main voltage-to-current conversion path. The OTA's bias current is generated from its own output current through a feedback mechanism, combining what were previously separate functions (conversion and biasing) into a unified self-biasing architecture that reduces overall device complexity
2Reliability
If a separate startup circuit is used to initialize the OTA, then the circuit can start up properly, but the device area and power consumption increase
Solution Approach 1:
The patent removes the separate startup circuit from the traditional architecture. Instead of using a dedicated startup circuit that consumes power and occupies area, the invention relies on the self-biasing mechanism where the OTA naturally initializes through its own operation and feedback path, eliminating the need for external startup assistance
Solution Approach 2:
The OTA performs its own startup initialization through the self-biasing mechanism. The feedback path from the output current to the bias current input allows the circuit to automatically establish proper operating conditions without requiring external startup circuits, making the system self-sufficient
3Quantity of substance
If traditional bias circuits are used, then bias current can be generated, but bias current variations of up to ±50% occur across PVT
Solution Approach 1:
The patent implements a feedback mechanism where the output current of the voltage-to-current converter is fed back to the bias current input of the OTA. This feedback loop automatically adjusts the bias current to maintain a precise relationship with the output current, compensating for PVT variations and reducing bias current precision errors from ±50% to ±15%
Solution Approach 2:
The patent changes the parameter relationship between bias current and output current from a fixed traditional relationship to a dynamically adjusted relationship through feedback. The bias current is no longer a fixed parameter but varies in response to output current changes, maintaining precision across different process, voltage, and temperature conditions
Data Source
AI summary
A device may include a voltage-to-current converter circuit having an operational transconductance amplifier (OTA), the voltage-to-current converter circuit for generating a bias current that is proportional to a reference voltage at a reference voltage input port of the OTA, and a bias current feedback path for providing the bias current to a bias current input port of the OTA. The device may further include a startup current generator circuit coupled to the bias current input port of the OTA, the startup current generator circuit controllable to provide a startup current to the bias current input port during a startup of the device and to be deactivated after the startup of the device.