LNA Bias Circuit Using One OTA and a Replica Cascode
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Solution Overview
Problem
Existing bias circuits for low noise amplifiers (LNAs) consume significant power and area due to the use of two operational transconductance amplifiers (OTAs), particularly in lower gain modes, and lack efficient control over bias current with process, voltage, and temperature variations.
Innovation Solution
A bias circuit for LNAs is implemented using a single operational transconductance amplifier (OTA) with a replica circuit to generate bias voltages, reducing power consumption and circuit area while maintaining control over bias current and gain, employing a cascode transistor and gain transistor configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two operational transconductance amplifiers (OTAs) are used in the bias circuit, then good control over bias current is achieved, but power consumption and circuit area increase significantly
Solution Approach 1:
The patent combines the functions of two separate OTAs into a single OTA by integrating the bias generation for both the cascode transistor and gain transistor through one operational amplifier. This merging reduces power consumption and circuit area while maintaining bias current control through the replica circuit mechanism.
Solution Approach 2:
The patent employs a replica circuit that copies the amplifier core's transistor structure to generate accurate bias voltages. The replica circuit includes a replica cascode transistor and replica gain transistor that mirror the main amplifier's transistors, allowing the single OTA to properly bias both devices without needing two separate OTAs.
2Reliability
If two operational transconductance amplifiers (OTAs) are used in the bias circuit, then good control over bias current is achieved, but circuit area increases significantly
Solution Approach 1:
The patent merges the bias control functions into a single OTA, eliminating the need for two separate operational amplifiers. This consolidation significantly reduces the circuit area occupied by the bias network while maintaining effective bias current control through the integrated replica circuit.
Solution Approach 2:
The single OTA in the patent performs multiple functions: it biases both the cascode transistor and the gain transistor, and it controls both the first and second current sources. This multi-functionality reduces the overall circuit area compared to using two separate OTAs.
3Use of energy by stationary object
If a single operational transconductance amplifier (OTA) is used with a replica circuit, then power consumption and circuit area are reduced, but control over bias current may be compromised
Solution Approach 1:
The replica circuit copies the exact transistor structure and operating conditions of the amplifier core, allowing the single OTA to accurately sense and control the bias current. The replica cascode transistor and replica gain transistor mirror the main devices, ensuring that the bias voltages generated are precisely what is needed for optimal performance.
Solution Approach 2:
The single OTA operates with feedback from the replica circuit to automatically adjust and maintain the correct bias current. The OTA senses the voltage drops across the current sources and adjusts its output voltages to maintain proper biasing, providing robust control despite using only one OTA.
4Ease of operation
If existing bias circuits are used, then biasing is provided, but linearity deteriorates under varying process, voltage, and temperature conditions
Solution Approach 1:
The patent dynamically adjusts bias parameters through the OTA's ability to vary output voltages based on feedback from the replica circuit. This allows the bias conditions to adapt to changing process, voltage, and temperature conditions, maintaining linearity across different operating environments.
Data Source
AI summary
An amplifier circuit includes an amplifier core having a cascode transistor and a gain transistor, a bias circuit coupled to the amplifier core, the bias circuit comprising: a first current source, a second current source, an operational transconductance amplifier (OTA), a bias cascode transistor pair having a bias cascode transistor and a bias gain transistor, and a replica circuit coupled to the first current source and to the second current source.