Adaptive PA Bias Circuit for Millimeter-Wave 5G Linearity
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Solution Overview
Problem
In upcoming millimeter wave fifth generation (5G) communications systems, the efficiency of power amplifiers is challenging due to high frequency and bandwidth, along with high peak-to-average power ratios, making existing efficiency enhancement techniques difficult to apply.
Innovation Solution
An adaptive biasing circuit for power amplifiers that adjusts the bias level based on input signal amplitude, using a bias circuit with transistors and resistors configured to generate a bias voltage that increases with input magnitude, thereby reducing AM-AM distortion and improving output power and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If adaptive biasing is implemented to improve efficiency at lower output power levels, then power consumption is reduced, but device complexity increases due to additional transistors and control circuitry
Solution Approach 1:
The bias circuit dynamically adjusts the bias voltage level based on the instantaneous output power level of the amplifier. The circuit transitions from a static biasing approach to a dynamic one where the bias voltage automatically adapts to changing operating conditions, improving efficiency without requiring external control signals or complex digital processing.
Solution Approach 2:
The bias circuit is self-regulating and automatically adjusts its own bias voltage based on the amplifier's output power level. The circuit uses the amplifier's own operating conditions to control its biasing, eliminating the need for external control signals, microcontrollers, or complex feedback loops, thereby reducing overall system complexity while maintaining the efficiency benefits.
2Power
If bias voltage is increased to improve output power and OP1dB, then amplifier linearity improves, but power consumption increases
Solution Approach 1:
The bias voltage is dynamically adjusted based on the instantaneous output power level. At high output power levels where the amplifier operates in a more linear region, the bias voltage is increased to maintain linearity and improve OP1dB. At lower output power levels, the bias voltage is automatically reduced to decrease power consumption, thus achieving both goals simultaneously through dynamic adaptation rather than static compromise.
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 adaptive biasing circuit enhances the output referred 1 dB compression point (OP1dB) and saturated output power (Psat) while reducing power consumption, especially at lower output power levels, thereby improving the overall efficiency of power amplifiers in 5G systems.
Implementation Method 1
a second transistor (M2) configured to receive a first component of a differential input signal to the PA at a gate terminal. The second transistor has a drain terminal connected to the second circuit node and a source terminal connected to a second supply terminal
Data Source
AI summary
A bias circuit for a PA. A first transistor has its drain terminal and its gate terminal connected to a first circuit node and its source terminal connected to a first supply terminal, a first current source connected to the first circuit node, and a first resistor connected between the first and second circuit nodes. A second transistor receives a first component of a differential input signal to the PA at its gate terminal, has its drain terminal connected to the second circuit node and its source terminal connected to a second supply terminal, and a third transistor receives a second component of the differential input signal to the PA at its gate terminal, having its drain terminal connected to the second circuit node and its source terminal connected to a second supply terminal. The gates terminals of the second and third transistors are biased by a first voltage.