RF Amplifier Power Control via Cascode Gate Voltage Adjustment
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Solution Overview
Problem
CMOS amplifier circuits are sensitive to variations in supply voltage, leading to fluctuations in output power, which is undesirable in applications requiring constant envelope RF signal amplification, especially in GSM amplifiers where large PMOS pass devices are needed to prevent IR drops and ensure accurate power control, resulting in increased die size and cost.
Innovation Solution
A cascode configuration of transistors is used where the gate voltages of cascoded transistors are adjusted based on the varying supply voltage to maintain nominal output power, eliminating the need for large PMOS pass devices by compensating for voltage variations through gate voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large PMOS pass devices are used in LDO regulator to prevent IR drops and ensure accurate power control, then power control accuracy is improved, but die size increases
Solution Approach 1:
The patent changes the control parameter from supply voltage (Vdd) to gate voltage (Vg) of the cascoded transistors. By adjusting Vg dynamically, the output power is controlled without requiring large pass devices, thus maintaining power control accuracy while reducing die size.
Solution Approach 2:
The patent introduces gate voltage control as an intermediary mechanism between the LDO regulator and the power amplifier output. Instead of directly controlling output power through large pass devices, the gate voltage of cascoded transistors serves as an intermediary to achieve precise power control with smaller devices.
2Adaptability or versatility
If supply voltage varies, then power consumption flexibility is improved, but output power fluctuates
Solution Approach 1:
The patent implements a feedback mechanism where the varying supply voltage is detected and used to dynamically adjust the gate voltage of the cascoded transistors. This feedback loop compensates for supply voltage variations, maintaining stable output power while allowing flexible power consumption adaptation.
Solution Approach 2:
The patent makes the gate voltage dynamic rather than fixed, allowing it to adapt in real-time to supply voltage variations. This dynamic adjustment enables the system to maintain output power stability while accommodating flexible power consumption requirements.
3Temperature
If constant quiescent current is used to desensitize amplifier performance, then temperature stability is improved, but output power becomes sensitive to supply voltage changes
Solution Approach 1:
The patent changes the control parameter from supply voltage to gate voltage of cascoded transistors. This parameter change allows the amplifier to maintain constant quiescent current for temperature stability while becoming insensitive to supply voltage variations, as output power is now controlled by gate voltage rather than supply voltage.
Data Source
AI summary
Systems, methods and apparatus for efficient power control and/or compensation with respect to a varying supply voltage of an RF amplifier for amplification of a constant envelope RF signal are described. A reduction in a size of a pass device of an LDO regulator is obtained by removing the pass device of the LDO regulator from a main current conduction path of the RF amplifier. Power control and/or compensation is provided by varying one or more gate voltages to cascoded transistors of a transistor stack of the RF amplifier according to a power control voltage. Various configurations for controlling the gate voltages are presented by way of a smaller size LDO regulator or by completely removing the LDO regulator. In a case where a supply voltage to the transistor stack varies, such as in a case of a battery, a compensation circuit is used to adjust the power control voltage in view of a variation of the supply voltage, and therefore null a corresponding drift/variation in output power of the RF amplifier.