Digital Attenuator Circuit for High Dynamic Range Pre-Power Amplifier
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Solution Overview
Problem
Current pre-power amplifiers for wireless communication standards like WCDMA and CDMA2000 face challenges in achieving high dynamic range and efficient power consumption, with existing designs being inadequate for the stringent signal-to-noise ratio and power efficiency requirements.
Innovation Solution
A digital attenuator circuit is integrated into the pre-power amplifier to extend its dynamic range, allowing for precise control of current output by splitting it between the load and AC ground, enabling the amplifier to achieve over 100 dB of dynamic range without the need for a DAC and minimizing noise degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable gain pre-power amplifier is used to control transmit signal amplitude, then the dynamic range is improved, but noise degradation increases and signal to noise ratio deteriorates
Solution Approach 1:
The patent replaces the traditional analog variable gain amplifier with a digital attenuator consisting of switchable current sources and current mirrors. This substitution of digital switching mechanisms for analog gain control eliminates the noise degradation inherent in analog variable gain amplifiers while achieving the required dynamic range through digital control of current magnitudes.
Solution Approach 2:
The patent segments the current output into multiple discrete current sources that can be independently switched. By dividing the total current into segments controlled by individual switches and using current mirrors to replicate these segments, the system achieves fine-grained control over the output amplitude, enabling high dynamic range without the noise problems of continuous analog adjustment.
2Use of energy by moving object
If digital CMOS pre-power amplifiers are designed for low dynamic range standards, then power consumption is reduced, but they cannot meet high dynamic range requirements of WCDMA and CDMA2000
Solution Approach 1:
The patent implements a dynamic current control scheme where multiple current sources are switched based on the required output amplitude. The system dynamically adjusts which current sources are active and their relative weights through digital control, allowing the same hardware to adapt to different dynamic range requirements and power consumption constraints of various wireless standards.
Solution Approach 2:
The patent changes the operational parameters of the current sources by adjusting their weight factors through digital control. By varying the effective current magnitude of each source and their combination, the system can achieve different output power levels and dynamic ranges while maintaining efficient power consumption, accommodating both low-power and high-dynamic-range requirements.
3Ease of operation
If traditional transmit chain architectures with variable gain buffers are used, then signal amplitude control is achieved, but overall power consumption increases to at least 50 mW
Solution Approach 1:
The patent merges the functions of the variable gain buffer and the digital attenuator into a single integrated current control stage. By combining the current sources, switches, and control logic into one unified digital attenuator module, the system eliminates the need for separate analog gain control circuitry, thereby reducing overall power consumption while maintaining full signal amplitude control capability.
Data Source
AI summary
A novel digital attenuator circuit and associated pre-power amplifier (PPA) that substantially increases the dynamic range of the amplifier. Increased dynamic range is achieved by placing a digital current attenuator circuit at the output of the pre-power amplifier so that the minimum possible current output of the transistor switch array of the PPA can be further attenuated. The attenuator functions to split the current between the load and the power supply VDD (i.e. AC ground) based on device ratio that is controlled digitally via an input power control word. The digital attenuator is constructed as a segmented digitally controlled matrix or cell array comprising at least a pass and bypass matrix or array. The pass matrix controls the amount of current output from the PPA while the bypass matrix controls the amount of current shorted to the AC ground (i.e. power supply). By varying the number of transistors on or off in each matrix, the power output of the PPA can be easily and accurately controlled.