RF-DAC Pulse-Width Control for Higher Amplitude Resolution
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Solution Overview
Problem
Conventional RF-DACs face challenges in achieving high amplitude resolution due to device mismatches and limitations in lithography, particularly in SAW-less and multi-radio systems, where traditional noise shaping methods are ineffective, leading to inaccurate RF output levels that fail to meet emission requirements in wireless connectivity and multi-core RF-SoC environments.
Innovation Solution
The integration of a pulse width modulator (PWM) driven transistor in a digitally-controlled power amplifier (DPA) to adjust the envelope of the RF carrier output, enhancing amplitude resolution by improving time-domain resolution and reducing quantization noise through incremental PWM techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional current-source based DAC structure is used for amplitude control, then the RF transmitter can be implemented, but the amplitude resolution is limited due to device mismatches and lithography constraints
Solution Approach 1:
The patent changes the control parameter from voltage/current amplitude to pulse width (time domain). By using PWM to control the duty cycle of the RF signal, the amplitude resolution is improved because time-domain control is less susceptible to device mismatches and lithography variations compared to traditional voltage-controlled DAC structures.
2Measurement precision
If ΣΔ dithering through noise shaping is applied to improve amplitude resolution, then the resolution can be enhanced, but the quantization noise is pushed to higher frequencies where emission requirements are difficult to satisfy
Solution Approach 1:
The patent uses periodic pulse width modulation to control the RF amplifier. By modulating the pulse width periodically and controlling the duty cycle, the amplitude information is encoded in the time domain without requiring noise shaping, thus avoiding the generation of high-frequency quantization noise that would violate emission requirements.
3Ease of operation
If straightforward PWM is used to achieve amplitude modulation, then the DC amplitude can be corrected, but the RF output level at the carrier frequency becomes inaccurate
Solution Approach 1:
The patent incorporates feedback mechanisms to calibrate and correct the RF output level. By monitoring the actual carrier frequency output and adjusting the PWM duty cycle accordingly, the system achieves accurate RF output levels while maintaining the simplicity of PWM control in the time domain.
Data Source
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AI summary
An integrated circuit includes a digitally-controlled power generation stage (3324) for converting an input signal to a radio frequency carrier, the digitally-controlled power generation stage (3324) comprising a plurality of selectable switching devices capable of adjusting an envelope of the radio frequency carrier; and a pulse width modulator generator (1302, 1508) arranged to generate a pulse width modulator control signal and operably coupleable to the plurality of selectable switching devices of the digitally-controlled power generation stage (3324). The pulse width modulator generator (1302, 1508) inputs the pulse width modulator control signal to a subset of the plurality of the selectable switching devices such that a pulse width modulator signal adjusts the envelope radio frequency carrier output from the digitally-controlled power generation stage (3324).