High Speed Serial Receiver AFE Calibration via On-Die DFT
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Solution Overview
Problem
High speed serial receiver performance is sensitive to unit-to-unit variations in analog frontend (AFE) and phase detector transfer functions, which are challenging to measure accurately and automatically due to their input data dependency and high speed signal requirements.
Innovation Solution
An on-die design-for-test (DFT) circuit is integrated within the receiver to characterize the transfer functions of the AFE and phase detector, using a multiplexer to select between data and test signals, a frequency modulator to adjust signal frequencies, and a phase interpolator to vary clock edges, allowing for precise measurement without disrupting normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional measurement methods are used for AFE and phase detector transfer functions, then measurement accuracy can be achieved, but special test equipment and high speed signal requirements are needed, increasing device complexity and cost
Solution Approach 1:
The receiver performs self-calibration by using its own internal resources (local oscillators, mixers, ADCs) to generate test signals and measure its own AFE and phase detector transfer functions, eliminating the need for external specialized test equipment
Solution Approach 2:
A digital signal processing chain acts as an intermediary to convert high speed analog measurements into manageable digital data, allowing standard digital processors to analyze transfer functions without requiring high speed analog measurement equipment
2Measurement precision
If input data dependent measurements are performed, then accurate transfer function characterization is possible, but special test equipment is required
Solution Approach 1:
The calibration circuit uses the same receiver components (AFE, mixers, ADCs) for both normal operation and calibration measurements, allowing the system to perform dual functions without requiring separate specialized test equipment
Solution Approach 2:
The system generates its own calibrated test signals using internal local oscillators and uses its own digital processing resources to analyze the results, making the measurement process self-contained and independent of external test equipment
3Measurement precision
If high speed signal measurements are performed for phase detector response, then accurate phase detector transfer function can be obtained, but extremely high speed signals are required
Solution Approach 1:
The patent replaces high speed analog signal measurement with digital signal processing. The phase detector output is captured by a standard speed ADC and processed digitally to extract phase information, eliminating the need for extremely high speed measurement equipment
Solution Approach 2:
A digital signal processing chain serves as an intermediary between the high speed phase detector output and the measurement system, converting high speed phase variations into lower speed digital data that can be processed by standard equipment
Data Source
AI summary
An apparatus is provided which comprises: an amplifier; a first slicer coupled to the amplifier; a de-serializer coupled to an output of the first slicer; a multiplexer which is operable to select one of data or a test signal for the amplifier; a filter coupled to an input of the multiplexer to provide test signal; and a frequency modulator coupled to the filter, wherein the frequency modulator is operable to modulate frequency of the test signal. An apparatus is also provided which comprises: an analog multiplexer having a first input to receive serial data, and a second input; an analog front-end (AFE) coupled to an output of the analog multiplexer; and a filter coupled to the second input of the analog multiplexer.