Group Delay Measurement for ADCs Using Spectral Phase Analysis
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Solution Overview
Problem
Existing methods for measuring group delay in signal conversion devices, such as ADCs, are limited by the need for complex equipment, calibration, and inability to measure across wide frequency ranges, especially for devices with analog inputs and digital outputs, leading to approximate correction of frequency responses.
Innovation Solution
A method using two sinusoidal signal sources at low and high frequencies, with amplitude limiting, to generate a test signal injected into a DUT, allowing simultaneous measurement of signal sideband components and low-frequency fundamental phases for precise group delay determination across a wide frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If VNA-based method is used for group delay measurement, then measurement can be performed with standard equipment, but it cannot measure devices with different input/output port types (e.g., ADCs) or frequency converters
Solution Approach 1:
The patent introduces an intermediary signal processing approach using Fourier transform analysis of the output signal spectrum. Instead of directly measuring phase shift with VNA, the method uses spectral analysis of the output signal to extract phase information, enabling measurement of devices with different input/output types while maintaining precision through mathematical transformation of the signal characteristics.
Solution Approach 2:
The patent changes the measurement parameter from direct phase shift (VNA method) to spectral phase analysis through Fourier transform. By transforming the measurement domain from time-frequency direct measurement to spectral domain analysis, the method becomes applicable to ADCs and frequency converters while preserving measurement accuracy through the mathematical relationship between time and frequency domains.
2Adaptability or versatility
If time domain pulse shape analysis is used, then group delay can be measured for ADCs, but expensive and complicated test equipment with calibration is required
Solution Approach 1:
The patent extracts only the essential measurement function from complex time domain pulse analysis equipment. Instead of using expensive picosecond pulse sources and high-resolution sampling scopes, the method extracts phase information directly from the spectral components of the output signal using Fourier transform, eliminating the need for specialized expensive equipment while maintaining measurement capability for ADCs.
Solution Approach 2:
The patent creates a simplified measurement approach that copies the essential measurement principle from time domain analysis but implements it in the frequency domain. By using spectral analysis of a continuous signal instead of pulsed signals, the method achieves the same measurement goal with standard equipment, effectively creating a simplified version of the complex time domain measurement system.
3Measurement precision
If frequency step is reduced for precise frequency response correction, then measurement accuracy improves, but measurement time increases
Solution Approach 1:
The patent performs preliminary spectral analysis of the output signal to identify all relevant frequency components and their phases in a single measurement. By using Fourier transform on the complete output waveform, the method obtains phase information for all frequency components simultaneously, eliminating the need for sequential frequency sweeping and reducing measurement time while maintaining precision for frequency response correction.
Data Source
AI summary
Measurement of group delay for a device under test (DUT). A test signal includes (i) a low frequency sine wave fLF, (ii) sine wave harmonics at a high frequency fHF, (iii) L pairs of sideband components at frequencies k·fHF±2·fLF, where k odd, and M pairs of sideband components at frequencies k·fHF±fLF, where k is even. At DUT output, (i) phase ϕLF at frequency fLF is measured, (ii) both sideband phase ϕright(k) at frequencies k·fHF+2·fLF and phase ϕleft(k) at frequencies k·fHF−2·fLF for odd k, are measured, and (iii) both sideband phases ϕright(k) at frequencies k·fHF+fLF and ϕleft(k) at frequencies k·fHF−fLF for even k, are measured. Group delay τk at frequencies k·FHF, are determined from: τk=(ϕright(k)−ϕleft(k)−4·ϕL)/(4·fLF) for k odd, and τk=(ϕright(k)−ϕleft(k)−2·ϕL)/(2·fLF) for k even.