Dynamic Bias Control for Shockline Sampler Isolation
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Solution Overview
Problem
High-frequency Vector Network Analyzers (VNA) face challenges in accuracy due to intermodulation-product generation and inadequate channel-to-channel isolation, which are not adequately addressed by existing shockline-based sampler technologies, leading to measurement errors and increased system complexity and cost.
Innovation Solution
Applying a bias voltage to nonlinear transmission lines (NLTLs) in shockline-based samplers to dynamically control the falling-edge compression and RF bandwidth, allowing for selective activation or deactivation of channels to reduce spurious generation and enhance isolation, thereby improving the dynamic range without the drawbacks of prior methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shockline-based samplers are used in VNA receivers, then intermodulation-product generation is reduced and channel isolation is improved, but spurious responses are generated due to partial reflection at the sampler's RF port
Solution Approach 1:
The patent applies a bias voltage to the nonlinear transmission line to dynamically control the falling-edge compression and RF bandwidth of the shockline sampler. By adjusting the bias voltage, the system optimizes the compression ratio and bandwidth parameters to reduce spurious response generation while maintaining channel isolation performance. This parameter control allows the sampler to operate in an optimized state that minimizes intermodulation products and spurious signals.
2Reliability
If additional isolation components are added to reduce spurious generation, then channel isolation is improved, but system complexity and cost increase
Solution Approach 1:
The patent extracts and addresses the source of spurious responses directly at the shockline sampler by applying bias voltage control to reduce spurious generation at its origin. This approach eliminates the need for additional external isolation components that would otherwise be required to suppress spurious responses, thereby reducing system complexity and cost while maintaining effective channel isolation.
3Object-generated harmful factors
If bias voltage is applied to NLTL to control falling-edge compression, then RF bandwidth is dynamically controlled and spurious generation is reduced, but device complexity increases
Solution Approach 1:
The bias voltage control mechanism serves multiple functions simultaneously: it controls the falling-edge compression ratio, adjusts the RF bandwidth, and reduces spurious response generation. By using a single bias control system to achieve multiple performance objectives, the patent avoids the need for separate control circuits for each function, thereby minimizing the increase in device complexity while achieving comprehensive performance optimization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for enhanced channel-to-channel isolation and reduced spurious responses, minimizing the need for additional isolation components, thus reducing system complexity and cost while maintaining or improving the dynamic range of the receiver.
Implementation Method 1
The shockline-based samplers use nonlinear transmission lines (NLTLs) 151-154 which can receive a continuous wave (CW) local oscillator (LO) signal from the signal generator through the power splitter. Each NLTL compresses the falling edge of the LO signal creating a series of sharp step-function-like wavefronts, or shocks.
Implementation Method 2
The pulse forming network of the sampler can then be used to differentiate these shocks, resulting in electrical pulses that are used as to gate the sampler.
Implementation Method 3
An RF signal, shown as fRF, can be either provided through DUT 205 from another port or reflected from the DUT 205 and received at the RF port of Sampler 2. The reflected RF signal can mix with LO products in Sampler 2, generating a spurious signal, fspur, shown as comprising |mfRF±nfLO±pfIF| where m, n, and p are integers.
Data Source
AI summary
Shockline-based samplers of a vector-network analyzer (VNA) have enhanced dynamic range by using a dynamic bias network applied to the non-linear transmission lines (NLTLs) or shocklines. The bias voltage applied to the NLTL provides direct control over the falling-edge shockline compression, and thus the insertion loss and overall RF bandwidth of the sampler. Alternating between a forward bias voltage to turn off a shockline sampler when it is not needed and thereby reducing spurious generation and improving isolation can be alternatively applied with a reverse bias voltage to turn on the shockline sampler in a normal operation mode. By measuring the shockline output and providing feedback in the reverse-bias mode, the bias voltage can be dynamically adjusted to significantly increase the performance of the NLTL based sampler. In the presence of a strong positive bias voltage, the incoming LO and its harmonics experience large ohmic losses thus preventing gating pulses from forming in the shockline. The ohmic losses enable strong isolation between the LO sampling channels and will increase spectral purity at the VNA test ports.