Digital Step Attenuator Switching to Prevent RF Overshoot
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Solution Overview
Problem
Digital step attenuators (DSAs) experience transient overshoot during state transitions, which can lead to RF signals exceeding safe power levels, potentially damaging circuit components due to unpredictable changes in total attenuation during the transition period.
Innovation Solution
The solution involves controlling the DSA units to switch from an insertion state to an attenuation state first, ensuring transient attenuation reaches a maximum value before switching to an insertion state, thereby preventing overshoot by forcing undershoot, using a series cascade of attenuation units and control signals to manage the transition states of switches within the attenuator network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If switches in digital step attenuator are changed state simultaneously to adjust attenuation level, then the attenuation can be adjusted quickly, but transient overshoot occurs causing RF signals to exceed safe power levels
Solution Approach 1:
The patent applies preliminary action by first transitioning switches to the attenuation state before transitioning them to the insertion state. This staged approach ensures that attenuation is established before insertion, preventing transient overshoot while maintaining relatively fast adjustment speeds. The control unit implements this by generating control signals that sequence the state changes of multiple switches.
2Object-affected harmful factors
If switches are transitioned slowly from insertion state to attenuation state to prevent overshoot, then transient overshoot is reduced, but the attenuation adjustment speed decreases
Solution Approach 1:
The patent resolves this contradiction by using preliminary action with a specific sequence: first transition to attenuation state, then to insertion state. This staged transition prevents overshoot without requiring slow single-step transitions, thereby maintaining acceptable adjustment speed while eliminating the harmful transient effect.
3Device complexity
If multiple switches are changed state at the same time to achieve desired attenuation level, then the control is simple, but the total attenuation changes unpredictably during transition
Solution Approach 1:
The patent applies preliminary action by implementing a two-stage transition sequence that maintains attenuation stability. The control unit first generates signals to transition all switches to the attenuation state, establishing a known intermediate attenuation level. Then it transitions switches to the insertion state to reach the final desired level. This predictable sequencing eliminates unpredictable attenuation changes while keeping control logic relatively simple.
Data Source
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AI summary
Apparatus and methods for controlling overshoot in digital step attenuators are disclosed. By configuring a multi-bit DSA such that an attenuation control block changes a plurality of control signals in a manner preventing a series cascade of attenuation units from having a transient attenuation value less than an initial and final value of attenuation, an overshoot condition can be prevented. Control signals transition the attenuation units to a first state of attenuation before they transition attenuation units to a second state of insertion.