Differential Step Attenuator With Leakage Compensation Paths
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Solution Overview
Problem
Existing radio frequency step attenuators, such as Pi-type and T-type attenuators, suffer from high insertion loss at lower attenuation modes and switch leakages at high frequencies, leading to reduced signal-to-noise ratio and poor linearity, which degrades frequency selectivity and attenuation levels.
Innovation Solution
A differential attenuator design with switched resistor networks and compensation paths that cross-couple to cancel parasitic leakages, using passive resistor networks for high linearity and a control circuit to generate control signals for the switched resistor networks, along with inductive compensation to extend bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Pi-type or T-type step attenuators are used, then attenuation steps of 6, 12, 18 and 24 dB can be achieved, but insertion loss becomes large when working at lower attenuation modes
Solution Approach 1:
The attenuator is divided into multiple independent attenuation units (first attenuation unit, second attenuation unit, third attenuation unit, fourth attenuation unit), each providing specific attenuation steps. This segmentation allows selective activation of units to achieve different attenuation levels while minimizing overall insertion loss by only activating necessary units.
Solution Approach 2:
The attenuator employs dynamic switching mechanisms where attenuation units can be selectively activated or deactivated based on required attenuation level. Control signals dynamically adjust which units are active, enabling the system to adapt insertion loss characteristics to match the required attenuation mode, thereby reducing unnecessary energy loss.
2Ease of operation
If Pi-type or T-type step attenuators are used, then attenuation functionality is provided, but switch leakages occur which damage attenuation levels at high frequencies during deep attenuation mode
Solution Approach 1:
Bootstrap capacitors are introduced as intermediary elements connected between the control signal input and specific nodes in the attenuation units. These capacitors act as mediators that equalize voltages across switch terminals, effectively eliminating switch leakages by ensuring both terminals of each switch experience identical voltage potentials, thereby preventing leakage currents that would compromise attenuation accuracy.
Solution Approach 2:
The bootstrap mechanism provides a feedback path where the control signal voltage is fed back through capacitors to the switch control terminals. This feedback ensures that the voltage difference across switch terminals remains zero during switching operations, automatically compensating for any leakage tendencies and maintaining reliable attenuation performance at high frequencies.
3Adaptability or versatility
If variable gain amplifier with capacitive attenuator and current-steering transconductance stages is used, then gain and attenuation can be achieved, but linearity becomes poor due to active devices
Solution Approach 1:
The invention replaces active electronic components (transconductance stages, capacitive attenuators) with passive resistor networks and switching mechanisms. By substituting active devices that introduce non-linearity with passive resistive elements and controlled switches, the system maintains gain and attenuation capabilities while significantly improving linearity and signal fidelity.
Solution Approach 2:
The attenuator achieves variable gain and attenuation by changing the resistance values in the resistor networks through selective switching, rather than using active transconductance stages. This parameter change approach using passive resistors maintains linear operation across different attenuation levels, avoiding the non-linearity inherent in active device-based solutions.
Data Source
AI summary
An attenuator for attenuating a signal is disclosed. The attenuator comprises a differential input port with a positive input node and a negative input node to receive the signal; and a differential output port with a positive output node and a negative output node to output the attenuated signal. The attenuator further comprises a first switched resistor network connected between the positive input node and the positive output node; and a second switched resistor network connected between the negative input node and the negative output node. Further a pair of compensation paths is connected to the first and second switched resistor networks for cancellation their parasitic leakages, where a first compensation path is connected between the positive input node and the negative output node, and a second compensation path is connected between the negative input node and the positive output node. The attenuator further comprises a control circuit to generate control signals for controlling the first and second switched resistor networks.