RF Attenuation Circuit With Diode Tuning for Low Phase Error
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Solution Overview
Problem
Existing RF attenuation circuits face challenges with high insertion loss, gain-to-phase errors, and large layout size, particularly in digital-step-attenuators (DSAs) used in analog beamformers.
Innovation Solution
The proposed attenuation circuit employs a series connection of diodes and resistors with a tuning inductor to minimize gain-to-phase errors and reduce layout size, utilizing a control signal to switch between attenuation and bypass modes, and incorporates an amplifier-inductor to compensate for diode capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional RF attenuation circuits are used, then attenuation function is provided, but insertion loss is high
Solution Approach 1:
The circuit dynamically switches between two operational modes: attenuation mode (when first-control-signal voltage exceeds second-control-signal voltage) and bypass mode (when first-control-signal voltage is lower than second-control-signal voltage). This dynamic switching eliminates the need for signal to pass through lossy attenuation components when attenuation is not required, thereby reducing insertion loss while maintaining signal quality.
Solution Approach 2:
The harmful attenuation function is extracted and made conditional. Instead of always being present, the attenuation function is only activated when needed based on control signal comparison. The bypass mode effectively removes the attenuation path from the signal flow, eliminating insertion loss during normal operation.
2Measurement precision
If conventional attenuation circuits are used, then attenuation is achieved, but gain-to-phase error is high
Solution Approach 1:
The circuit provides dynamic phase consistency by switching between attenuation and bypass modes based on control signal comparison. When in bypass mode, the signal path remains unchanged maintaining consistent phase. When attenuation is required, the phase response remains predictable and consistent with the attenuation mode design, thereby reducing gain-to-phase error.
Solution Approach 2:
The control signal comparison mechanism acts as an intermediary that determines the operational mode. By comparing the voltages of first-control-signal and second-control-signal, the circuit intelligently selects between attenuation and bypass paths, ensuring phase consistency is maintained through controlled switching rather than uncontrolled signal degradation.
3Area of stationary object
If conventional attenuation circuits are used, then attenuation function is provided, but layout size is large
Solution Approach 1:
The circuit merges the attenuation function with a comparator-based control mechanism into a single integrated structure. The first-control-signal and second-control-signal paths are combined with the attenuation components in a way that allows the same circuit elements to serve multiple functions: signal attenuation, mode control, and phase consistency maintenance, thereby reducing overall layout size.
Solution Approach 2:
The circuit components serve multiple functions simultaneously. The attenuation components not only provide signal attenuation but also participate in the control signal comparison mechanism. The switching mechanism serves both to control attenuation mode and to maintain phase consistency. This multi-functionality reduces the number of separate components needed, thereby reducing layout size.
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
The circuit achieves low insertion loss, low gain-to-phase error, and a compact layout by optimizing diode placement and using a tuning inductor, ensuring consistent phase response across modes.
Implementation Method 1
the attenuation circuit may further comprise a tuning-inductor connected in series between the connection-node and an AC-reference-node
Implementation Method 2
The amplifier-inductor may be configured to: provide some of the functionality of an amplifier that provides an output signal to the connection-node; and compensate for the off-capacitance of the first- and second-attenuation-diodes
Implementation Method 3
the attenuation circuit is in a bypass mode of operation when the first-control-signal has a lower voltage than the second-control-signal
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
An attenuation circuit comprising: a connection-node (212) for connecting to an RF connection; an isolation-capacitor (C3, 217) connected in series between the connection-node and an internal-node (215); a first-bias-resistor (Rbias, 218) connected in series between a first-control-node (V1, 213) and the internal-node; a second-bias-resistor (Rbias, 219) connected in series between the internal-node and a second-control-node (V2, 214); a first-attenuation-diode (D1, 220) connected in series between the first-control-node and the internal-node, wherein the anode of the first-attenuation-diode is closest to the first-control-node; a second-attenuation-diode (D2) connected in series between the internal-node and the second-control-node, wherein the anode of the second-attenuation-diode is closest to the internal-node; a first-decoupling-capacitor (C1, 222) connected in series between the first-control-node and the reference-node; and a second-decoupling-capacitor (C2, 223) connected in series between the second-control-node and the reference-node. Attenuation resistors may be connected in series to the diodes and an inductor for compensating the off-capacitances of the PIN diodes may be connected to the connection node. Further compensating diodes and capacitors may be connected to the attenuation diodes.