Synthesized RF Source Mute Circuit for Fast Turn-On Phase Stability
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Solution Overview
Problem
Existing synthesized signal sources, such as phase lock loops, experience phase disturbances and long settling times due to electromagnetic coupling and impedance changes when a mute amplifier is enabled, which is problematic for applications requiring rapid turn-on and zero phase variation, especially in integrated circuits with narrow loop bandwidths.
Innovation Solution
A fast turn on compensation system that differentially couples the mute amplifier to the RF output signal load and uses a dummy amplifier to maintain constant impedance and power supply current, with a mute controller managing the enabling and disabling of the amplifiers to minimize phase disturbances, and optionally includes a buffer amplifier for additional isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the mute amplifier is enabled quickly for fast turn on, then the turn on speed is improved, but phase disturbance increases and settling time lengthens
Solution Approach 1:
The dummy amplifier is enabled in advance before the mute amplifier to pre-establish the load conditions. This preliminary action ensures that when the mute amplifier is enabled, the power supply current remains relatively constant, preventing phase disturbance and enabling fast turn on without compromising phase stability
Solution Approach 2:
The dummy amplifier acts as an intermediary that absorbs the transient effects of enabling the mute amplifier. By maintaining a constant load on the power supply, it mediates between the fast switching requirement and the phase stability requirement, preventing current disturbances from affecting the VCO phase
2Speed
If the loop bandwidth is widened for fast settling, then the settling speed is improved, but the final phase offset changes causing long settling time
Solution Approach 1:
The invention changes the power supply current parameter by using the dummy amplifier to maintain constant current conditions. This parameter change allows the loop to settle quickly without the final phase offset error that normally occurs when loop bandwidth is dynamically adjusted, as the constant current eliminates the source of phase disturbance
3Device complexity
If the VCO and mute amplifier are placed close together on integrated circuit, then the device complexity is reduced, but electromagnetic coupling increases causing phase disturbance
Solution Approach 1:
The dummy amplifier serves as an electromagnetic intermediary that isolates the VCO from the mute amplifier's RF fields. By maintaining a constant load and being positioned between the VCO and mute amplifier, it reduces electromagnetic coupling effects while allowing close proximity integration, thus reducing device complexity without significant phase disturbance
Data Source
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Figure 1B
Figure 2
AI summary
A fast turn on compensation system for a synthesized signal source includes a synthesized signal source coupled to a power supply and configured to generate a phase stable radio frequency (RF) output signal. A mute amplifier is coupled to the synthesized signal source and the power supply. A dummy amplifier is coupled to the mute amplifier and the power supply. A mute controller is coupled to the mute amplifier and the dummy amplifier, the mute controller is responsive to an enable signal and configured to enable the dummy amplifier and disable the mute amplifier when no RF output signal is being generated and disable the dummy amplifier and enable the mute amplifier when the RF output signal is being generated such that total power supply current delivered to the synthesized signal source and the dummy amplifier or mute amplifier is approximately constant before, during, and after enabling the mute amplifier to reduce phase disturbance of the RF output signals.