Programmable Delay in Transmitters to Reduce VCO Pulling
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Solution Overview
Problem
Transmitter circuits face frequency shifts due to signal coupling from power amplifiers to phase locked loop (PLL) circuits, disrupting the intended frequency output.
Innovation Solution
A transmitter circuit with a programmable delay circuit that adjusts the propagation delay between the PLL and power amplifier signals to maintain consistent operational characteristics, minimizing frequency shifts by compensating for signal coupling effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power amplifier drives the antenna with a high power signal, then the transmission capability is improved, but the signal coupling to the PLL circuit causes frequency shifts that worsen frequency stability
Solution Approach 1:
The patent applies preliminary action by measuring and storing the operational characteristics of the PLL circuit at different power amplifier output levels before actual transmission. The system pre-determines compensation values that are applied during transmission to counteract the expected frequency shifts, thus maintaining frequency stability even when the power amplifier is driving at high power levels
Solution Approach 2:
The patent implements parameter changes by adjusting the operational characteristics of the PLL circuit based on the measured impact of different power amplifier output levels. The system modifies parameters such as voltage control oscillator tuning or phase detector settings to compensate for the frequency shifts caused by signal coupling, thereby maintaining accurate frequency output across different transmission power levels
2Measurement precision
If the propagation delay between PLL and power amplifier is adjusted, then the frequency shift compensation is improved, but the circuit complexity increases due to the programmable delay circuit
Solution Approach 1:
The patent applies dynamics by implementing a programmable delay circuit that can dynamically adjust the propagation delay between the PLL circuit and power amplifier based on operating conditions. The delay value is programmably controlled to optimize frequency shift compensation for different transmission scenarios, allowing the system to adapt rather than requiring fixed complex circuitry for all conditions
Data Source
AI summary
A transmitter circuit includes a phase locked loop circuit, having one or more operational characteristics indicative of an operating state of the phase locked loop circuit. The phase locked loop circuit is configured to generate a frequency signal. The transmitter circuit also includes a power amplifier configured to selectively drive an antenna with a drive signal according to the frequency signal, and a programmable delay circuit configured to controllably extend a propagation delay between the frequency signal and the drive signal of the power amplifier. The programmable delay circuit is programmed such that a first value of a particular operational characteristic of the phase locked loop circuit is substantially equal to a second value of the operational characteristic of the phase locked loop circuit. The first value is measured with the power amplifier not driving the antenna. The second value is measured with the power amplifier driving the antenna.