Zero-IF Transceiver Architecture to Suppress VCO Pulling
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Solution Overview
Problem
Conventional zero-IF transmitter arrangements face challenges with VCO-pulling due to signal coupling between the radio frequency power amplifier and the tank circuit, leading to deteriorated spectral purity and reduced ability to handle interfering signals, especially at high operating frequencies.
Innovation Solution
The VCO frequency is set to (n+1/2) times the transmitter output frequency, using a fractional frequency divider with a division factor of 3/2 to generate mixer signals with a relative phase difference of 2π/3 radians, avoiding integer relations between VCO frequency and transmitter output harmonics, thus minimizing VCO-pulling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a zero-IF transmitter arrangement is used, then the transmitter structure is simplified and power consumption is reduced, but VCO-pulling occurs due to signal coupling between the RF power amplifier and the tank circuit, deteriorating spectral purity
Solution Approach 1:
The patent changes the frequency relationship parameter between VCO and transmitter output from an integer ratio to a non-integer ratio (specifically f_VCO/f_RF = n + 1/2 where n is an integer). This parameter change breaks the integer relationship that causes VCO-pulling, thereby reducing the harmful coupling effect while maintaining the zero-IF architecture's power efficiency
Solution Approach 2:
The patent introduces asymmetry in the frequency relationship by using a non-integer ratio (n + 1/2) instead of a symmetric integer ratio. This asymmetric frequency relationship prevents the harmonics of the transmitter output from aligning with the VCO frequency, thereby suppressing VCO-pulling while maintaining system simplicity
2Device complexity
If the VCO frequency is set to an integer multiple of the transmitter output frequency, then the system design is simplified, but VCO-pulling is exacerbated due to resonant coupling at harmonic frequencies
Solution Approach 1:
The patent modifies the frequency ratio parameter from an integer (n) to a non-integer (n + 1/2), which maintains design simplicity while fundamentally changing the frequency relationship to avoid resonant coupling. This parameter adjustment prevents harmonics from aligning with the VCO frequency, thereby suppressing VCO-pulling without significantly increasing design complexity
3Manufacturing precision
If conventional zero-IF architecture is used with integer frequency relationship, then spectral purity deteriorates due to VCO-pulling, but changing to non-integer frequency relationship requires fractional frequency division
Solution Approach 1:
The patent changes the frequency division ratio from an integer to a fractional value (specifically 3/2 when n=1/2). This fractional frequency division enables the VCO to operate at a non-integer multiple of the transmitter output frequency, thereby suppressing VCO-pulling and improving spectral purity while adding only moderate complexity through the use of a fractional frequency divider
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
This approach effectively suppresses VCO-pulling, maintaining spectral purity and improving the transmitter's ability to handle interfering signals, while allowing for a more flexible design of RF amplifiers and reducing power consumption.
Implementation Method 1
A voltage controlled oscillator (VCO) is used to generate a mixer signal at a frequency that is (n+1/2) times the transmitter output frequency
Implementation Method 2
A fractional frequency divider is used to divide the VCO output frequency by a factor of 3/2, generating mixer signals at the desired radio frequency
Implementation Method 3
A transmitter output signal is generated by combining an in-phase radio frequency signal generated by mixing an in-phase baseband signal with a first radio frequency mixer signal, and an alternative-phase radio frequency signal generated by mixing an alternative-phase baseband signal with a second radio frequency mixer signal
Data Source
AI summary
An output signal is generated for transmission in a telecommunications systems. This may involve generating an in-phase radio frequency signal by mixing an in-phase baseband signal with a first radio frequency mixer signal; and generating an alternative-phase radio frequency signal by mixing an alternative-phase baseband signal with a second radio frequency mixer signal. An output signal for transmission is generated by combining the in-phase radio frequency signal with the alternative-phase radio frequency signal, wherein the output signal has a frequency, fRF. The first and second radio frequency mixer signals are generated by generating a voltage controlled oscillator (VCO) output signal having a frequency, fVCO, such thatfVCO=(n+12)·fRF,wherein n=1, 2, 3, . . . ; and generating one or more fractional frequency divided signals from the VCO output signal, wherein each of the one or more fractional frequency divided signals has a frequency equal to fRF.