High Performance, Wideband RF Synthesizer with Integrated VCO
Created: Apr 25, 2016
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This reference design, as shown, is a wideband radio frequency synthesizer with an integrated voltage-controlled oscillator. This design utilizes the concept of Phase Locked Loop (PLL). This features the LMX2592 RF synthesizer, which is a low-noise, wideband RF PLL with integrated VCO. It supports frequency range from 20Mhz to 9.8GHz. The LMX2592 accepts input frequencies up to 1.4GHz, which combined with frequency dividers and programmable low noise multiplier allows flexible frequency planning.
This device is powered through a 3.3V supply. It supports 2 flexible differential outputs, but can also be configured as single-ended outputs. This accepts a wide range of input signal frequency from 5MHz to 1400MHz. After the input stage, there is a programmable OSCin doubler, a pre-R divider, a multiplier, and then a post-R divider for fractional N-divider values. The PLL phase detector, also known as phase frequency detector (PFD), compares the outputs of the post-R divider and N divider and generates a correction current with the charge pump corresponding to the phase error until the two signals are aligned in phase (the PLL is locked). The charge pump output goes through external components (loop filter) which turns the correction current pulses into a DC voltage applied to the tuning voltage (Vtune) of the VCO. The output frequency of the VCO is inversely proportional to the DC voltage present at the tuning voltage point on pin Vtune. The tuning range is 0 V to 2.5 V. The 0V generates the maximum frequency and 2.5 V generates the minimum frequency.
Applications of wideband RF PLL synthesizer includes FM demodulation, FSK demodulation, tone decoding, frequency multiplication, signal conditioning, clock synchronization, and frequency synthesis. Also, practical applications include RADAR, microwave backhaul, satellite communications, and high-performance clock source for high-speed converters.