Wideband LO PLL Synthesizer with Simple Interface to Quadrature Demodulators (CN0245)
The circuit, shown in Figure 1, highlights the ease of interfacing theADF4350wideband synthesizer with integrated VCO with theADL5380andADL5387wideband I/Q demodulators. In this circuit, the ADF4350 provides the high frequency, low phase noise local oscillator (LO) signal to the wideband I/Q demodulator.
This circuit configuration offers quite a few benefits that make it an attractive solution in applications requiring quadrature mixing down to baseband or to an intermediate frequency.
The ADF4350 offers RF differential outputs and, likewise, the ADL5380/ADL5387 accept differential inputs. This interface offers both ease of use and performance advantages. The differential signal configuration provides common-mode noise reduction and even order cancellation of the LO harmonics, which maintains the quadrature accuracy of the I/Q demodulators. Additionally, the output power level of the ADF4350 matches the input power requirements of the quadrature demodulators very well. As a result, an LO buffer is not necessary.
The ADF4350 outputs cover a wide frequency range from 137.5 MHz to 4400 MHz. The ADL5387 frequency range spans from 50 MHz to 2 GHz, and the ADL5380 covers the higher frequency range from 400 MHz to 6 GHz. Between the ADL5380 and ADL5387 the RF input range can span from 50 MHz to 6 GHz. Therefore, the two chip circuit configuration as shown in Figure 1 offers coverage of a wide frequency range from 50 MHz to 4400 GHz.
Figure 1. Simple Interface Between the ADF4350 PLL Synthesizer and the ADL5380 or ADL5387 Quadrature Demodulator (Simplified Schematic: All Connections and Decoupling Not Shown)
Схемы и диаграммы
Быстро получите общее представление о схемотехнике решения