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Analog Devices Inc. ADMV4540 K-Band Quadrature Demodulator is a highly integrated quadrature demodulator with an integrated synthesizer ideally suited for next-generation K-band satellite communication. The RF front end of the ADMV4540 consists of two Low Noise Amplifier (LNA) paths, each with an optimal cascaded, 5dB, double-sideband noise figure at maximum gain while minimizing external components. The dual paths allow support for antenna polarization. Selection of the LNA path can be made through the Serial Peripheral Interface (SPI).
The LNA output of the ADMV4540 is downconverted to baseband using an in-phase and quadrature (I/Q) mixer. The I/Q mixer output is then fed into fully differential low noise and low distortion programmable filters and Variable Gain Amplifiers (VGAs). Each channel can reject large, out-of-band interferers while reliably boosting the wanted signal, thus reducing the bandwidth and resolution requirements on the analog-to-digital converters (ADCs) of the system. The excellent matching between channels and the high spurious-free dynamic range (SFDR), overall gain, and bandwidth settings make the ADMV4540 ideal for satellite communication systems with dense constellations, multiple carriers, and nearby interferers.
The three filter corners of 125MHz, 250MHz, and 500MHz are programmable via a Serial Peripheral Interface (SPI). The filters provide a sixth-order Butterworth response with -3dB corner frequencies of 141MHz, 282MHz, and 565MHz. For operation beyond 565MHz, the filter can be disabled and completely bypassed, thereby extending the -3dB bandwidth up to 900MHz.
The high dynamic range baseband output amplifiers of the ADMV4540 provide an overall nominal conversion gain of 57dB. The three baseband voltage variable attenuator (VVA) pins (VCTRL_BBVVAx) of the ADMV4540 can be used for automatic gain control (AGC), giving the ADMV4540 a wide RF input dynamic range.
The ADMV4540 includes an integrated fractional-N phase-locked loop (PLL) and a low phase noise voltage-controlled oscillator (VCO). These integrated functions generate the necessary on-chip local oscillator (LO) signal for the two double balanced I/Q mixers, eliminating the need for external frequency synthesis. The VCO utilizes an internal automatic calibration routine that allows the PLL to select the necessary settings and lock.
The reference input (REFIN) to the PLL of the ADMV4540 employs a differentially excited crystal oscillator at 50MHz. Alternatively, the REFIN can be driven by an external single-ended frequency reference up to 100MHz. The phase-frequency detector (PFD) comparison frequency operates up to 100MHz, which allows for continuous LO coverage from 17.0GHz to 21.5GHz in extremely fine steps.
The Analog Devices Inc. ADMV4540 K-Band Quadrature Demodulator is available in a 48-terminal, RoHS compliant, 7.0mm × 7.0mm LGA package with an exposed paddle. The device operates on a 3.3V supply with less than 3.2W of total power dissipation.
