ADMV4540 K Band Quadrature Demodulator with Integrated Fractional-N PLL and VCO
The ADMV4540 is a highly integrated quadrature demodulator with 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, 5 dB, 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 done through the SPI.
The LNA output is then downconverted to baseband using an inphase 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 is capable of rejecting 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 their high spurious-free dynamic range (SFDR) over all 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 125 MHz, 250 MHz, and 500 MHz are all programmable via a serial peripheral interface (SPI). The filters provide a sixth-order Butterworth response with −3 dB corner frequencies of 141 MHz, 282 MHz, and 565 MHz. For operation beyond 565 MHz, the filter can be disabled and completely bypassed, thereby extending the −3 dB bandwidth up to 900 MHz.
The high dynamic range baseband output amplifiers of the ADMV4540 provide an overall nominal conversion gain of 57 dB. 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.
This feature rich device contains an integrated fractional-N phase-locked loop (PLL) and a low phase noise voltage controlled oscillator (VCO) that generates 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 50 MHz. Alternatively, the REFIN can be driven by an external single-ended frequency reference up to 100 MHz. The phase frequency detector (PFD) comparison frequency operates up to 100 MHz, which allows for continuous LO coverage from 17 GHz to 21.5 GHz in extremely fine steps.
The ADMV4540 operates on a 3.3 V supply with less than 3.2 W of total power dissipation. It is available in a 48-terminal, RoHS compliant, 7 mm × 7 mm LGA package with an exposed paddle. The ADMV4540 can operate over the −40℃ to +85℃ temperature range on a + 3.3 V power supply.
- Satellite communications
Features and Benefits
- Fractional-N synthesizer with low phase noise VCO
- K band quadrature demodulator
- Programmable via 4-wire SPI
- RF operating frequency range: 17 GHz to 22 GHz
- LO internal frequency range: 17 GHz to 21.5 GHz
- Double sideband noise figure: 5 dB at maximum conversion gain
- Output integrated phase noise, 1 kHz to 10 MHz: <1°
- Maximum conversion gain of >50 dB
- Conversion gain control range of >50 dB
- IM3 of −54 dBc at −30 dBm composite input level, ΔfRF = 1 MHz
- 3 baseband, SPI-selectable LPFs with corner frequencies of: 125 MHz, 250 MHz, and 500 MHz on each baseband path