ALLGEMEINE BESCHREIBUNG

The ADL5387 is a broadband quadrature I/Q demodulator that covers an RF/IF input frequency range from 30 MHz to 2 GHz. With a NF = 13.2 dB, IP1dB = 12.7 dBm, and IIP3 = 32 dBm at 450 MHz, the ADL5387 demodulator offers outstanding dynamic range suitable for the demanding infrastructure direct-conversion requirements. The differential RF/IF inputs provide a wellbehaved broadband input impedance of 50 Ω and are best driven from a 1:1 balun for optimum performance.  Ultrabroadband operation is achieved with a divide-by-2 method for local oscillator (LO) quadrature generation. Over a wide range of LO levels, excellent demodulation accuracy is  achieved with amplitude and phase balances ~0.05 dB and ~0.4°, respectively. The demodulated in-phase (I) and quadrature (Q) differential outputs are fully buffered and provide a voltage conversion gain of >4 dB. The buffered baseband outputs are capable of driving a 2 V p-p differential signal into 200 Ω.  The fully balanced design minimizes effects from second-order distortion. The leakage from the LO port to the RF port is <−70 dBc. Differential dc-offsets at the I and Q outputs are <10 mV. Both of these factors contribute to the excellent IIP2 specifications > 60 dBm.  The ADL5387 operates off a single 4.75 V to 5.25 V supply. The supply current is adjustable with an external resistor from the BIAS pin to ground. The ADL5387 is fabricated using the Analog Devices, Inc., advanced silicon-germanium bipolar process and is available in a 24-lead exposed paddle LFCSP.

 

FEATURES

Operating RF frequency 30 MHz to 2 GHz

LO input at 2 × fLO 60 MHz to 4 GHz

Input IP3: 31 dBm at 900 MHz

Input IP2: 62 dBm at 900 MHz

Input P1dB: 13 dBm at 900 MHz

Noise figure (NF) 12.0 dB at 140 MHz 14.7 dB at 900 MHz

Voltage conversion gain > 4 dB

Quadrature demodulation accuracy Phase accuracy ~0.4° Amplitude balance ~0.05 dB

Demodulation bandwidth ~240 MHz

Baseband I/Q drive 2 V p-p into 200 Ω

Single 5 V supply

 

ANWENDUNGEN

QAM/QPSK RF/IF demodulators

W-CDMA/CDMA/CDMA2000/GSM

Microwave point-to-(multi)point radios

Broadband wireless and WiMAX

Broadband CATVs

 

ANWENDUNGSINFORMATIONEN

STROMVERSORGUNG

The nominal voltage supply for the ADL5387 is 5 V and is applied to the VPA, VPB, VPL, and VPX pins. Ground should be connected to the COM, CML, and CMRF pins. Each of  the supply pins should be decoupled using two capacitors; recommended capacitor values are 100 pF and 0.1 µF.

LOCAL OSCILLATOR (LO) INPUT

The LO port is driven in a single-ended manner. The LO signal must be ac-coupled via a 1000 pF capacitor directly into LOIP, and LOIN is ac-coupled to ground also using a 1000 pF capacitor. The LO port is designed for a broadband 50 Ω match and therefore exhibits excellent return loss from 60 MHz to 4 GHz. The LO return loss can be seen in Figure 24. Figure 50 shows the LO input configuration. The recommended LO drive level is between −6 dBm and +6 dBm. For operation below 50 MHz, a minimum LO drive level of 0 dBm should be used. The LO frequency at the input to the device should be twice that of the desired LO frequency at the mixer core. The applied LO frequency range is between 60 MHz and 4 GHz.

RF INPUT

The RF inputs have a differential input impedance of approximately 50 Ω. For optimum performance, the RF port should be driven differentially through a balun. The recommended balun is M/A-COM ETC1-1-13. The RF inputs to the device should be ac-coupled with 1000 pF capacitors. Ground-referenced choke inductors must also be connected to RFIP and RFIN (recommended value = 120 nH, Coilcraft 0402CS-R12XJL) for appropriate biasing. Several important aspects must be taken into account when selecting an appropriate choke inductor for this application. First, the inductor must be able to handle the approximately 40 mA of standing dc current being delivered from each of the RF input pins (RFIP, RFIN). (The suggested 0402inductor has a 50 mA current rating). The purpose of the choke inductors is to provide a very low resistance dc path to ground and high ac impedance at the RF frequency so as not to affect the RF input impedance. A choke inductor that has a selfresonant frequency greater than the RF input frequency ensures that the choke is still looking inductive and therefore has a more predictable ac impedance (jωL) at the RF frequency.