1.1 GHz Variable Gain Amplifiers and Baseband Programmable Filters
The ADRF6518 is a matched pair of 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). The excellent matching between channels and their high spurious-free dynamic range over all gain and bandwidth settings make the ADRF6518 ideal for quadrature-based (IQ) communication systems with dense constellations, multiple carriers, and nearby interferers. The various amplifier gains, filter corners and other features are all programmable via a serial port interface (SPI) port.
The first VGA that precedes the filters offers 24 dB of continuous gain control with fixed gain options of 9 dB, 12 dB, and 15 dB, and sets a differential input impedance of 400 Ω. The filters provide a six-pole Butterworth response with 0.5 dB corner frequencies from 1 MHz to 63 MHz in 1 MHz steps. For operation beyond 63 MHz, the filter can be disabled and completely bypassed, thereby extending the −3 dB BW up to 1100 MHz. A wideband peak detector is available to monitor the peak signal at the filter inputs. The pair of VGAs that follow the filters each provides 24 dB of continuous gain control with fixed gain options of 12 dB, 15 dB, 18 dB, and 21 dB. The output buffers offer an additional option of 3 dB or 9 dB gain and provide a differential output impedance of less than 10 Ω. They are capable of driving 1.5 V p-p into 400 Ω loads at better than 65 dBc HD3. The output common-mode voltage defaults to VPS/2 and can be adjusted down to 900 mV via the VOCM pin. Independent, built-in dc offset correction loops for each channel can be disabled via the SPI if fully dc-coupled operation is desired. The high-pass corner frequency is determined by external capacitors on the OFS1 and OFS2 pins and the postfilter VGA gain.
The ADRF6518 operates from a 3.15 V to 3.45 V supply and consumes a maximum supply current of 400 mA. When fully disabled, it consumes <1 mA. The ADRF6518 is fabricated in an advanced silicon-germanium BiCMOS process and is available in a 32-lead, exposed pad LFCSP. Performance is specified over the −40°C to +85°C temperature range.
- Point-to-point and point-to-multipoint radios
- Baseband I/Q receivers
- Diversity receivers
- ADC drivers
This product has been released to the market. The data sheet contains all final specifications and operating conditions. For new designs, ADI recommends utilization of these products.
The ADRF6518-EVALZ is a full featured evaluation board designed to allow the user to easily evaluate all features of the ADRF6518. The evaluation board provides a USB interface for easy filter programming, input and output SMA connections with single ended setups for both channels (due to the use of baluns). There is an optional configuration for fully differential, AC or DC coupled signaling for the input and output signal paths if user desires. Easy access to the three analog gain pins and input and output common-mode control pins are done though a 5×2 header. Measuring the peak detector is easily achieved via a 2×1 header. Enabling the ADRF6518 is done with a jumper and header combination. All headers are labeled appropriately. Access to the +3.3 V/360 mA single supply is achieved with clip leads to the VPS and COM test points; it has a range from +3.15 V to +3.45 V. Easy split supply operation is achieved with the removal of one 0 Ω resistor and the use of the VPI test point. Nominal VPI voltage range is between +3.3 V and +5 V. This configuration is useful if the user wants to test a +5 V supply ADI IQ Demodulator with the ADRF6518-EVALZ in a DC coupled fashion. The ADRF6518-EVALZ board is a 4 layer FR4 board. Setting the filter's cutoff frequency, filter bypass mode, maximum digital gain settings, power mode, and the output offset correction loop enable are all achieved via the SPI port which can be programmed via the ADRF6518 USB software provided on the ADI webpage.
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