ADRF6518ACPZ-R7 datasheet(27/36 Pages) AD

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Preliminary Technical Data

ADRF6518

Rev. PrA | Page 27 of 36

COMMON-MODE BYPASSING

The ADRF6518 common-mode pins, VICM/AC and VOCM,

must be decoupled to ground. At least one low inductance,

surface-mount ceramic capacitor with a value of 0.1 μF must be

used to decouple the common-mode pins.

SERIAL PORT CONNECTIONS

The ADRF6518 has a SPI port to control the gain and filter band-

width settings. Data can be written to the internal 15-bit register

and read from the register. It is recommended that low-pass RC

filtering be placed on the SPI lines to filter out any high frequency

glitches. See Figure 74, the evaluation board schematic, for an

example of a low-pass RC filter.

ENABLE/DISABLE FUNCTION

To enable the ADRF6518, the ENBL pin must be pulled high.

Driving the ENBL pin low disables the device, reducing current

consumption to approximately 9 mA at room temperature.

GAIN PIN DECOUPLING

The ADRF6518 has three analog gain control pins: VGN1,

VGN2, and VGN3. Use at least one low inductance, surface-

mount ceramic capacitor with a value of 0.1 μF to decouple

each gain control pin to ground.

PEAK DETECTOR CONNECTIONS

The ADRF6518 has peak detector output on the VPK pin, with

a scaling of 1 V/V pk differential at filter inputs. The bigger

peak of the two channels reported. The peak detector time-

constant can be changed with a resistor from the RAVG pin to

VPS. Leave the RAVG pin open for the longest time-constant

(hold time). RAVG resistor range is ∞ to 1 kΩ.

To reset the peak detector, pull the SDO/RST pin high for 25 ns

or longer. Logic levels are VLOW < 0.8 V, VHIGH > 2 V.

ERROR VECTOR MAGNITUDE (EVM) PERFORMANCE

Error vector magnitude (EVM) is a measure used to quantify

the performance of a digital radio transmitter or receiver by

measuring the fidelity of the digital signal transmitted or

received. Various imperfections in the link, such as magnitude

and phase imbalance, noise, and distortion, cause the

constellation points to deviate from their ideal locations.

In general, a receiver exhibits three distinct EVM limitations

vs. received input signal power. As signal power increases, the

distortion components increase.

•

At large enough signal levels, where the distortion compo-

nents due to the harmonic nonlinearities in the device are

falling in-band, EVM degrades as signal levels increase.

•

At medium signal levels, where the signal chain behaves

in a linear manner and the signal is well above any notable

noise contributions, EVM has a tendency to reach an opti-

mal level determined dominantly by either the quadrature

accuracy and IQ gain match of the signal chain or the

precision of the test equipment.

•

As signal levels decrease, such that noise is a major con-

tributor, EVM performance vs. the signal level exhibits

a decibel-for-decibel degradation with decreasing signal

level. At these lower signal levels, where noise is the

dominant limitation, decibel EVM is directly proportional

to the SNR.

EVM TEST SETUP

The basic setup to test EVM for the ADRF6518 consisted of an

Agilent MXG M5182B Vector Signal Generator used as a signal

source and a Agilent DSO7104B oscilloscope used to sample the

signal while connected to a computer running Agilent 89600 VSA

software to calculate the EVM of the signal. The M5182B IQ

baseband differential outputs drove the ADRF6518 inputs. The

I and Q outputs of the ADRF6518 were loaded with 400 Ω

differential impedances and connected differentially to two

AD8130 differential amplifiers to convert the signals into single-

ended signals. The single-ended signals were connected to the

input channels of the VSA.

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