ADRF6520ACPZ-R7 datasheet(23/29 Pages) AD

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Data Sheet

ADRF6520

Rev. 0 | Page 23 of 29

The most challenging scenario in terms of dynamic range is the

presence of a large out of band blocker accompanying a weaker

in-band wanted signal. In this case, the maximum input level is

dictated by the blocker and its inclination to cause distortion.

After filtering, the weak wanted signal must be amplified to the

desired output level, possibly requiring the maximum gain on

VGA2. In such a case, both the distortion limits associated with

the blocker at the input and the SNR limits created by the

weaker signal and higher gains are present simultaneously.

Furthermore, not only does the blocker scenario degrade the

dynamic range, it also reduces the range of input signals that

can be handled because a larger part of the gain range is used

to extract the weak desired signal from the stronger blocker.

KEY PARAMETERS FOR QUADRATURE-BASED

RECEIVERS

The majority of digital communication receivers use quadrature

signaling, in which bits of information are encoded onto pairs of

baseband signals that then modulate in-phase (I) and quadrature

(Q) sinusoidal carriers. Both the baseband and modulated signals

appear quite complex in the time domain with dramatic peaks

and valleys. In a typical receiver, the goal is to recover the pair

of quadrature baseband signals in the presence of noise and

interfering signals after quadrature demodulation. In the process

of filtering out of band noise and unwanted interferers and

restoring the levels of the wanted I and Q baseband signals, it

is critical to retain their gain and phase integrity over the

bandwidth.

In filter mode, the ADRF6520 delivers flat, in band gain and

group delay, consistent with a four-pole Butterworth prototype

filter, as described in the Programmable Filters section.

Furthermore, careful design ensures excellent matching of these

parameters between the I and Q channels. Although absolute

gain flatness and group delay can be corrected with digital

equalization, mismatch introduces quadrature errors and

intersymbol interference that degrade bit error rates in digital

communication systems.

For signals greater than 720 MHz of bandwidth, the filters can

be bypassed, and the ADRF6520 then becomes a dual cascaded

chain of two VGAs, offering a large gain range while maintaining

gain and group delay match between the two channels.

ADRF6520ACPZ-R7 数据表(PDF) 23 Page - Analog Devices

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