ADRF6510ACPZ-WP Analog Devices Inc, ADRF6510ACPZ-WP Datasheet - Page 17

• Manufacturer Part Number: ADRF6510ACPZ-WP
• Manufacturer: Analog Devices Inc

Specifications of ADRF6510ACPZ-WP

• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 32
• Lead Free Status / RoHS Status: Supplier Unconfirmed

Note that the noise spectral density outside the filter bandwidth
is limited by the fixed VGA output noise. It may be necessary to
use an external, fixed-frequency, passive filter prior to an analog-
to-digital conversion to prevent noise aliasing from degrading
the signal-to-noise ratio. The higher the sampling rate relative
to the maximum ADRF6510 corner frequency setting to be used,
the lower the order of the external filter.
DISTORTION CHARACTERISTICS
The distortion performance of the ADRF6510 is similar to its
noise performance. The filters and the VGAs contribute to the
overall distortion and signal handling capabilities. Furthermore,
the front end must also cope with out-of-band signals that can be
larger than the in-band signals. These out-of-band signals are
filtered before reaching the VGA. It is important to understand
the signals presented to the ADRF6510 and to match these
signals with the input and output characteristics of the part.
When the gain is low, the distortion is typically limited by the
input section because the output is not driven to its maximum
capacity. When the gain is high, the distortion is likely limited
by the output section because the input is not driven to its
maximum capacity. An exception to this is when the input is
driven with a small desired signal in combination with a large
out-of-band signal. In this case, the out-of-band signal may
drive the input to distort. As long as the input is not overdriven,
the out-of-band signal is removed by the filter. A high VGA
gain is still needed to raise the small desired signal to a higher
level at the output. The overall distortion introduced by the part
depends on the input drive level, including the out-of-band
signals, and the desired output signal level.
As noted in the Input Buffers section, the input section can
handle a total signal level of 1 V p-p for a 6 dB preamplifier and
500 mV p-p for a 12 dB preamplifier with >50 dBc harmonic
distortion. This includes both in-band and out-of-band signals.
–100
–105
–110
–115
–120
–125
–130
–135
Figure 47. Total Output Noise with a 1 MHz Corner Frequency
0.5
1.0
for Three Different Gain Settings
GAIN = 0dB
GAIN = 20dB
FREQUENCY (MHz)
1.5
GAIN = 40dB
2.0
BANDWIDTH = 1MHz
2.5
3.0
Rev. 0 | Page 17 of 28
To distinguish and quantify the distortion performance of the
input section, two different IP3 specifications are presented.
The first is called in-band IP3 and refers to a two-tone test
where the signals are inside the filter bandwidth. This is exactly
the same figure of merit familiar to communications engineers
in which the third-order intermodulation level, IM3, is
measured.
To quantify the effect of out-of-band signals, a new out-of-band
(OOB) IIP3 figure of merit is introduced. This test also involves
a two-tone stimulus; however, the two tones are placed out-of-
band so that the lower IM3 product lands in the middle of the
filter pass band. At the output, only the IM3 product is visible
because the original two tones are filtered out. To calculate the
OOB IP3 at the input, the IM3 level is referred to the input by
the overall gain. The OOB IIP3 allows the user to predict the
impact of out-of-band blockers or interferers at an arbitrary
signal level on the in-band performance. The ratio of the
desired input signal level to the input-referred IM3 at a given
blocker level represents a signal-to-distortion limit imposed by
the out-of-band signals.
MAXIMIZING THE DYNAMIC RANGE
The role of the ADRF6510 is to increase the level of a variable
in-band signal while minimizing out-of-band signals. Ideally,
this is achieved without degrading the SNR of the incoming
signal or introducing distortion to the incoming signal.
The first goal is to maximize the output signal swing, which can
be defined by the ADC input range or the input signal capacity
of the next analog stage. For the complex waveforms often encoun-
tered in communication systems, the peak-to-average ratio, or
crest factor, must be considered when choosing the peak-to-peak
output. From the chosen output signal and the maximum gain
of the ADRF6510, the minimum input level can be defined.
Lower signal levels do not yield the maximum output and suffer
a greater degradation in SNR.
As the input signal level increases, the VGA gain is reduced from
its maximum gain point to maintain the desired fixed output
level. The output noise, initially dominated by the filter, follows
the gain reduction, yielding a progressively better SNR. At some
point, the VGA gain drops sufficiently that the constant VGA
noise becomes dominant, resulting in a constant SNR from that
point. From the perspective of SNR alone, the maximum input
level is reached when the VGA reaches its minimum gain.
Distortion must also be considered when maximizing the dynamic
range. At low and moderate signal levels, the output distortion
is constant and assumed to be adequate for the selected output
level. At some point, the input signal becomes large enough that
distortion at the input limits the system. The maximum tolerable
input signal depends on whether the input distortion becomes
unacceptably large or the minimum gain is reached.
ADRF6510