adl5336 Analog Devices, Inc., adl5336 Datasheet - Page 21

• Manufacturer Part Number: adl5336
• Description: Cascadable If Vgas With Programmable Rms Detectors
• Manufacturer: Analog Devices, Inc.

DETECTOR OUTPUT AND GAIN PIN
The
cell has a VGA output applied to its input. This is shown Figure 1
and Figure 62. These on-board detector squaring cells are used to
achieve an AGC function with the VGAs. Each of the squared
output signals is compared to a reference signal and the difference
is then output in a current-mode signal. The DTO1 pin is the
detector squaring cell output that taps off of the output VGA1,
and the DTO2 pin is the detector squaring cell output that taps
off of the output of VGA2. By shorting the DTO1 and GAIN1
pins together and putting a capacitor to ground on the DTO1/
GAIN1 node, the AGC function can be achieved using VGA1.
The same connections can be done to DTO2 and GAIN2 to
achieve the AGC function using VGA2. The MODE pin must
be pulled low for the AGC function. For more information on
the detector squaring cells and the AGC function, refer to the
AGC Operation section. For information concerning the capacitor
value used, refer to the Theory of Operation section.
COMMON-MODE BYPASSING
Decouple the two common-mode pins, VCM1 (Pin 1) and VCM2
(Pin 24), of the
ceramic capacitors. The evaluation board has 0.1 μF capacitor
values for each of the common-mode pins (see Figure 70).
SERIAL PORT CONNECTIONS
The SPI port of the
reads data out of it. The SPI port controls maximum VGA gain
levels, output setpoint levels, and VGA2 input selection. It is
recommended to put low-pass RC filtering on the SPI lines to
filter out any high frequency glitches if reading and writing to the
SPI port becomes problematic. Capacitors C26 through C29,
shown in Figure 70, can be populated, along with replacing the
standard 0 Ω jumper resistors (R9 to R12) to make an
appropriate low-pass RC filter network on each SPI line.
ADL5336
has a pair of detector squaring cells. Each squaring
ADL5336
ADL5336
using low inductance, surface-mount
writes data into the device and
Rev. A | Page 21 of 32
MODE AND ENABLE CONNECTIONS
The
This function is controlled by the MODE pin. When the MODE
is pulled high, it puts each VGA into traditional VGA mode, where
the gain slope is positive. When the MODE pin is pulled to
ground, both VGAs have a negative gain slope, which is needed
to obtain an AGC function with either VGA. The MODE
threshold voltage levels are: V
slope and V
Pulling the ENBL pin high enables the part and allows for normal
operation. If the ENBL pin is pulled low, then the
down and only draws approximately 4 mA of supply current.
ERROR VECTOR MAGNITUDE (EVM)
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, as signal power increases, the distortion components
increase. A typical receiver exhibits the three following distinct
EVM limitations vs. the received input signal power:
•
•
•
ADL5336
At large enough signal levels, where the distortion
components 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 optimal level
determined dominantly by either the quadrature accuracy
and I/Q gain match of the signal chain or the precision of
the test equipment.
As signal levels decrease, such that noise is a major
contributor, 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.
MODE
can have both a positive and negative gain slope.
< 2 V for the negative gain slope.
MODE
> 3 V for the positive gain
ADL5336
ADL5336
powers