ADL5519-EVALZ Analog Devices Inc, ADL5519-EVALZ Datasheet - Page 30

• Manufacturer Part Number: ADL5519-EVALZ
• Description: EVALUATION BOARD FOR ADL5519
• Manufacturer: Analog Devices Inc
• Series: -r
• Type: Controllerr

Specifications of ADL5519-EVALZ

• Frequency: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: *
• Other names: Q4463053

ADL5519
AUTOMATIC GAIN CONTROL
Figure 67 shows how the ADL5519 can be connected to provide
automatic gain control to an amplifier or signal chain. Additional
pins are omitted for clarity. In this configuration, both detectors
are connected in measurement mode with appropriate filtering
being used on CLPA, CLPB to provide adequate filtering of the
demodulated log output. OUTA, however, is also connected to
the VLVL pin of the on-board difference amplifier. In addition,
the OUTP output of the difference amplifier drives a variable gain
element (either VVA or VGA) and is connected back to the FBKA
input via a capacitor so that it is operating as an integrator.
Assume that OUTA is much bigger than OUTB. Because OUTA
also drives VLVL, this voltage is also present on the noninverting
input of the op amp driving OUTP. This results in a current flow
from OUTP through the integrating capacitor into the FBKA input.
This results in the voltage on OUTP increasing. If the gain control
transfer function of the VGA/VVA is positive, this increases the
gain, which in turn increases the input signal to INHA. The
output voltage on the integrator continues to increase until the
power on the two input channels is equal, resulting in a signal
chain gain of unity.
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If a gain other than 0 dB is required, an attenuator can be used
in one of the RF paths, as shown in Figure 67. Alternatively,
power splitters or directional couplers of different coupling
factors can be used. Another convenient option is to apply a
voltage on VLVL other than OUTA. Refer to Equation 18 and
the Controller Mode section for more detail.
If the VGA/VVA has a negative gain control sense, the OUTN
output of the difference amplifier can be used with the integrating
capacitor tied back to FBKB. Alternatively, the inputs could be
swapped.
The choice of the integrating capacitor affects the response time
of the AGC loop. Small values give a faster response time but
may result in instability, whereas larger values reduce the response
time. Capacitors that are too large can also cause oscillations due
to the capacitive drive capability of the op amp. In automatic gain
control, the capacitors on CLPA and CLPB, which perform the
filtering of the demodulated log output, must still be used and
also affect loop response time.