AD8302-EVAL Analog Devices, AD8302-EVAL Datasheet - Page 19

• Manufacturer Part Number: AD8302-EVAL
• Description: LF.2.7 GHz RF/IF Gain and Phase Detector
• Manufacturer: Analog Devices

The comparator mode can be turned into a controller mode by
closing the loop around the V
illustrates a closed loop controller that stabilizes the gain and phase
of a DUT with gain and phase adjustment elements. If V
V
blocks preceding the DUT, the actual gain and phase of the DUT
will be servoed toward the prescribed setpoint gain and phase given
in Equations 11 and 12. These are essentially AGC and APC
loops. Note that as with all control loops of this kind, loop dynam-
ics and appropriate interfaces all must be considered in more detail.
APPLICATIONS
Measuring Amplifier Gain and Compression
The most fundamental application of AD8302 is the monitoring
of the gain and phase response of a functional circuit block such
as an amplifier or a mixer. As illustrated in Figure 12, direc-
tional couplers, DC
signals of the “Black Box” DUT. The attenuators ensure that
the signal levels presented to the AD8302 fall within its dynamic
range. From the discussion in the Dynamic Range section, the
optimal choice places both channels at P
enced to 50 Ω, which corresponds to –43 dBV. To achieve this,
the combination of coupling factor and attenuation are given by,
where C
attenuation factors and GAIN
identical couplers are used for both ports, then the difference in
the two attenuators compensates for the nominal DUT gain. When
the actual gain is nominal, the V
to 0 dB. Variations from nominal gain appear as a deviation from
900 mV or 0 dB with a 30 mV/dB scaling. Depending on the nominal
insertion phase associated with DUT, the phase measurement may
require a fixed phase shift in series with one of the channels to
bring the nominal phase difference presented to the AD8302
near the optimal 90° point.
PHS
C
C
are properly conditioned to drive gain and phase adjustment
B
A
+ L
+ L
B
and C
B
A
MAG
= P
= P
A
IN
IN
are the coupling coefficients, L
– P
+ GAIN
B
and DC
OPT
NOM
MAG
A
MAG
NOM
INPA
INPB
, sample the input and output
–P
AD8302
output is 900 mV, corresponding
and V
OPT
is the nominal DUT gain. If
VMAG
MSET
PSET
VPHS
PHS
OPT
outputs. Figure 11
= –30 dBm refer-
B
and L
MAG
SETPOINT
PHASE
SETPOINT
MAG
A
are the
and
(15)
(16)
When the insertion phase is nominal, the VPHS output is 900 mV.
Deviations from the nominal are reported with a 10 mV/degree
scaling. Table I gives suggested component values for the mea-
surement of an amplifier with a nominal gain of 10 dB and an
input power of –10 dBm.
Table I. Component Values for Measuring a 10 dB Amplifier
with an Input Power of –10 dBm
Component
R1, R2
R5, R6
C1, C4, C5, C6
C2, C8
C3
C7
AttenA
AttenB
DC
The gain measurement application can also monitor gain and
phase distortion in the form of AM-AM (gain compression) and
AM-PM conversion. In this case, the nominal gain and phase
corresponds to those at low input signal levels. As the input level
is increased, output compression and excess phase shifts are
measured as deviations from the low level case. Note that the signal
levels over which the input is swept must remain within the dynamic
range of the AD8302 for proper operation.
A
, DC
“BLACK BOX”
B
DC
DC
A
B
R1
R2
C1
C4
C6
C5
C3
R4
VP
Value
52.3 Ω
100 Ω
0.001 µF
Open
100 pF
0.1 µF
10 dB (See Text)
1 dB (See Text)
20 dB
ATTEN
ATTEN
C7
1
2
3
4
5
6
7
COMM
INPA
OFSA
VPOS
OFSB
INPB
COMM
A
B
AD8302
VMAG
MSET
MFLT
VREF
VPHS
PSET
PFLT
14
13
12
11
10
9
8
AD8302
C2
C8
Quantity
2
2
4
1
1
1
1
2
R5
R6
H
H