AD8364ACPZ-R2 Analog Devices, AD8364ACPZ-R2 Datasheet - Page 22

• Manufacturer Part Number: AD8364ACPZ-R2
• Description: LF to 2.7GHz, Dual 60dB TruPwr Detector
• Manufacturer: Analog Devices

AD8364
MEASUREMENT CHANNEL DIFFERENCE OUTPUT
USING OUT[P, N]
The AD8364 incorporates two operational amplifiers with rail-
to-rail output capability to provide a channel difference output.
As in the case of the output drivers for OUT[A, B], the output
stages have the capability of driving 70 mA. The output noise is
approximately 40 nV/√Hz at 100 kHz. OUTA and OUTB are
internally connected through 1 kΩ resistors to the inputs of each
op amp. The pin VLVL is connected to the positive terminal of
both op amps through 1 kΩ resistors to provide level shifting. The
negative feedback terminal is also made available through a 1 kΩ
resistor. The input impedance of VLVL is 1 kΩ and FBK[A, B]
is 2 kΩ. See Figure 59 for the connections of these pins.
If OUTP is connected to FBKA, then OUTP is given as
If OUTN is connected to FBKB, then OUTN is given as
In this configuration, all four measurements, OUT[A, B, P, N],
are made available simultaneously. A differential output can be
taken from OUTP − OUTN, and VLVL can be used to adjust
the common-mode level for an ADC connection.
PWDN
COMR
VPSA
VPSB
INHA
INHB
INLA
INLB
OUTP = OUTA – OUTB + VLVL
OUTN = OUTB – OUTA + VLVL
25
26
27
28
29
30
31
32
Figure 59. Op Amp Connections (All Resistors are 1 kΩ ± 20%)
24
CHANNEL A
CHANNEL B
1
TEMP
TruPwr™
TruPwr™
23
2
OUTB
OUTA
BIAS
22
3
I
I
I
I
VGA
CONTROL
TGT
TGT
SIG
SIG
21
4
VGA
CONTROL
2
2
2
2
20
5
19
6
18
7
17
8
16
15
14
13
12
11
10
9
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
(9)
(10)
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CONTROLLER MODE
The channel difference outputs can be used for controlling a
feedback loop to the AD8364’s RF inputs. A capacitor connected
between FBKA and OUTP forms an integrator, keeping in mind
that the on-chip 1 kΩ feedback resistor forms a zero. (The value
of the on-chip resistors can vary as much as ±20% with manufac-
turing process variation.) If Channel A is driven and Channel B
has a feedback loop from OUTP through a PA, then OUTP
integrates to a voltage value such that
The output value from OUTN may or may not be useful. It is
given by
For VLVL < OUTA/3,
Otherwise,
If VLVL is connected to OUTA, then OUTB is forced to equal
OUTA through the feedback loop. This flexibility provides the
user with the capability to measure one channel operating at a
given power level and frequency while forcing the other channel
to a desired power level at another frequency. ADJA and ADJB
should be set to different voltage levels to reduce the temperature
drift of the output measurement. The temperature drift will be
statistical sum of the drift from Channel A and Channel B. As
stated before, VLVL can be used to force the slaved channel to
operate at a different power than the other channel. If the two
channels are forced to operate at different power levels, then
some static offset occurs due to voltage drops across metal
wiring in the IC.
If an inversion is necessary in the feedback loop, OUTN can be
used as the integrator by placing a capacitor between OUTN
and OUTP. This changes the output equation for OUTB and
OUTP to
For VLVL < OUTA/2,
Otherwise,
The previous equations are valid when Channel A is driven and
Channel B is slaved through a feedback loop. When Channel B
is driven and Channel A is slaved, the above equations can be
altered by changing OUTB to OUTA and OUTN to OUTP.
OUTB = (OUTA + VLVL)/2
OUTN = 0 V
OUTN = (3 × VLVL – OUTA)/2
OUTB = 2 × OUTA − VLVL
OUTN = 0 V
OUTN = 2 × VLVL – OUTA
(11)
(12)
(13)
(14)
(15)
(16)