AD8364-EVAL Analog Devices, AD8364-EVAL Datasheet - Page 18

• Manufacturer Part Number: AD8364-EVAL
• Description: LF to 2.7GHz, Dual 60dB TruPwr Detector
• Manufacturer: Analog Devices

PRELIMINARY TECHNICAL DATA
OUT[A,B,P,N] Outputs
The output drivers used in the AD8364 are different than the
output stage on the AD8362. The AD8364 incorporates rail-to-
rail output drivers with pull-up and pull-down capability.
OUT[A,B,P,N] can source and sink up 70mA. There is also an
internal load from both OUTA and OUTB to ACOM of 2.5KΩ.
Measurement Difference Output using OUT[P,N]
The AD8364 incorporates two operational amplifiers with rail-
to-rail output capability to provide a difference output. As in the
case of the output drivers for OUT[A,B], the output stages have
the capability of driving 160mA. OUTA and OUTB are
internally connected through 1KΩ resistors to the inputs of each
op-amp. The pin VLVL is connected to the positive terminal of
both op-amps through 1KΩ resistors to provide level shifting.
The negative feedback terminal is also made available through a
1KΩ resistor. The input impedance of VLVL is 1KΩ and
FBK[A,B] is 2KΩ.. See figure 32 below for the connections of
these pins.
If OUTP is connected to FBKA, then OUTP will be given as:
If OUTN is connected to FBKB, then OUTN will be given as:
In this configuration, all four measurements are made available
simultaneously OUT[A,B,P,N]. A differential output can be
taken from OUTP – OUTN and VLVL can be used to adjust the
common mode level for an ADC connection.
Controller mode
The difference outputs can be used for controlling a feedback
loop to the AD8364’s RF inputs. A capacitor connected between
FBKA and OUTP will form an integrator, keeping in mind that
the 1KΩ feedback resistor forms a zero. The sheet resistance of
the on chip resistors is ±12%. If Channel A is driven and
Channel B has a feedback loop from OUTP through a PA, then
OUTP will integrate to a voltage value such that:
Figure 32. Op-Amp Connections (All resistors are 1KΩ±12%)
PWDN
VPSA
COMR
VPSB
INHA
INHB
INL A
INLB
OUTN = OUTB – OUTA + VLVL
2
2
3
2
2
3
3
OUTP = OUTA – OUTB + VLVL
25
7
8
6
9
0
1
2
CHPB
CHPA
24
1
TruPwr™
TruPwr™
DECB
Channel B
DECA
Channel A
23
2
COMB ADJB ADJA VREF VLVL CLPB
COMA VPSR ACMB TEMP ACMA CLPA
22
3
OUTA
OUTB
BIAS
21
4
20
5
V2I
TEMP
19
6
18
7
V2I
17
8
16
15
14
13
12
11
10
9
(10)
(9)
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
Rev. PrC Ι Page 18 of 23
The output value from OUTN may or may not be useful. It
is given by:
For VLVL < OUTA/3,
Else,
If VLVL is connected to OUTA, then OUTB will be forced
to equal OUTA through the feedback loop. This flexibility
provides the user with the capability to measure one channel
operating at given power level and frequency while forcing
the other channel to the same power level, or another desired
power level, at another frequency. If both channels are
operating at the same frequency and ADJA = ADJB, then
there will be little to no temperature drift. When different
frequencies are driven into each channel, ADJA and ADJB
must be set accordingly to reduce the temperature drift of
the output measurement. The temperature drift will be a
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 level, then some static offset will occur due
to voltage drops across metal wiring internal to 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,
Else,
The above equations are valid when Channel A is driven and
Channel B is slaved through a feedback loop. When Channel
B is driven and Channel B is slaved, the above equations can
be altered by changing OUTB to OUTA and OUTN to
OUTP.
Temperature Compensation Adjustment
The AD8364 has a highly stable measurement output with
respect to temperature. However, when the RF inputs exceed
a frequency of 1.7GHz, the output temperature drift must be
compensated using ADJ[A/B]. Proprietary techniques are
used to compensate for the temperature drift. However, the
OUTN = (3*VLVL – OUTA)/2
OUTB = (OUTA + VLVL)/2
OUTN = 2*VLVL – OUTA
OUTB = 2*OUTA – VLVL
OUTN = 0V (12)
OUTN = 0V
(15)
AD8364
(14)
(16)
(11)
(13)