AD8364ACPZ-R2 Analog Devices, AD8364ACPZ-R2 Datasheet - Page 31

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

TEMPERATURE COMPENSATION ADJUSTMENT
The AD8364 has a highly stable measurement output with
respect to temperature. However, when the RF inputs exceed a
frequency of 600 MHz, the output temperature drift must be
compensated for using ADJ[A, B] for optimal performance.
Proprietary techniques are used to compensate for the temper-
ature drift. The absolute value of compensation varies with
frequency, balun choice, and circuit board material. Table 5
shows recommended voltages for ADJ[A, B] to maintain a
temperature drift error of typically ±0.5 dB or better over the
entire rated temperature range with the recommended baluns.
Table 5. Recommended Voltages for ADJ[A, B]
Frequency (MHz)
ADJ[A, B] (V)
Compensating the device for temperature drift using ADJ[A, B]
allows for great flexibility. If the user requires minimum temper-
ature drift at a given input power or subset of the dynamic range,
the ADJ[A, B] voltage can be swept while monitoring OUT[A, B]
over temperature. Figure 67 shows the result of such an exercise
with a broadband balun, one that is not the recommended balun
at 1880 MHz. The value of ADJ[A, B] where the output has
minimum movement (approximately 0.77 V for the example in
Figure 67) is the recommended voltage for ADJ[A, B] to achieve
minimum temperature drift at a given power and frequency.
The ADJ[A, B] input has high input impedance. The input can
be conveniently driven from an attenuated value of VREF using
a resistor divider, if desired.
1.70
1.65
1.60
1.55
1.50
1.45
1.40
Figure 67. OUTA vs. ADJA over Temp. Pin = −30 dBm, 1.9 GHz
0
0.25
0.50
450
0
0.75
1.00
880
0.5
ADJA (V)
1.25
1.50
1880
0.65
1.75
+85°C
+65°C
+45°C
+25°C
+10°C
–20°C
–40°C
2.00
2140
0.85
2.25
2.50
2500
1.10
Rev. 0 | Page 31 of 48
Figure 68 shows a simplified schematic representation of the
ADJ[A, B] interface.
DEVICE CALIBRATION AND ERROR CALCULATION
The measured transfer function of the AD8364 at 2.14 GHz is
shown in Figure 69. The figure shows plots of both output
voltage vs. input power and calculated error vs. input power. As
the input power varies from −50 dBm to 0 dBm, the output
voltage varies from 0.4 V to about 2.8 V.
V
V
Because slope and intercept vary from device to device, board-
level calibration must be performed to achieve high accuracy.
The equation for output voltage can be written as
Where Slope is the change in output voltage divided by the
change in power (dB), and Intercept is the calculated power at
which the output voltage would be 0 V. (Note that Intercept is a
theoretical value; the output voltage can never achieve 0 V).
In general, the calibration is performed by applying two known
signal levels to the AD8364’s input and measuring the
corresponding output voltages. The calibration points are
generally chosen to be within the linear-in-dB operating range
of the device (see the Specifications section for more details).
OUT
OUT
2
1
V
3.50
3.15
2.80
2.45
2.10
1.75
1.40
1.05
0.70
0.35
OUT
INTERCEPT
0
–60
= Slope × (P
Figure 68. ADJ[A, B] Interface Simplified Schematic
–55 –50
ADJ[A, B]
Figure 69. Transfer Function at 2.14 GHz.
P
–45 –40 –35
ERROR CW –40°C
IN
1
IN
ERROR CW +25°C
− Intercept)
COMR IADJ[A, B]
–30
VPSR
P
–25 –20 –15
IN
2
INTERNAL
CURRENT
BLUE = –40°C
GREEN = +25°C
RED = +85°C
P
IN
MEAS (dBm)
ERROR CW +85°C
VREF/2
–10
–5
0
AD8364
5
10
2.0
1.6
1.2
0.8
0.4
0
–0.4
–0.8
–1.2
–1.6
–2.0