adl5504 Analog Devices, Inc., adl5504 Datasheet - Page 18

• Manufacturer Part Number: adl5504
• Description: 450 Mhz To 6000 Mhz Trupwr Detector
• Manufacturer: Analog Devices, Inc.

ADL5504
Figure 44 shows a plot of the error at 25°C, the temperature
at which the ADL5504 is calibrated. Note that the error is not 0;
this is because the ADL5504 does not perfectly follow the ideal
linear equation, even within its operating region. The error at
the calibration points is, however, equal to 0 by definition.
Figure 44 also shows error plots for the output voltage at −40°C
and +85°C. These error plots are calculated using the gain and
intercept at 25°C. This is consistent with calibration in a mass
production environment where calibration at temperature is not
practical.
CALIBRATION FOR IMPROVED ACCURACY
Another way of presenting the error function of the ADL5504
is shown in Figure 45. In this case, the decibel (dB) error at hot
and cold temperatures is calculated with respect to the transfer
function at ambient temperature. This is a key difference in
comparison to Figure 44, in which the error was calculated
with respect to the ideal linear transfer function at ambient
temperature. When this alternative technique is used, the
error at ambient temperature becomes equal to 0 by definition
(see Figure 45).
+85°C vs. +25°C Linear Reference, 1900 MHz Frequency, 3.0 V Supply
Figure 44. Error from Linear Reference vs. Input at −40°C, +25°C, and
–1
–2
–3
3
2
1
0
–25
–20
–15
+85°C
–10
INPUT (dBm)
–5
+25°C
–40°C
0
5
10
15
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This plot is a useful tool for estimating temperature drift at a
particular power level with respect to the (nonideal) response
at ambient temperature. The linearity and dynamic range tend
to be improved artificially with this type of plot because the
ADL5504 does not perfectly follow the ideal linear equation
(especially outside of its linear operating range). Achieving
this level of accuracy in an end application requires calibration
at multiple points in the operating range of the device.
In some applications, very high accuracy is required at just one
power level or over a reduced input range. For example, in a
wireless transmitter, the accuracy of the high power amplifier
(HPA) is most critical at or close to full power. The ADL5504
offers a tight error distribution in the high input power range,
as shown in Figure 45. The high accuracy range, beginning
around 2 dBm at 1900 MHz, offers 12 dB of ±0.15 dB detection
error over temperature. Multiple point calibration at ambient
temperature in the reduced range offers precise power
measurement with near 0 dB error from −40°C to +85°C.
Figure 45. Error from +25°C Output Voltage at −40°C, +25°C, and +85°C After
Note that the high accuracy range center varies over frequency
(see Figure 13 to Figure 15 and Figure 19 to Figure 21).
–1
–2
–3
Ambient Normalization, 1900 MHz Frequency, 3.0 V Supply
3
2
1
0
–25
+25°C
–20
–15
–10
INPUT (dBm)
+85°C
–40°C
–5
0
5
10
15