AD8305ACP-REEL7 Analog Devices Inc, AD8305ACP-REEL7 Datasheet - Page 15

• Manufacturer Part Number: AD8305ACP-REEL7
• Description: IC,Converter, Other/Special/Miscellaneous,LLCC,16PIN
• Manufacturer: Analog Devices Inc
• Type: Logarithmic Converterr

Specifications of AD8305ACP-REEL7

• Rohs Status: RoHS non-compliant
• Design Resources: Interfacing ADL5315 to Translinear Logarithmic Amplifier (CN0056) Interfacing ADL5317 High Side Current Mirror to a Translinear Logarithmic Amplifier in an Avalanche Photodiode Power Detector
• Applications: Fiber Optics
• Mounting Type: Surface Mount
• Package / Case: 16-LFCSP

CALIBRATION
The AD8305 has a nominal slope and intercept of 200 mV/decade
and 1 nA, respectively. These values are untrimmed, and the
slope alone may vary as much as 7.5% over temperature. For
this reason, it is recommended that a simple calibration be done
to achieve increased accuracy.
Figure 36. Using Two-Point Calibration to Increase Measurement Accuracy
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
1n
10n
UNCALIBRATED ERROR
100n
IDEAL OUTPUT
MEASURED OUTPUT
1µ
I
PD
(A)
10µ
CALIBRATED ERROR
100µ
1m
10m
–1
–2
–3
4
3
2
1
0
Rev. B | Page 15 of 24
Figure 36 shows the improvement in accuracy when using a two
point calibration method. To perform this calibration, apply
two known currents, I
between 10 nA and 1 mA. Measure the resulting output, V
V
The same calibration is performed with two known optical
powers, P
measurement system while providing a simplified relationship
between the incident optical power and V
The uncalibrated error line in Figure 36 is generated assuming
that the slope of the measured output was 200 mV/ decade
when in fact it was actually 194 mV/decade. Correcting for this
discrepancy decreased measurement error up to 3 dB.
2
, respectively, and calculate the slope m and intercept b.
m = (V
b = V
m = (V
b = V
1
1
1
and P
– m × log
− m × P
1
1
− V
− V
2
2
2
. This allows for calibration of the entire
)/[log
)/(P
1
10
1
1
(I
− P
10
and I
1
(I
)
1
2
) − log
)
2
, in the linear operating range
10
(I
2
)]
LOG
voltage.
AD8305
1
and
(10)
(7)
(8)
(9)