C2719 View Datasheet(PDF) - Hamamatsu Photonics
Part Name
Description
Manufacturer
C2719 Datasheet PDF : 6 Pages
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Photosensor amplifier C2719
Figure 3 Frequency response (S2281 + E2573)
1010
H RANGE
109
108
M RANGE
107
106
L RANGE
105
104
103
100 101 102 103 104 105 106
FREQUENCY (Hz)
KACCB0031EA
Figure 5 Frequency response of output signal and noise (S2281 + E2573)
[Light source: Directly modulated laser diode (DC biased)]
SIGNAL FREQUENCY
RESPONSE
REF -17.0 dBm ATT10 dB
TG LEVEL -10.0 dBm
RBW 100 Hz
VBW 300 Hz
NOISE FREQUENCY
RESPONSE
0
1
2
3
4
5
FREQUENCY (kHz)
KACCB0033EA
Figure 4 Gain peaking
TERMINAL CAPACITANCE:
Ct=12 nF
TERMINAL CAPACITANCE:
Ct=1.2 nF
102
103
104
105
FREQUENCY (Hz)
KACCB0032EA
Figure 6 Schematic pursuit of gain peaking
106
105
104
103
102
101
100
10-1
10-2 f1' f1
f2 f3
10-3
10-1 100 101 102 103 104 105 106 107 108
FREQUENCY (Hz)
KACCB0034EA
I Selecting photodiodes
As described previously, stable measurement may become impossible depending on the photodiode type. The diagrams are
used here to explain how to select a correct photodiode which will not generate gain peaking when used with C2719.
Figure 6 shows an example in which a photodiode with a terminal capacitance Ct of 1.28 nF and a shunt resistance*2 Rsh of 130
MΩ (See note below). In the low-frequency range ➀, the op-amp noise gain of C2719 is determined only by the ratio between Rsh
and the feedback resistance Rf of C2719. Starting from frequency f1 at 1/ωCt > Rsh, the frequency increase is accompanied by
an increase in gain over the interval indicated by ➁. Next, as the frequency increases from f2 at 1/ωCf > Rf, the circuit noise gain
is determined by the ratio of Ct to Cf, during the interval indicated by ➂. Then, in the range covered by interval ➃, the noise gain
decreases, with a slope identical to that of the op-amp open loop gain starting from the point where it contacts frequency f3, which
normally decreases at 6 dB/oct.
At this point, if Ct is multiplied by 10, f1 moves to f1’ and the setting of the noise gain rise at ➁ exceeds the curve of the op-amp
open loop gain. This causes area ➂ to disappear. If this happens, C2719 can no longer maintain stable operation, and gain
peaking appears. Consequently, it is necessary to make sure that area ➂ always exists. With C2719, Rf and Cf are determined
by the sensitivity range. Thus, whether gain peaking occurs or not depends on the Ct value of the photodiode, so selecting the
appropriate photodiode is essential. Figure 7 shows what happens to each of the sensitivity ranges of C2719 when used with
S2281.
10 mV
*2: Shunt resistance Rsh= ID (VR = 10 mV)
3
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