Datasheet

LTC6360
21
6360f
applicaTions inForMaTion
Low Noise, True Zero 1MΩ Photodiode
Transimpedance Amplifier
Figure 13 shows the LTC6360 applied as a transimped-
ance amplifier. The LTC6360 charge pump drives the
anode of the photodiode. The BF862 ultra low noise JFET
(J1) acts as a source follower, buffering the input of the
LTC6360 and making it suitable for the high impedance
feedback element R1. The BF862 has a minimum I
DSS
of
10mA and a pinchoff voltage between –0.3V and –1.2V.
The LTC2054 chopper stabilized op amp acts to servo
the DC voltage at the JFET gate to 0V, which allows the
output of the LTC6360 to swing to 0V when there is no
photo diode current.
Amplifier output noise density is dominated by the
130nV/√Hz of the feedback resistor at low frequency, rising
to 320nV/√Hz at 1MHz. Note that because the JFET has a
g
m
of approximately 1/100Ω, its attenuation looking into
R2 is only about 10%. The closed loop bandwidth using
a SFH213 photodiode was measured at approximately
3.2MHz.