LT6202C 查看數據表（PDF） - Linear Technology
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LT6202C Datasheet PDF : 28 Pages
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LT6202/LT6203/LT6204
TYPICAL APPLICATIONS
Low Noise, Low Power 1MΩ AC
Photodiode Transimpedance Amplifier
Figure 3 shows the LT6202 applied as a transimpedance
amplifier (TIA). The LT6202 forces the BF862 ultralow-noise
JFET source to 0V, with R3 ensuring that the JFET has an
IDRAIN of 1mA. The JFET acts as a source follower, buffering
the input of the LT6202 and making it suitable for the high
impedance feedback elements R1 and R2. The BF862 has
a minimum IDSS of 10mA and a pinchoff voltage between
–0.3V and –1.2V. The JFET gate and the LT6202 output
VS+
R1
R2
499k
499k
VBIAS–
PHILIPS
BF862
C1
–
1pF
LT6202
+
VOUT
R3
4.99k
VS–
VS = ±5V
LT6202/03/04 F03
Figure 3. Low Noise, Low Power 1MΩ
AC Photodiode Transimpedance Amplifier
therefore sit at a point slightly higher than one pinchoff
voltage below ground (typically about –0.6V). When the
photodiode is illuminated, the current must come from the
LT6202’s output through R1 and R2, as in a normal TIA.
Amplifier input noise density and gain-bandwidth product
were measured at 2.4nV/Hz and 100MHz, respectively.
Note that because the JFET has a high gm, approximately
1/80Ω, its attenuation looking into R3 is only about 2%.
Gain-bandwidth product was measured at 100MHz and
the closed-loop bandwidth using a 3pF photodiode was
approximately 1.4MHz.
Precision Low Noise, Low Power, 1MΩ
Photodiode Transimpedance Amplifier
Figure 4 shows the LT6202 applied as a transimpedance
amplifier (TIA), very similar to that shown in Figure 3.
In this case, however, the JFET is not allowed to dictate
the DC-bias conditions. Rather than being grounded, the
LT6202’s noninverting input is driven by the LTC2050 to
the exact state necessary for zero JFET gate voltage. The
noise performance is nearly identical to that of the circuit
in Figure 3, with the additional benefit of excellent DC per-
formance. Input offset was measured at under 200µV and
output noise was within 2mVP-P over a 20MHz bandwidth.
VS+
R1
R2
499k
499k
VBIAS–
R4
C2
10M
0.1µF
–
LTC2050HV
+
R5
10k
C3
1µF
PHILIPS
BF862
C1
1pF
–
LT6202
+
R3
4.99k
VOUT
VS–
VS = ±5V
LT6202/03/04 F04
Figure 4. Precision Low Noise, Low Power Transimpedance Amplifier
20
620234fd
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