Linear Technology LTC2367-18 with LTC6655-5/LT6202: 18-Bit, 500ksps, Pseudo-Differential Unipolar SAR ADC with 97dB SNR. Req DC718 or DC59 DC1813A-G 데이터 시트
제품 코드
DC1813A-G
LT6202/LT6203/LT6204
20
620234fd
TYPICAL APPLICATIONS
Low Noise, Low Power 1MΩ AC
Photodiode Transimpedance Amplifier
Figure 3 shows the LT6202 applied as a transimpedance
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
I
DRAIN
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 I
DSS
of 10mA and a pinchoff voltage between
–0.3V and –1.2V. The JFET gate and the LT6202 output
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 g
m
, 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
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 2mV
P-P
over a 20MHz bandwidth.
–
+
V
BIAS
–
PHILIPS
BF862
R1
499k
R2
499k
C1
1pF
V
S
–
V
S
+
V
OUT
V
S
= ±5V
LT6202
R3
4.99k
LT6202/03/04 F03
Figure 3. Low Noise, Low Power 1MΩ
AC Photodiode Transimpedance Amplifier
–
+
V
BIAS
–
PHILIPS
BF862
R1
499k
R2
499k
C1
1pF
V
S
–
V
S
+
V
OUT
V
S
= ±5V
R3
4.99k
C2
0.1µF
LTC2050HV
R4
10M
R5
10k
C3
1µF
LT6202/03/04 F04
–
+
LT6202
Figure 4. Precision Low Noise, Low Power Transimpedance Amplifier