Datasheet LT1169 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Dual Low Noise, Picoampere Bias Current, JFET Input Op Amp |
| Pages / Page | 12 / 10 — APPLICATI. S I FOR ATIO. High Speed Operation. Figure 5. Three Op Amp … |
| File Format / Size | PDF / 302 Kb |
| Document Language | English |
APPLICATI. S I FOR ATIO. High Speed Operation. Figure 5. Three Op Amp Instrumentation Amplifier. Figure 6. TYPICAL APPLICATIONS N
Model Line for this Datasheet
Text Version of Document
LT1169
O U U W U APPLICATI S I FOR ATIO
15V Input offset current = 3pA 3 8 R4 R6 IN– + Input resistance = 1013 1/2 1k 10k Ω 1 LT1169 2 IC1 Input noise = 3.4µVP-P – C1 R1 4 30pF 1k –15V
High Speed Operation
R2 2 – The low noise performance of the LT1169 was achieved by 200Ω 1/2 1 enlarging the input JFET differential pair to maximize the LT1169 OUTPUT 6 – R3 3 + IC2 first stage gain. Enlarging the JFET geometry also increases R5 1k CL 1/2 7 1k the parasitic gate capacitance, which if left unchecked, can LT1169 5 + IC1 result in increased overshoot and ringing. When the feed- R7 IN+ 10k back around the op amp is resistive (RF), a pole will be GAIN = 100 created with R BANDWIDTH = 330kHz F, the source resistance and capacitance INPUT REFERRED NOISE = 8.7nV/√ Hz AT 1kHz (RS,CS), and the amplifier input capacitance (CIN = 1.5pF). WIDEBAND NOISE DC TO 330kHz = 5.3µVRMS C 0.01µF LT1169 • F05 L ≤ In closed-loop gain configurations with RS and RF in the M
Figure 5. Three Op Amp Instrumentation Amplifier
Ω range (Figure 6), this pole can create excess phase shift and even oscillation. A small capacitor (CF) in parallel with Assume CMRRA = 50µV/V or 86dB, RF eliminates this problem. With RS(CS + CIN) = RFCF, the and CMRR effect of the feedback pole is completely removed. B = 39µV/V or 88dB, then ∆CMRR = 11µV/V or 99dB; CF if CMRRB = –39µV/V which is still 88dB, then ∆CMRR = 89µV/V or 81dB RF By specifying and guaranteeing all of these matching – parameters, the LT1169 can significantly improve the C OUTPUT IN performance of matching-dependent circuits. RS CS + Typical performance of the instrumentation amplifier: LT1169 • F06
Figure 6
Input offset voltage = 0.8mV Input bias current = 4pA
U TYPICAL APPLICATIONS N Unity-Gain Buffer with Extended Load Capacitance Drive Capability Light Balance Detection Circuit
R2 R1 1k 1M C1 I1 C1 3pF TO 5pF – PD1 R1 33Ω – 1/2 LT1169 V I OUT 2 + V C 1/2 LT1169 V IN L OUT PD2 + LT1169 • TA03 C1 = CL ≤ 0.1µF LT1169 • TA04 OUTPUT SHORT CIRCUIT CURRENT (∼ 30mA) WILL LIMIT THE RATE VOUT = 1M × (I1 – I2) AT WHICH THE VOLTAGE CAN CHANGE ACROSS LARGE CAPACITORS PD1,PD2 = HAMAMATSU S1336-5BK dV (I = C ) WHEN EQUAL LIGHT ENTERS PHOTODIODES, V dt OUT < 3mV. 10
O U U W U APPLICATI S I FOR ATIO
15V Input offset current = 3pA 3 8 R4 R6 IN– + Input resistance = 1013 1/2 1k 10k Ω 1 LT1169 2 IC1 Input noise = 3.4µVP-P – C1 R1 4 30pF 1k –15V
High Speed Operation
R2 2 – The low noise performance of the LT1169 was achieved by 200Ω 1/2 1 enlarging the input JFET differential pair to maximize the LT1169 OUTPUT 6 – R3 3 + IC2 first stage gain. Enlarging the JFET geometry also increases R5 1k CL 1/2 7 1k the parasitic gate capacitance, which if left unchecked, can LT1169 5 + IC1 result in increased overshoot and ringing. When the feed- R7 IN+ 10k back around the op amp is resistive (RF), a pole will be GAIN = 100 created with R BANDWIDTH = 330kHz F, the source resistance and capacitance INPUT REFERRED NOISE = 8.7nV/√ Hz AT 1kHz (RS,CS), and the amplifier input capacitance (CIN = 1.5pF). WIDEBAND NOISE DC TO 330kHz = 5.3µVRMS C 0.01µF LT1169 • F05 L ≤ In closed-loop gain configurations with RS and RF in the M
Figure 5. Three Op Amp Instrumentation Amplifier
Ω range (Figure 6), this pole can create excess phase shift and even oscillation. A small capacitor (CF) in parallel with Assume CMRRA = 50µV/V or 86dB, RF eliminates this problem. With RS(CS + CIN) = RFCF, the and CMRR effect of the feedback pole is completely removed. B = 39µV/V or 88dB, then ∆CMRR = 11µV/V or 99dB; CF if CMRRB = –39µV/V which is still 88dB, then ∆CMRR = 89µV/V or 81dB RF By specifying and guaranteeing all of these matching – parameters, the LT1169 can significantly improve the C OUTPUT IN performance of matching-dependent circuits. RS CS + Typical performance of the instrumentation amplifier: LT1169 • F06
Figure 6
Input offset voltage = 0.8mV Input bias current = 4pA
U TYPICAL APPLICATIONS N Unity-Gain Buffer with Extended Load Capacitance Drive Capability Light Balance Detection Circuit
R2 R1 1k 1M C1 I1 C1 3pF TO 5pF – PD1 R1 33Ω – 1/2 LT1169 V I OUT 2 + V C 1/2 LT1169 V IN L OUT PD2 + LT1169 • TA03 C1 = CL ≤ 0.1µF LT1169 • TA04 OUTPUT SHORT CIRCUIT CURRENT (∼ 30mA) WILL LIMIT THE RATE VOUT = 1M × (I1 – I2) AT WHICH THE VOLTAGE CAN CHANGE ACROSS LARGE CAPACITORS PD1,PD2 = HAMAMATSU S1336-5BK dV (I = C ) WHEN EQUAL LIGHT ENTERS PHOTODIODES, V dt OUT < 3mV. 10
