Datasheet LT1169 (Analog Devices) - 9

LT1169
O U U W U APPLICATI S I FOR ATIO
R R2 F CB CF R – B – C OUTPUT R1 S RS OUTPUT + + C  B = CF CS TRANSDUCER R  B = RF RS CS RS C ≅ B CS dQ dV Q = CV; = I = C R R B = RS C  dt  dt B B RS > R1 OR R2 TRANSDUCER LT1169 • F03
Figure 3. Inverting and Noninverting Gain Configurations Input:
±
5.2 Sine Wave LT1169 Output OPA2111 Output
LT1169 • F04a LT1169 • F04b LT1169 • F04c
Figure 4. Voltage Follower with Input Exceeding the Common Mode Range (VS =
±
5V)
capacitor CB, is used to cancel the phase shift caused by amps. Two or three op amp instrumentation amplifiers, the op amp input capacitance and RB. tracking voltage references and low drift active filters are some of the circuits requiring matching between two
Reduced Power Supply Operation
op amps. To take full advantage of a wide input common-mode The well-known triple op amp configuration in Figure 5 range, the LT1169 was designed to eliminate phase rever- illustrates these concepts. Output offset is a function of the sal. Referring to the photographs in Figure 4, the LT1169 difference between the two halves of the LT1169. This error is shown operating in the follower mode (AV = 1) at ±5V cancellation principle holds for a considerable supplies with the input swinging ±5.2V. The output of the number of input referred parameters in addition to LT1169 clips cleanly and recovers with no phase reversal, offset voltage and bias current. Input bias current will unlike the competition as shown by the last photograph. be the average of the two noninverting input currents (I + B ). This has the benefit of preventing lockup in servo systems The difference between these two currents (∆I + B ) and minimizing distortion components. The effect of input is the offset current of the instrumentation amplifier. Com- and output overdrive on one amplifier has no effect on the mon-mode and power supply rejections will be other, as each amplifier is biased independently. dependent only on the match between the two amplifiers
Advantages of Matched Dual Op Amps
(assuming perfect resistor matching). In many applications the performance of a system The concepts of common mode and power supply depends on the matching between two operational ampli- rejection ratio match (∆CMRR and ∆PSRR) are best dem- fiers rather than the individual characteristics of the two op onstrated with a numerical example: 9