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LM13700N Arkusz danych(PDF) 8 Page - Texas Instruments |
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LM13700N Arkusz danych(HTML) 8 Page - Texas Instruments |
8 / 32 page LM13700 SNOSBW2E – NOVEMBER 1999 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Figure 20. Leakage Current Test Circuit Figure 21. Differential Input Current Test Circuit Circuit Description The differential transistor pair Q4 and Q5 form a transconductance stage in that the ratio of their collector currents is defined by the differential input voltage according to the transfer function: (1) where VIN is the differential input voltage, kT/q is approximately 26 mV at 25°C and I5 and I4 are the collector currents of transistors Q5 and Q4 respectively. With the exception of Q12 and Q13, all transistors and diodes are identical in size. Transistors Q1 and Q2 with Diode D1 form a current mirror which forces the sum of currents I4 and I5 to equal IABC: I4 + I5 = IABC (2) where IABC is the amplifier bias current applied to the gain pin. For small differential input voltages the ratio of I4 and I5 approaches unity and the Taylor series of the In function can be approximated as: (3) (4) Collector currents I4 and I5 are not very useful by themselves and it is necessary to subtract one current from the other. The remaining transistors and diodes form three current mirrors that produce an output current equal to I5 minus I4 thus: (5) The term in brackets is then the transconductance of the amplifier and is proportional to IABC. Linearizing Diodes For differential voltages greater than a few millivolts, Equation 3 becomes less valid and the transconductance becomes increasingly nonlinear. Figure 22 demonstrates how the internal diodes can linearize the transfer function of the amplifier. For convenience assume the diodes are biased with current sources and the input signal is in the form of current IS. Since the sum of I4 and I5 is IABC and the difference is IOUT, currents I4 and I5 can be written as follows: (6) Since the diodes and the input transistors have identical geometries and are subject to similar voltages and temperatures, the following is true: 8 Submit Documentation Feedback Copyright © 1999–2013, Texas Instruments Incorporated Product Folder Links: LM13700 |
Podobny numer części - LM13700N |
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