Operational Amplifiers and Other Integrated Circuit Usage Jimmie Fouts Houston County Career Academy

What is the Op-Amp One of the most versatile electroinic circuits! Utilizes external feedback to control response Normally operates at high gain, high input impedance, low output impedance, and wide bandwidth Most common integrated circuit is the 741 (LM 741, NE 741, µA 741)

History The term Op-Amp originated in 1943 by Ragazzinni and Philbrick Early Op-Amps were introduced in 1952 and consisted of electron tubes Modular, solid state devices introduced in 1963 by Fairchild Semiconductors The first solid state device was the µA 702

µA 702 Integrated Circuit Manufactured by Fairchild First solid-state monolithic circuit Used +12 and – 6 VDC power supplies Quick to “burn out” if shorted! Contained only 9 transistors Cost was $300. in 1963 dollars!

µA 709 Introduced by Fairchild in 1965 Higher gain, larger bandwidth, lower input current than the µA 702 More user friendly power requirement of +/- 15 VDC High production demands resulted in initial price of $70 per IC By 1969, they were so common that they were selling for around $2 each

National Semiconductor Widlar, the original developer of the Fairchild ICs, developed the LM 101 in 1967 The LM 101 was more versatile –Included short circuit protection –Frequency compensation –Later versions included temperature compensation and offset compensation

Continued Development Over time the basic µA 741 has continued to develop Other manufacturers have produced similar versions Raytheon began producing a chip with quad op-amps in 1974 National Semiconductors produced the quad version (LM 324) also RCA begin making it with an FET input for extremely low input current requirements

Specification Sheets Device specification sheet identify key information about the device Most important is the Pin Layout

The IC Pin Layout Defines the pin layout of the integrated circuit Most important to troubleshooting a circuit with an IC Eliminates the need for a detailed schematic of the internal makeup of the IC The chip marking/indent on top identifies Pin 1 With Pin 1 in the upper left, pins are numbered down, then to the left, then up

Absolute Maximum Parameters Supply Voltage –Maximum safe +/- input voltage Dissipation –Maximum allowable power Input Voltage –Maximum signal input allowed Differential Input –Maximum + and – input voltage allowed

Input Parameters Input Offset Voltage –Voltage required for 0 volt output Input Bias Current –Average current flow through both inputs Input Resistance –Resistance on the input with other input grounded Input Voltage Range –Range of common- mode input signals

Output Parameters Output Resistance –Resistance seen at the output Output Short Circuit Current –Maximum output current Output Voltage Swing –Peak output voltage without clipping

Dynamic Parameters Open Loop Voltage Gain –Voltage ratio output to input Large Signal Gain –Maximum swing to drive output from 0 to a specified voltage Slew Rate –Time rate of change in output for a gain of 1

Other Parameters Supply Current –Current required from the power source Common Mode Rejection –Ability to reject signals presented at both inputs simultaneously Channel Separation –Ability to reject “crosstalk”/other signals on same chip Open Loop Gain –Output gain vs. frequency

741 Integrate Circuit Pin Function Pin 1 – Used to minimize offset Pin 2 – Inverted signal to output Pin 3 – Non-inverted signal to output Pin 4 - Vcc ´ - Negative power supply input Pin 7- Positive power supply input Pin 5 – Used to minimize offset Pin 6 – Output Pin 8 – Not Connected

TRANSITIONAL

µA 741 Fairchild began producing the µA741 in 1968 Similar to the LM 101 it included –An on-chip capacitor for frequency compensation –Temperature compensation –Higher speed –Lower input current

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