Operational Amplifiersand Other Integrated Circuit Usage

Jimmie FoutsHouston 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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