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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
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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