Audio Applications for Op Amps, Part I
by Bruce Carter
Advanced Analog Products, Op amp Applications
Texas Instruments, Incorporated
Introduction
This is the first of three articles in a series on audio circuits with the
focus on new operational amplifiers that have excellent audio performance
and can be used in high performance applications.
There have been many earlier collections of op amp audio circuits but all of them use split supplies. Many times, the designer who has to operate a circuit from a single supply does not know how to perform the conversion. Single-supply operation requires a little more care than split-supply circuits.
Split Supplies Vs. Single Supply
All op amps have two power pins. In most cases, they are labeled VCC+
and VCC-. Sometimes, however, they are labeled VCC
and GND. This is an attempt on the part of the data sheet author to categorize
the part as a split-supplies or single-supply part. It does not mean, however,
that the op amp has to be operated that way. It may or may not be able to
operate from different voltage rails. Consult the data sheet; especially
the absolute maximum ratings and voltage-swing specifications, before operating
at anything other than the recommended power supply voltage(s).
Most analog designers know how to use op amps with a split power supply. The power supply consists of a positive supply and an equal and opposite negative supply. The most common value is +/-15 V, but +/-12 V and +/-5 V are also used. The input and output voltages are centered and referenced to ground and swing both positive and negative to VOM+/-, the maximum peak-output voltage-swing.
A single-supply circuit connects the op amp power pins to a positive
voltage and ground. The positive voltage is connected to VCC+,
and ground is connected to VCC- or GND. A virtual ground, halfway
between the positive supply voltage and ground, is the "ground"
reference for the input and output voltages. Voltage swings above and below
this virtual ground to VOM+/-;. Some newer op amps have different
high and low voltage rails
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