Illustrated Dictionary of Electronics
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Distribution Amplifier

In general terms a Distribution Amplifier is a piece of equipment that accepts an input signal and outputs that signal to a number of outputs. Although a distribution amplifier may accept different input channels and output those to particular outputs. The term is meant to describe something that outputs the same signal to some number of outputs, based on one input. The outputs are identical, and the signals all appear or transition at the same time.

A similar approached is used with some IC functions, an example would be a 1-to-10 Clock Buffer, used for clock distribution. Many other logic functions exist to provide minimum signal skew between outputs and eliminate the fanout problem of driving multiple outputs. IC Decoders are another form of signal distribution. Semiconductor Analog Switches are also used to distribute, or fan out signals to more than one location.

As a piece of equipment, a distribution amplifier could come in many forms. The distribution amplifier might be designed to fan-out audio signals, video signals or digital signals, and in each case being a completely different design. At the circuit level the amplifiers, or drivers, could be 50 ohm or 75 ohms and might be called lines drivers or cable drivers.

At the circuit level the distribution amplifier would take on the form of the clock buffer example but would use ICs of what ever type would have the correct interface level. For example TTL ICs for digital logic signals or operational amplifiers for analog signals.

Audio range distribution amplifier using a TL084 operational amplifier
Distribution Amplifier

The circuit fragment above is meant to represent a distribution amplifier used in the audio range. The capacitor values have been selected to have an effect in the audio frequency range, but they could be altered to change the frequency range. The operational amplifier used in the circuit is a TL084 which has a unity gain bandwidth of 3Mhz.

The TL084 was selected because it's a quad package and carries all four of the required operational amplifiers. However any operational amplifier, including a 741 Op Amp, would work as long as the bandwidth of the amplifier matched that of the frequency of interest. The data sheet indicates a 14 pin DIP package or 20 pin flat pack, which indicates the age of the device [no SOIC option].

The first operation amplifier is intended to be a preamplifier and has a gain of ten. However the gain may be changed by adjusting either the 1Meg or 10k resistors. The input is applied through a 1uF capacitor to block any DC from the previous stage. However as this component may not be required, or reside in the preceding circuit, so may be left out. The three distribution amplifiers are each unity gain voltage followers.

The circuit diagram was modified from an example in an application note, or application book. The original circuit, dating back to the 1980's also used 50uF capacitors and 5.1k load resistors on the output of each of the buffers [neither is shown here].
Reference: Linear and Interface Applications Volume 1, 1985 [TI].

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