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Buffer Amplifiers
Georgia Institute of Technology
CS 3651 – Prototyping
Intelligent Appliances
Buffer Amplifiers
Terms and their specific meanings:
Voltage, current, resistance, impedance, etc.
What is a Buffer Amplifier?
Two types, current and voltage
What do they do?
What are some examples?
Analog-to-Digital converters
23 January 2009
1
Terms
Voltage – The difference in electrical potential between
two points, i.e. the line integral of the relative field strength
of the two points.
Current – The flow of electrical charge.
Resistance – opposition of current flow, DC.
Impedance – opposition to current flow, AC.
Power – Amount of energy delivered over time.
What is a buffer amplifier?
“A buffer amplifier (sometimes simply called a buffer) is one
that provides electrical impedance transformation from one
circuit to another. Two main types of buffer exist: the voltage
buffer and the current buffer.” (picture and quote from Wikipedia)
This means that by using a
difference in impedance, the current or
voltage can be transformed.
The capital alpha and beta symbols
represent the voltage and current gain,
respectively.
Voltage Buffer
Typically used to transfer voltage from a circuit current
with high impedance to a circuit current with low
impedance.
This prevents the second circuit from being overloaded by
the first
Could be disastrous to any circuit.
The ideal buffer has an infinite input impedance and zero
output impedance.
Unity gain buffer
Gain coefficient of 1
Even though voltage gain is 1, usually current is boosted,
which means more power. Why? (I’m not sure )
Voltage Buffer (cont’d)
What does the circuit do?
This allows the output to draw more voltage without drawing
it directly from the source, rather from a “reserve”
Prevents the output from drawing too much and overloading
the circuit
Since the source isn’t being tapped, which means the
current doesn’t rise, less power is used and less heat is
created (if any at all)
This is just a unity gain voltage
buffer.
Current Buffer
Typically used to transfer current from a circuit with low
impedance to a circuit with high impedance.
This prevents the second circuit from being overloaded by
the first
Could be disastrous to any circuit. (Again!)
The ideal buffer has a zero input impedance and infinite
output impedance.
Unity gain buffer
Current Buffer(cont’d)
Example:
Imagine you want to have some device that has a high
output current, but your computer would blow up if it
received that much current.
Too much current can cause wires to melt and fuse, or
ignite its surroundings.
By using a current buffer with a gain coefficient of < 1, the
impedance can be used to reduce the current to levels
which are safe for the computer
The number of situations in which these buffers are useful
is without end.
Analog-to-digital converters (ADC converters)
“An electronic device that converts an input analog
voltage (or current) to a digital number.”
Wikipedia
The simplest form of output is binary, but other forms can
be used, such as Gray code or two’s complement binary.