Buffer Amplifiers

1. Buffer Amplifiers Georgia Institute of Technology

2. 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

3. 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.

4. 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.

5. 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 )

6. 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 voltagebuffer.

7. 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

8. 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.

9. 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.