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Op Amp Ideal Device


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Ideal Operational Amplifier Properties

Characteristics Ideal Real - Depends on the model
GAIN: Open Loop Infinity > 100000 or 1000000 typical
Input Resistance: (Impedance) Infinity > 1M (Bipolar) > 1000M (FET)
Output Resistance: (Impedance) Zero 100 - 1000R
SATURATION High:
Highest Output Voltage
Positive Power Supply Voltage

Typical value = 12 V.

Two volts below the positive supply

Typical value = 10 V.

SATURATION Low:
Lowest Output Voltage
Negative Power Supply Voltage

Typical value = -12 V.

Two volts above the negative supply

Typical value = -10 V.

Gain Bandwidth Product: Infinity 1 - 20MHz
Input offset voltage: Zero Often Adjustable to Zero

Saturation

Clipping or Limiting

The image below shows ideal (black) and non-ideal (red and blue) behaviour including clipping when the op amp is saturated and the output voltage can go no higher.

Saturation.gif

Amplifiers increase the magnitude of the input signal.

Gain is a number (with no units) used to describe how much bigger a signal becomes when it is amplified.

Amplifier Gain.gif

Amplifiers have one or more of the following properties.

Voltage Bandwidth

The voltage bandwidth of an op amp is the frequency over which the output is at least 70% (0.7) of the maximum output voltage of the circuit.

Power Bandwidth

The power bandwidth of an op amp is the frequency over which the output is at least 50% (0.5) of the maximum output power of the circuit.

The 741 Operational Amplifier

Pinout

Op Amp 741.gif

Pins

  1. Offset Null - Rarely used. It can be used to to adjust for small errors in the two inputs so zero volts in gives zero volts out.
  2. Inverting Input - If this voltage increases, the output voltage will go DOWN unless the Op Amp is already saturated.
  3. Non-Inverting Input - If this voltage increases, the output voltage will go UP unless the Op Amp is already saturated.
  4. The minus supply - Sometimes this is connected to zero volts ( ground ). Sometimes it's connected to a voltage between -5V and -18V.
  5. Offset Null - Rarely used. It can be used to to adjust for small errors in the two inputs so zero volts in gives zero volts out.
  6. The Output - In an ideal Op Amp, the maximum and minimum output voltage is equal to the power supply voltages. In a real life Op Amp, these voltages are about 2 to 3 Volts less.
  7. The plus supply - Voltages from +5V to +18V are common. There are specialist and more expensive Op Amps with a higher voltage ratings.
  8. No Connection - This pin is not used.

Data Sheet

The 741 is a low cost operational amplifier. It has ...

It can be used to make ...

 

 

 

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