Op amp Characteristics
Could any one help me to gain a deep understanding about the speed of opamp. Is there any relation between the gain-bandwidth (GBW) of op-amp and its. Just to clarify, an op-amp isn't only a voltage amplifier, it's got loaadds of other The relationship is that, as gain increases, the bandwidth, ie the frequency. Power suppliy requirements. • Open loop voltage gain. • Large signal voltage gain. • Gain bandwidth product. • Input offset current. • Maximum differential input.
Because the operational amplifier, which is grown on a silicon die, has many active components, each one with its own cutoff frequency and frequency response. Because of that, the operational amplifier frequency response would be random, with poles and zeros which would differ from op amp to op amp even in the same family. As a consequence, manufacturers thought of introducing a dominant pole in the schematic, so that the op amp response becomes more predictable.
At the same time, it makes the op amp more user friendly, because its stability in a schematic becomes more predictable. The dominant pole will make the op amp behave like a single-pole system, which has a drop of 20 dB for every decade of frequency, starting with the cutoff frequency.
Such a pole is made with a reactive element, usually a capacitor. The choice of a capacitor on the op amp die is because of the manufacturing process.
An Op Amp Gain Bandwidth Product – Mastering Electronics Design
A capacitor is easier to be grown on silicon, as opposed to an inductor. However, the capacitor value depends on its area, and since the die area is at a premium, capacitors can only be very small, in the picofarads range. Since the pole is made with an RC time constant, we need a large resistor to bring the cutoff frequency at low values, hertz, or tens of hertz.
Without going into details, op amp manufacturers achieve these high resistors with active components, like the input resistance seen in a transistor base. Having said that, the gain bandwidth product shows that the product between the op amp gain and frequency, in any point of the frequency response, is a constant. We can always calculate the bandwidth with the following formula.
This means that, at a gain of one, the bandwidth is 12 MHz, and at the maximum open-loop gain ofthe bandwidth is 12 MHz divided bywhich is 24 Hz. This is the op amp open-loop cutoff frequency.
For example, kHz bandwidth multiplied by a voltage gain of 10 also gives a Gain Bandwidth Product of: Then the Power Bandwidth becomes more relevant. Maximum Differential Input This is the maximum voltage that can be applied between the two inputs, on some devices this can be equal to the supply voltage, but on others it can be considerably less.
Input Resistance This is the resistance looking into the input terminals with the amplifier operating without feedback open loop.
Gain–bandwidth product - Wikipedia
Input Offset Current The currents flowing into the two inputs should ideally both be zero, but for practical op amps, although the input currents are still extremely small, they do exist and may also be different. Unequal currents cause different voltages at the inputs, and when this small difference in voltage is amplified, it causes the output to be other than zero.
To overcome this effect an Input Offset Voltage can be applied between the inputs to correct the output voltage to zero. Temperature Coefficients Both the input offset current and input offset voltage are affected by changes in temperature, and tend to drift higher as temperature increases.
If a square wave is applied to the input of the op amp, the output should also be a square wave. However the fast rising and falling edges of the square wave can tend to cause the amplifier to oscillate for a short time after the rise or fall.
In some op amps, because this compensation is internal, there is no way of altering the slew rate, but others use an external compensation capacitor, and therefore provide the means to control slew rate to some degree. The slew rate also affects sine wave and audio signals as well as square waves. The rate of change of voltages in a sine wave is continually varying, it is changing at its fastest rate as the signal voltage crosses zero, and the rate of change falls momentarily to zero no change at both the positive and negative peaks of the wave.
If the slew rate of the amplifier cannot keep up with the fastest rate of change of the signal, some distortion will be produced. Therefore, to be sure of amplifying large amplitude signals that are most likely to produce large and fast rates of voltage change, an op amp needs to have a sufficiently high value of slew rate to cope with the greatest possible rate of voltage change.#172: Basics of Op Amp Gain Bandwidth Product and Slew Rate Limit