What are opamps?

Op Amps are basic building blocks of analog circuits. They are used in several signal conditioning tasks such as voltage amplification, filtering, and mathematical operations. An important characteristic of an op amp is its speed. Ideally, op amps function infinitely fast with infinite gain at all frequencies, but in reality, they have finite speeds.

But, what causes an op amp to have finite speed in the first place? This happens because real life op amps are limited by finite impedances at nodes. Impedance at a node is determined by the amount of resistance and capacitance at a node. As frequency increases, capacitance behaves more like a “short” leading to lower impedances and hence lower gains. Eventually, a point comes when the signal starts getting “lost”. It is this point which limits how fast an op amp can work.

Characteristics and Functions of Three Operational Amplifiers

A difference amplifier is the first known application of the Op Amps. The original function of the op-amp was to take two small voltage inputs, in the presence of large common-mode voltage. The difference between the two small inputs was amplified when going through the three stages of the op-amp.

Being able to detect and amplify small differences in signals has many uses within analog circuit blocks. Vital signals in your design may be small and you may want to amplify them so you can send their information to a controller or some other circuit block that requires a larger signal. A difference op-amp can be a good choice for this application.

A current-sense amplifier measures and amplifies a very small voltage at its inputs. The small voltage is developed across a current-sense electrical device, external and upstream of the op-amp. The amplifier outputs a voltage proportional to the current flowing in the sense resistor. Amplifying a small voltage on its inputs is done in the presence of very high common-mode voltages.

A current sense Op Amps is characterized by its ability to withstand high input voltages that are higher than the op-amp rails. When the input voltages present on the op-amp inputs is greater than the op-amp rails, the amplifier powers itself from the input common-mode voltages present. To allow high voltage on its inputs, this type of op-amp employs specialized ESD structures to prevent damage to the part.

A transimpedance amplifier is employed as a current-to-voltage convertor. It is useful when wanting to amplify signals from upstream circuits or components whose current is more linear than its voltage. Devices whose current is a lot of linear than their supply voltage ar usually diodes. Sensing devices usually use diodes to discover close lightweight or to sense a collision. The current signal of these sensors is linear and easier to process, so a transimpedance amplifier is used to amplify and deliver its signal downstream in the system.

A few common terms encountered once using op-amps are:

Bandwidth: The band of frequencies over that the gain of the amplifier is sort of constant.

CMRR: Common-mode rejection ratio is the ability of the amplifier to reject common signals present on both inputs of the amplifier.

Gain: The amplitude of magnification to the input signal.

Linearity: When the output signal is directly proportional to the input signal.

Precision Resistor: AN actual part that doesn’t drift a lot of from its par value.

Quiescent Current: Quiescent current is the average current the amplifier will use when off.

Reference Voltage: A constant voltage provided to the amplifier which doesn’t change when loaded, under temperature changes, the passage of time, and/or power supply variations.

Slew Rate: The maximum rate of time it takes for a signal to become present on the output of an op-amp.