If we connect the output of an op-amp to its inverting input and apply a voltage signal to the noninverting input, we find that the output voltage of the op-amp closely follows that input voltage (I’ve neglected to draw in the power supply, +V/-V wires, and ground symbol for simplicity): As Vin increases, Vout will [...]
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AMPLIFIERS2
Amplifier gain
Because amplifiers have the ability to increase the magnitude of an input signal, it is useful to be able to rate an amplifier’s amplifying ability in terms of an output/input ratio. The technical term for an amplifier’s output/input magnitude ratio is gain. As a ratio of equal units (power out / power in, voltage out [...]
Article3
Sensor : Data Acquisition and Readout
Does the remainder of the system, including any additional amplifiers, filters, data acquisition and readout devices, introduce any limitation that will tend to degrade the sensor-amplifier characteristics? Check: ALL of previous check items, plus Adequate Resolution. Installation Even the most carefully and thoughtfully selected and calibrated system can produce bad data if carelessly or ignorantly [...]
AMPLIFIERS4
Absolute dB scales
It is also possible to use the decibel as a unit of absolute power, in addition to using it as an expression of power gain or loss. A common example of this is the use of decibels as a measurement of sound pressure intensity. In cases like these, the measurement is made in reference to [...]
AMPLIFIERS5
Decibels (amplifier’s gain)
In its simplest form, an amplifier’s gain is a ratio of output over input. Like all ratios, this form of gain is unitless. However, there is an actual unit intended to represent gain, and it is called the bel. As a unit, the bel was actually devised as a convenient way to represent power loss [...]
AMPLIFIERS6
Amplifiers ( controlling signal )
The practical benefit of active devices is their amplifying ability. Whether the device in question be voltage-controlled or current-controlled, the amount of power required of the controlling signal is typically far less than the amount of power available in the controlled current. In other words, an active device doesn’t just allow electricity to control electricity; [...]
Article7
Transistors : Feedback
If some percentage of an amplifier’s output signal is connected to the input, so that the amplifier amplifies part of its own output signal, we have what is known as feedback. Feedback comes in two varieties: positive (also called regenerative), and negative (also called degenerative). Positive feedback reinforces the direction of an amplifier’s output voltage [...]
Article8
Amplifier impedances
Input impedance varies considerably with the circuit configuration shown in Figure below. It also varies with biasing. Not considered here, the input impedance is complex and varies with frequency. For the common-emitter and common-collector it is base resistance times ?. The base resistance can be both internal and external to the transistor. For the common-collector: [...]
AMPLIFIERS9
AMPLIFIERS AND ACTIVE DEVICES : From electric to electronic
This third volume of the book series Lessons In Electric Circuits makes a departure from the former two in that the transition between electric circuits and electronic circuits is formally crossed. Electric circuits are connections of conductive wires and other devices whereby the uniform flow of electrons occurs. Electronic circuits add a new dimension to [...]
Article10
OPERATIONAL AMPLIFIERS : part 2 (The “operational” amplifier)
Long before the advent of digital electronic technology, computers were built to electronically perform calculations by employing voltages and currents to represent numerical quantities. This was especially useful for the simulation of physical processes. A variable voltage, for instance, might represent velocity or force in a physical system. Through the use of resistive voltage dividers [...]
AMPLIFIERS11
AMPLIFIERS AND ACTIVE DEVICES
An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). In order for a circuit to be properly called electronic, it must contain at least one active device. Components incapable of controlling current by means of another electrical signal are called passive devices. Resistors, capacitors, [...]
Article12
Transistors : The common-emitter amplifier
At the beginning of this chapter we saw how transistors could be used as switches, operating in either their “saturation” or “cutoff” modes. In the last section we saw how transistors behave within their “active” modes, between the far limits of saturation and cutoff. Because transistors are able to control current in an analog (infinitely [...]
