A tuned amplifier is an

electronic amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a Signal (information theory), signal (a time-varying voltage or Electric current, current). It may increase the power (physics ...

which includes

bandpass A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. Description In electronics and signal processing, a filter is usually a two-port ...

filtering components within the amplifier circuitry. They are widely used in a variety of wireless applications. Stagger-tuned 3-stage amplifier

Schemes

There are several tuning schemes in use, *

Staggered tuning Staggered tuning is a technique used in the design of multi-stage tuned amplifiers whereby each stage is tuned to a slightly different frequency. In comparison to synchronous tuning (where each stage is tuned identically) it produces a wider Band ...

where each amplifier stage is tuned to a slightly different frequency. * Synchronous tuning (explained in more detail in the staggered tuning article) where each amplifier stage is tuned identically. This scheme maximises the amplifier gain but has narrower bandwidth than staggered tuning. *

Double-tuned amplifier A double-tuned amplifier is a tuned amplifier with transformer coupling between the amplifier stages in which the inductances of both the primary and secondary windings are tuned separately with a capacitor across each. The scheme results in a w ...

. This scheme is used on amplifier stages that are

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

-coupled rather than capacitor coupled. Both the primary and secondary coils of the transformer are tuned. This has the effect of widening the bandwidth. Other tuning schemes are sometimes called single-tuned to distinguish them.

Variable tuning

The RF amplifier stages of radio receivers require variable tuning to select the station, usually achieved by using

variable capacitor A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically. Variable capacitors are often used in L/C circuits to set the resonance frequency, e.g. to tune a radio (therefo ...

s in the resonant circuits. The tuning of all stages of the RF amplifier have to be kept in step along with the frequency of the

local oscillator In electronics, a local oscillator (LO) is an electronic oscillator used with a mixer to change the frequency of a signal. This frequency conversion process, also called heterodyning, produces the sum and difference frequencies from the frequenc ...

. This may be done by mechanically linking the capacitors, or electronically using

varicap In electronics, a varicap diode, varactor diode, variable capacitance diode, variable reactance diode or tuning diode is a type of diode designed to exploit the voltage-dependent capacitance of a reverse-biased p–n junction. Applications Vara ...

diodes as capacitors. Since linked tuning becomes more difficult as the number of stages increase, the number of RF stages is kept to a minimum with most of the tuning happening in the IF stages. The

IF amplifier Intermediate-frequency (IF) amplifiers are amplifier stages used to raise signal levels in radio and television receivers, at frequencies intermediate to the higher radio-frequency (RF) signal from the antenna and the lower (baseband) audio or v ...

operates at a fixed frequency making tuning much easier.Carr, pp. 8–10

References

* Carr, Joseph J., ''The Technician's Radio Receiver Handbook'', Newnes, 2001 . * Pederson, Donald O.; Mayaram, Kartikeya, ''Analog Integrated Circuits for Communication'', p. 259, Springer, 2007 . * Gulati, R. R., ''Monochrome and Colour Television'', p. 432, New Age International, 2007 {{ISBN, 8122416071. Amplifiers Signal processing filter