Editing Amplifier (section)

=== Frequency range ===
{{Unreferenced section|date=December 2024}}
Depending on the frequency range and other properties amplifiers are designed according to different principles.

Frequency ranges down to DC are used only when this property is needed. Amplifiers for direct current signals are vulnerable to minor variations in the properties of components with time.  Special methods, such as [[chopper (electronics)|chopper]] stabilized amplifiers are used to prevent objectionable drift in the amplifier's properties for DC. "DC-blocking" [[capacitor]]s can be added to remove DC and sub-sonic frequencies from audio amplifiers.

Depending on the frequency range specified different design principles must be used. Up to the MHz range only "discrete" properties need be considered; e.g., a terminal has an input impedance.

As soon as any connection within the circuit gets longer than perhaps 1% of the wavelength of the highest specified frequency (e.g., at 100&nbsp;MHz the wavelength is 3&nbsp;m, so the critical connection length is approx. 3&nbsp;cm) design properties radically change. For example, a specified length and width of a [[Printed circuit board|PCB]] trace can be used as a selective or impedance-matching entity.
Above a few hundred MHz, it gets difficult to use discrete elements, especially inductors. In most cases, PCB traces of very closely defined shapes are used instead ([[stripline]] techniques).

The frequency range handled by an amplifier might be specified in terms of [[Bandwidth (signal processing)|bandwidth]] (normally implying a response that is 3&nbsp;[[Decibel|dB]] down when the frequency reaches the specified bandwidth), or by specifying a '''frequency response''' that is within a certain number of [[decibel]]s between a lower and an upper frequency (e.g. "20&nbsp;Hz to 20&nbsp;kHz plus or minus 1&nbsp;dB").