Characteristics of Amplifier

Characteristics of Amplifier
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A generic single stage amplifier configuration
embedded between input and output matching
networks.
The amplifiers is characterized through its s-
matrix at a particular DC bias point.
Amplifier parameters:
Gain and gain flatness(in dB)

Operating frequency and bandwidth(in Hz)
Output power in dB
Power supply requirements
Input and output reflection coefficient (VSWR)
Noise figure in dB
Bandwidth:
Bandwidth is the range of frequencies the device is
intended to work by. Frequency range for radio and
television signals is 47-862 MHz.
Gain:
The gain G is defined as the ratio of the power
delivered to the output to the power available from
the input. The greater the gain, the more the signal is
amplified in the amplifier. Gain is usually expressed in
decibels (dB):
CATV amplifier gain is typically 25-40 dB.

Antenna amplifier gain is typically 10-30 dB.
Gain adjust range:
The range of adjustable gain shows the limits of
adjusting the gain. For example, in case the maximum
gain of an amplifier is 35 dB and the range of adjustable
gain is20 dB, the gain of the amplifier could be adjusted
in the range of 15-35 dB.
Flatness:
In an ideal amplifier all frequencies are amplified equally. This
means that the graph of an ideal gain depending upon frequency is
absolutely flat. This is never achieved in real amplifiers and there is
always some difference from the overall flatness that is expressed in
decibels.
The flatness of amplifiers is typically 12 dB, in high quality
amplifiers 0.50.6 dB.
Noise Figure:
Every amplifier amplifies both the signal and the noise
delivered to the input. Since an amplifier is never ideal, it
also adds some self-noise during the amplifying process and
therefore in the amplifier output there is a sum of amplified
input noise and amplifier self-noise in addition to the
amplified signal.
Thus, the signal-to-noise ration always decreases between
amplifier input and output. This decrease is expressed by
noise figure (NF) and is calculated in decibels:
The lower the noise figure, the lower the amplifier self-
noise is. Noise figure is different for different
frequencies, therefore for wideband devices (CATV
amplifiers) many NF values are often given.
Typically NF = 49 dB, in low noise amplifiers (LNA) NF =
0.52 dB.
Cascading amplifiers:
Noise figure of cascaded amplifiers is expressed by the
formula:
in which Fn is the amplifier noise figure, Gn is the

amplifier gain and n is the amplifier order number in a
cascaded circuit.
Power supply:
There are two parameters that describe the power of a device
nominal voltage and current use. Nominal voltage is the required
and the only allowed voltage the device may be supplied with.
Home devices usually use the voltage of 220 V. If the nominal
voltage of a device is lower (e.g.1617 V for Rantelon amplifiers), a
proper power adapter needs to be used.
Current use shows which current the device uses for work. It is
expressed in milliamperes (mA). In case a power adapter is used
with the device, it must be guaranteed that the maximum allowed
current of the adapter is not lower than the current use of the
device.
In order to calculate the energy in kilowatt-hour, one can use the
following formula:
Maximum output level:
Every amplifier has a limit of maximum output signal level.
Increasing the input signal level, the output signal level also
increases until maximum output level is achieved, one that
cannot be exceeded.
If the input signal level is too high and output signal is at
maximum output level, then the shape of the signal, called
the waveform, is not amplified correctly. This causes signal
distortion and lowers the quality of CATV picture.
It is therefore required to keep input signal level in an
allowed range. The task is simple if there is only one signal in
input, but in CATV systems voice, picture and colors are
delivered simultaneously in many channels. The sum of all
signals must be kept low enough to prevent amplifier from
exceeding maximum output level.

Characteristics of Amplifier

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Characteristics of Amplifier

Gain and gain flatness(in dB)

CATV amplifier gain is typically 25-40 dB.

in which Fn is the amplifier noise figure, Gn is the

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