The attenuator is a circuit to introduce a predetermined attenuation within a specified frequency range. It is generally indicated by the number of decibels of the attenuation introduced and the ohms of its characteristic impedance. Attenuators are widely used in cable television systems to meet the level requirements of multiple ports. Such as amplifier input, output level control, branch attenuation control. There are two types of attenuators: passive attenuators and active attenuators. The active attenuator cooperates with other thermal elements to form a variable attenuator, and it is used in the automatic gain or slope control circuit in the amplifier. Passive attenuators have fixed attenuators and adjustable attenuators.
The attenuator has only one function, which is to provide attenuation. For example, adding attenuation in front of the receiver can prevent excessive signal power from damaging the receiver, or adding attenuation to the line to simulate the line loss of long-distance transmission and so on. The basic functions of the attenuator are as follows.
1. Adjust the size of the signal in the circuit.
2. In the comparative measurement circuit, it can be used to directly read the attenuation value of the tested network.
3. Improve impedance matching. If some circuits require a relatively stable load impedance, an attenuator can be inserted between this circuit and the actual load impedance to buffer the impedance change.
The types of commonly used fixed attenuators include L-type, T-type, bridge T-type, π-type, and so on. Among those types, L-type is an asymmetric attenuator, which is mainly used for impedance matching. However, T-type, bridge T-type, and π-type are symmetrical attenuators, which are mainly used for attenuation. The classic three types of π-type attenuators, T-type attenuators, and bridge-type attenuators have better attenuation effects. But for high-frequency small signals, it is more suitable to choose π-type or T-type network for passive attenuation network.