What Is a Step Attenuator?
An attenuator is a circuit or device that can attenuate a signal by a specified amount without distorting it.
There are two types of attenuators: fixed and continuously variable attenuators, in addition to step attenuators.
A fixed attenuator attenuates the signal by a fixed amount, while a variable attenuator can vary the attenuation linearly, and a step attenuator can vary the attenuation in steps.
Although there are several types of attenuators, the purpose of attenuating signals remains the same. Therefore, in the following explanations, unless otherwise specified, all explanations will be common to all attenuators. Expressions such as step attenuator will only be used when necessary.
Uses of Step Attenuators
Typical applications of attenuators are signal level adjustment and impedance matching.
Suppose the signal level is too high for the input signal when connecting to a subsequent circuit or device. In that case, it is used as a signal level adjustment function to adjust the signal level to an appropriate level and send it to the subsequent stage.
If the impedances of the sender and receiver do not match when an input signal connects to a circuit in a subsequent stage, noise or signal reflection may occur, which may result in inconvenience to the expected operation. The step attenuator is used as an impedance-matching function to prevent such inconveniences.
Principle of Step Attenuators
An attenuator has a structure called a T-type circuit or N-type circuit that combines resistors.
In addition, to obtain a specified amount of attenuation, a T-type or N-type circuit may be configured by connecting multiple stages of each of these circuits in a dependent manner.
If the purpose is to attenuate the signal, the objective can be fulfilled by inserting an appropriate resistor.
For example, consider the case of a TV receiver used to measure the reception performance of TV broadcasts.
The reception conditions may be made worse by attenuating the strength of the incoming radio signal in steps using a step attenuator. The receiver evaluates the level of input signal attenuation to see if it can be received without problems and if the amount of attenuation meets the design target value.
In this case, digital terrestrial broadcasting sends broadcast signals in the 470 to 710 MHz range, and these frequencies are input to the TV set. Therefore, since it is necessary to attenuate the signal flatly at all frequencies, resistors cannot be used for this type of test, and a step attenuator is required.
Thus, attenuators in high-frequency circuits must attenuate while maintaining impedance.