Special Uses of Resistors

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Special Uses of Resistors [Copy link]

　In addition to the functions of current shunting, voltage dividing, voltage reduction and current limiting, resistors also have the following functions.

l Level adjustment.

When the level at a certain point in the transmission equipment changes, the T-type attenuator shown in Figure 1 can be adjusted to meet the requirements. The attached table lists the calculation data of the attenuator with a characteristic impedance of 1Ω. When looking up the table, just find the level value of the attenuator to be designed, and multiply the impedance required by the corresponding R1 and R2 data in the table, which is the actual R1 and R2 values of the attenuator required.

For example: to design an attenuator with an impedance of 75Ω and an attenuation value of 10dB, we can get the following by looking up the table:

R1=0.5195*75=39.0Ω

R2=0.7027*75=52.1Ω.

1. Impedance matching.

Figure 2 shows an impedance matching attenuator composed of resistors. Connecting the attenuator between two networks with different characteristic impedances can achieve impedance matching, where:

R1=√Zc1 (Zc1-Zc2) (?)

R2= Zc2√Zc1 / (Zc1-Zc2) (?)

For example: Design an impedance matcher with Zc1=300Ω, Zc2=75Ω as shown in Figure 3.

R1=√300 (300-75) =259.8 ?

R2= 75√300 / (300-75)=86.6?

It should be pointed out that the resistors in the above applications should be non-inductive resistors, and shielding measures should be taken in high-frequency applications. At the same time, attention should be paid to power consumption, that is, working attenuation.