Limiter Circuits

The function of the limiting circuit is to limit the output signal amplitude within a certain range. That is, when the input voltage exceeds or falls below a certain reference value, the output voltage will be limited to a certain level (called the limiting level) and will no longer change with the input voltage.

1. Diode limiter

In the limiting circuit shown in Figure T1606, since the diode is connected in series between the input and output, it is called a series limiting circuit.

In the figure, if the diode has an ideal switching characteristic, then when u _i is lower than E , D is not conducting, u . = E ; when u _i is higher than E , D is conducting, u _O = u _i . The limiting characteristic of the limiter is shown in Figure T1607 . When the input amplitude is greater than the sine wave of E , the output voltage waveform is shown in Figure T1608 . It can be seen that the circuit limits the lower limit level of the output signal to a certain fixed value E , so this limiter is called a lower limiter. If the polarity of the diode in the figure is reversed, an upper limiter that limits the upper limit level of the output signal to a certain value is obtained.

If the diode and the load are connected in parallel, a parallel limiter is formed, see Figure T1609.

In the figure, when u _i is higher than E , D is turned on, u _o = E ; when u _i is lower than E , D is turned off, u _o = u _i . Its limiting characteristics are shown in Figure T1610 . Obviously, this is an upper limiter.

Combining the upper and lower limiters together forms a bidirectional limiter circuit as shown in Figure T1611 , and its limiter characteristics are shown in Figure T1612 . When a sinusoidal signal with a large amplitude is input, the output waveform is shown in Figure T1613 .

2. Transistor limiter

The cut-off and saturation characteristics of the triode can also be used to form a limiting circuit (as shown in Figure T1614). This type of circuit also has an amplification function. In order to meet some higher technical requirements, an integrated operational amplifier can also be used to form a limiting circuit.