WORKING PRINCIPLE OF COUPLER

Coupler is extracted from the RF device a small part of the signal from the wireless signal of main channel, as shown in Figure 2, all belong to the power distribution device and power splitter, coupler is different is the unequal power distribution device. Coupler and power divider using collocation, mainly in order to achieve a goal – the transmit power signal source can be equally assigned to each antenna of indoor distribution system, the transmit power of each antenna is basically the same.

Coupling degree and insertion loss are the important indexes of coupler. Coupling degree is the ratio of the coupling port to the input port, and the dB is generally negative. The greater the absolute value of the coupling degree, the less the equivalent of taking away, the smaller the loss of the natural coupler. Insertion loss is the ratio of the output port to the input port. The greater the absolute value of the coupling degree, the lower the absolute value of the insertion loss.

Example:

A coupler coupling – 10dB, the insertion loss of it – 0.5dB. Take the absolute value, and then take into account the dielectric loss, the average insertion loss will be greater, different manufacturers are not the same, the average insertion loss of about 0.7dB.

If the input port power is 15dBm, then the power of the coupler’s coupling port is 15dBm-10dB=5dBm, and the power of the output port is 15dBm-0.7dB=14.3dBm.

In this many people will ask such a question: 5dBm+14.3dBm>15dBm, energy is not conserved, why is the reason is very simple, with dBm as the number of units can not be added.

In the photoelectric coupler with input signal to send light source, light intensity up to the excitation current size, the light to the light receiving device package together after the photocurrent was produced because of the photoelectric effect, led by a light output end, so as to realize the electric light electric. Conversion.

Work characteristics (in the case of photosensitive transistor)

The internal common mode rejection ratio is high. Because the coupling capacitance between the light emitting diode and the light receiving device is very small (less than 2pF), the common mode input voltage has little effect on the output current through the pole coupling capacitance, so the common mode rejection ratio is very high.

output characteristic

The output characteristics of the photoelectric coupler is refers in the light emitting current is IF, the relationship between the photodiode bias voltage VCE and the output current of IC, when IF=0, the light emitting diode does not emit light, the photosensitive transistor collector output current is known as the dark current is generally small. When IF>0, under a certain IF, the corresponding IC is essentially independent of VCE. The change of IC and IF is linear, and the output characteristic of the photoelectric coupler is similar to that of common crystal.

Photoelectric coupler can be used as a linear coupler

Provide a bias current in the light-emitting diode, then the signal voltage to the light emitting diode through a resistor coupled transistor, so the received optical signal is on the increase and decrease in the bias current changes, the output current signal with input voltage linearly. The photoelectric coupler can also work in the switch state, and transmits the pulse signal. There is a delay time between the input signal and the output signal when the signal is transmitted. The input and output delay time of the different structure of the optical coupler is very large.