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Operating Principle Of Coupler
Aug 19, 2017

Operating principle of coupler

Principle analogy:

Zhang of the north and south sides of the Chinese cabbage every 3 copies, Zhang hopes to obtain each one-time channel changes, a small part of the flow from the main channel, the water flow velocity and the other to try the same, so Zhang can take time in the shade, do not do any of the channel changes, all at the same time jiaowan.

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 - to 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.

The input port power of the ideal coupler is equal to the sum of the power of the coupled port and the output port, and the Watt (W) is the unit, that is, the important indexes of the coupler are coupling degree and insertion loss. The coupling ratio is the ratio of the power between the coupled port and the input port, and is generally negative if expressed in dB. The greater the absolute value of the coupling, the less the amount taken, the smaller the loss of the natural coupler. The insertion loss is the ratio of the output port to the input port. The greater the absolute value of the coupling degree, the smaller the absolute value of the insertion loss.

In the case of dB, the following relationships apply:

Then, the relationship between the insertion loss (dB) and the coupling degree (dB) of the coupler can be expressed as:

Example:

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

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

Here, many people ask this question: 5dBm+14.3dBm>15dBm, energy is not conserved. Why? The reason is simple. The number of units in dBm cannot 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.

The work characteristics (for example to phototriode)

The internal common mode rejection ratio of optocoupler is very high. Because the coupling capacitance between the LED and the receiver is very small (less than 2pF), the common mode input voltage has very little influence on the output current through the interelectrode coupling capacitor, so the common mode rejection ratio is very high.

The output characteristics

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 certain IF action, the corresponding IC is essentially independent of VCE. The relationship between the IC and the IF is linear, and the output characteristics of the optocoupler measured by the semiconductor tube characteristic plotter are similar to the output characteristics of the common crystal triode.

3 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 optocoupler can also operate in switching mode to transmit pulse signals. When the pulse signal is transmitted, there is a certain delay time between the input signal and the output signal, and the input and output delay time of the optocoupler is very different.


CenRF Communications Limited
Add:9F, Dongguan Building, Jiangnan Ave 4288, Binjiang District, Hangzhou
Contact:Alan Huang
Tel: +86-571-86631886
Fax: +86-571-89930536
Mobile: +86-18969122786
E-mail: sales@cenrf.com

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