The circuit breaker is generally used at the transmitter. It combines two or more radio signals sent from different transmitters into an RF device transmitted by the antenna. At the same time, the interaction between signals at different ports is avoided.

A circuit breaker typically has two or more input ports and only one output port.Port isolation is an important indicator that describes the capability of two signals not to affect each other. The port isolation must be greater than 20dB.

The 3dB bridge has two input ports and two output ports. It is used to combine the two wireless carrier frequencies and feed them to an antenna or distribution system.If only one outlet is used, the other outlet needs to be connected with 50W dummy load. In this case, the signal has 3dB loss after joining.Sometimes both output ports are used, in which case no load is required and no 3dB loss is required.

Combine the reception and transmission of a cell phone into a single antenna.In a GSM system, because the sending and receiving are not in the same time slot, the cell phone can eliminate the need for a diplexer to isolate the sending and receiving signals. Instead, a simple sending and receiving circuit breaker can be used to combine the sending and receiving signals to a single antenna without interfering with each other.

For the receiving circuit, the antenna receives the signal down, enters the receiving channel through the circuit breaker, mixes the frequency with the received local oscillator signal (that is, the received VCO signal generated by the frequency synthesizer), turns the high frequency signal into the intermediate frequency signal, and then performs the orthogonal demodulation of the signal to generate the received I, Q signal;Then the GMSK (Gaussian Filter minimum frequency shift keying) demodulation transforms the analog signal into a digital signal, which is then fed into the baseband processing unit.

For the transmit circuit, the TDMA frame data stream (rate is 270.833kbit/s) is sent from the baseband part for GSMK modulation to form the transmit I and Q signals, which are then sent to the transmitter upconverter for modulation to the transmit frequency band, and then transmitted by the antenna after power amplification.

The frequency synthesizer provides the local oscillator signal necessary for frequency conversion to the transmitting and receiving units, and uses phase-locked loop technology to stabilize the frequency. It obtains the frequency reference from the clock reference circuit.

The clock reference circuit is usually 13MHz clock. On the one hand, it provides the clock reference for frequency synthesis circuit, and on the other hand, it provides the working clock for logic circuit.