(Digital subscriber line) the signal is similar based on the family power line’s network signal and xDSL, because two kind of signals have both used one kind of OFDM (Orthogonal Frequency Division Multiplexing) the form. Two kind of signal’s application systems also need the very big output current, the very wide band width and the good linearity. This design example describes one kind of design to have the xDSL driver’s simple line driver electric circuit, uses transmits the high speed data on the family power line. Figure 1 showed one kind to connect the negative feedback electric circuit in order to be separated the wide band the multi-news number to transmit the family power line’s AD8391 current feedback amplifier. Current feedback’s advantage is: It can cause you in not to realize in the gain-bandwidth product limit situation will increase enhances to is bigger than 1 flexibility. AD8391 has the 60MHz band width, 600V/μs slewing rate and 250 mA output current, thus causes it very suitable to actuate the family power line.
Figure a 1 xDSL driver use current feedback technology forms the highly effective family power line driver.
Shown in Figure 1 the electric circuit to use the 5V power source, has - 2 (RF/RG) the voltage gain, and may actuate 33Ω the load. Each each household’s family power line network loaded impedance difference is very big, what 33Ω load simulation is the family power line network worst impedance. The driver passes the transformer and the power line coupling. Sends in the differential motion power line (firing line and neutral axis) the output amplitude is 2.8V p-p, but the peak value to ratio of the mean value is 4V/V. Feedback resistance RF and gain resistance RG may cause the electric circuit band width and the stability enhances to the greatest degree. This electric circuit acceptable band width approximately is 30 MHz. Between following formula expression current feedback amplifier’s closed loop band width (fCL), RG and RF relations:
Internal capacitance CP may establish the split-ring mutual impedance function the corner frequency. RIN is each amplifier input end’s input impedance (in Figure 1 has not drawn CP and RIN) but actually. It is noteworthy that RF is controlling the above formula, thus control closed loop band width. Electric circuit input end 49.9Ω resistor termination in supply oscillator. You must act according to each application system to make the adjustment to the above parameter value. 4 0.1μF capacitors provide the input output line the exchange. The spike is one compound profile which is composed of 75 pseudo-random phase sine wave. Tests in the profile each single tonality possibly to have in four phase one, simulates QPSK (quaternary phase-shift keying modulation) the signal. Between various sine waves’ orthogonal gap is 4 ~ 21 MHz, thus vacates the ham radio frequency band. Figure 2 indicated that in the worst situation the spatial sound distortion is 35 dBc. This chart is suitable for the majority practical power line application system. Figure 3 showed the time domain output.
Figure 2 Shown in Figure 1 the power line driver’s output frequency spectrum to indicate that in the worst situation the spatial sound distortion is 35 dBc.
Figure 3 this diagram of curves expression power line driver’s time domain characteristic.
