One example is when 0 follows a 1 full power for t2

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One example is : When 0 follows a 1 Full power for T/2 . Then return to half power. Remain at that level until a 1 appears. Then drop to zero power for T/2. Then return to half-power. An example appears on the next slide.
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Dr. Joseph C. Palais 10.4 16 Data 1 0 1 1 1 0 1 NRZ t T t Bipolar
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Dr. Joseph C. Palais 10.4 17 Advantage of the Bipolar Code The dc level is constant, regardless of the data. The operation is stable with AGC (automatic gain control) receivers. For RZ, a stream of 0’s causes the AGC system to increase the gain, so the next binary 1 is amplified too much.
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Dr. Joseph C. Palais 10.4 18 R v d i R + - V dc S 1 S 2 Three-level LED circuit P
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Dr. Joseph C. Palais 10.4 19 Zero power : Both switches open i = i 0 = 0 P = 0 Half power : Close switch S 1 i = i 1 = [(V dc - v d ) /R] P = P 1 = P F / 2 Full power : Close switches S 1 and S 2 i = i 2 = [(V dc - v d ) / (R / 2)] = 2i 1 P = P 2 = P F
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Dr. Joseph C. Palais 10.4 20 These results assume: 1. Ideal switches No current when switch is open. No voltage drop when switch is closed. 2. The voltage across the diode (v d ) is the same for half-power and full power operation. Other digital formats Sub carrier formats
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Dr. Joseph C. Palais 10.4 21 10.4.2 Other Digital Formats We will now consider various subcarrier digital formats. They are: 1. Subcarrier OOK 2. Subcarrier FSK 3. Subcarrier PSK These are described on the following slides. Compare them with analog subcarrier formats.
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Dr. Joseph C. Palais 10.4 22 Subcarrier OOK (On Off Keying) 0 1 0 Power t T 2T 3T T SC The subcarrier amplitude determines the bit value. ϖ SC = 2 π f SC = (2 π /T SC ) 0
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Dr. Joseph C. Palais 10.4 23 Subcarrier Frequency Shift Keying (FSK) f 1 f 2 f 1 0 T 2T 3T t 0 1 0 Power The subcarrier frequency determines the bit value. f 1 = 0 f 2 = 1
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Dr. Joseph C. Palais 10.4 24 Subcarrier Phase Shift Keying (PSK) 0 T 2T 3T t 0 1 0 Power The subcarrier phase determines the bit value.
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Dr. Joseph C. Palais 10.4 25 10.4.3 Time Division Multiplexing (Electric Domain) TDM involves interleaving the bits associated with independent channels of information.
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