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AN1500A Datasheet(PDF) 10 Page - Sames |
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AN1500A Datasheet(HTML) 10 Page - Sames |
10 / 27 page AN1500A sames sames sames sames 10/27 11.1.2 Measurement: Echo return loss (according to BAPT223 ZV5) is measured by bridge balance measurement as shown in Fig.3: R1 and R2 must be matched to 0.1%, the measuring equipment must be isolated from earth and should have an input resistance of >25k Ω. Capacitors C1 and C2 must be >10µF. The Telephone under test is supplied by a (high ohmic) current source and measurements are taken in speech mode with a connected handset. Fig. 3: Return loss measurement setup Calculation of results: The sending level, measured in “cal”-position of switch SW is tuned to ps=-10dB950mV= 300mVrms,thus the sinewave generator’s level is -4dB950mV = 600mVrms.The receive level (=pe) is measured in “meas”-position of switch SW. The echo return loss is then calculated by: ardB = ps - pe (ps, pe levels in dB950mV) or ardB = 20* log (ps / pe) (ps, pe levels in mVrms) Fig.4 shows some typical results, measured with the DB1500I demo board with Zref= 600 Ω, Z ref= 220 Ω + 820 Ω//115nF and Zref= 270 Ω + 750Ω//150nF. The board was configured as shown in the schematic, using a single bipolar (2SA1210) line transistor. Fig. 4: typ. return loss measurement results with the DB1500I demo board 12 14 16 18 20 22 24 26 28 30 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900 f [Hz] 600 Ohms 220+820//115nF 270+750//150nF 12 Sidetone cancellation |
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