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AFE1103 Datasheet(PDF) 9 Page - Burr-Brown (TI) |
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AFE1103 Datasheet(HTML) 9 Page - Burr-Brown (TI) |
9 / 10 page 9 ® AFE1103 DISCUSSION OF SPECIFICATIONS UNCANCELLED ECHO The key measure of transceiver performance is uncancelled echo. This measurement is made as shown in the diagram of Figure 4. The AFE is connected to an output circuit includ- ing a typical 1:2 line transformer. The line is simulated by a 135 Ω resistor. Symbol sequences are generated by the tester and applied both to the AFE and to the input of an adaptive filter. The output of the adaptive filter is subtracted from the AFE output to form the uncancelled echo signal. Once the filter taps have converged, the RMS value of the uncancelled echo is calculated. Since there is no far-end signal source or additive line noise, the uncancelled echo contains only noise and linearity errors generated in the transmitter and receiver. The data sheet value for uncancelled echo is the ratio of the RMS uncancelled echo (referred to the receiver input through the receiver gain) to the nominal transmitted signal (13.5dBm into 135 Ω, or 1.74Vrms). This echo value is measured under a variety of conditions: with loopback enabled (line input disconnected); with loopback disabled under all receiver gain ranges; and with the line shorted (S1 closed in Figure 4). POWER DISSIPATION Approximately 75% of the power dissipation in the AFE1103 is in the analog circuitry, and this component does not change with clock frequency. However, the power dissipa- tion in the digital circuitry does decrease with lower clock frequency. In addition, the power dissipation in the digital section is decreased when operating from a smaller supply voltage, such as 3.3V. (The analog supply, AVDD, must remain in the range 4.75V to 5.25V.) The power dissipation listed in the specifications section applies under these normal operating conditions: 5V Analog Power Supply; 3.3V Digital Power Supply; standard 13.5dBm delivered to the line; and a pseudo-random equiprobable sequence of HDSL output pulses. The power dissipation specifications includes all power dissipated in the AFE1103, it does not include power dissipated in the external load. The external power is 16.5dBm, 13.5dBm to the line and 13.5dBm to the impedance matching resistors. The external load power of 16.5dBm is 45mW. The typical power dissi- pation in the AFE1103 under various conditions is shown in Table I. FIGURE 4. Uncancelled Echo Test Diagram. TYPICAL POWER BIT RATE DISSIPATION PER AFE1103 DVDD IN THE AFE1103 (Symbols/sec) (V) (mW) 584 (E1) 3.3 250 584 (E1) 5 300 392 (T1) 3.3 240 392 (T1) 5 270 146 (E1/4) 3.3 230 146 (E1/4) 5 245 TABLE I. Typical Power Dissipation. rxHYB N AFE1103 rxLINE P rxLINE N REF N rxD13 - rxD0 rxHYB P txLINE N txLINE P txDAT P 100pF 0.01µF 576 Ω 1.54k Ω 13 Ω 13 Ω 5.6 Ω 1:2 5.6 Ω 0.047µF 150 Ω 576 Ω 0.047µF 2k Ω 2k Ω 100pF 750 Ω Transmit Data Uncanceled Echo 0.1µF 750 Ω 0.1µF 2k Ω 2k Ω 135 Ω S 1 |
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