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TP3057 Datasheet(PDF) 4 Page - National Semiconductor (TI) |
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TP3057 Datasheet(HTML) 4 Page - National Semiconductor (TI) |
4 / 16 page Functional Description (Continued) TRANSMIT SECTION The transmit section input is an operational amplifier with provision for gain adjustment using two external resistors see Figure 4 The low noise and wide bandwidth allow gains in excess of 20 dB across the audio passband to be real- ized The op amp drives a unity-gain filter consisting of RC active pre-filter followed by an eighth order switched-ca- pacitor bandpass filter clocked at 256 kHz The output of this filter directly drives the encoder sample-and-hold circuit The AD is of companding type according to m-law (TP3054) or A-law (TP3057) coding conventions A preci- sion voltage reference is trimmed in manufacturing to pro- vide an input overload (tMAX) of nominally 25V peak (see table of Transmission Characteristics) The FSX frame sync pulse controls the sampling of the filter output and then the successive-approximation encoding cycle begins The 8-bit code is then loaded into a buffer and shifted out through DX at the next FSX pulse The total encoding delay will be ap- proximately 165 ms (due to the transmit filter) plus 125 ms (due to encoding delay) which totals 290 ms Any offset voltage due to the filters or comparator is cancelled by sign bit integration RECEIVE SECTION The receive section consists of an expanding DAC which drives a fifth order switched-capacitor low pass filter clocked at 256 kHz The decoder is A-law (TP3057) or m -law (TP3054) and the 5th order low pass filter corrects for the sin xx attenuation due to the 8 kHz samplehold The filter is then followed by a 2nd order RC active post-filter power amplifer capable of driving a 600X load to a level of 72 dBm The receive section is unity-gain Upon the occur- rence of FSR the data at the DR input is clocked in on the falling edge of the next eight BCLKR (BCLKX) periods At the end of the decoder time slot the decoding cycle begins and 10 ms later the decoder DAC output is updated The total decoder delay is E 10 ms (decoder update) plus 110 ms (filter delay) plus 625 ms( frame) which gives approximately 180 ms 4 |
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Similar Description - TP3057 |
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