The AMS3144 is a thick-film hybrid circuit comprising a telephoneline interface and tone demodulator for detecting incoming CallingLine Identification tones provided by local telephone companies.It meets the requirements imposed by the FCC for devices connectedto the telephone network.
Features | Pin Functions and Pinouts| Absolute Maximum Ratings
DC Operating Characteristics | AC Operating Characteristics
Application Information |
NAME PIN # DESCRIPTIONLine A.....1.......Tip or Ring side of telephone lineLine B.....3.......Ring or Tip side of telephone lineGND.....9,15,21....GroundL/30......10.......Output signal equal to 1/30 of AC voltage on telephone line -- used to determine presence of ringing voltageV+........12.......Power supply, 5 to 15 voltsDATA......13.......Serial data output (open collector w/ 20K pullup to V+)CARRIER...14.......Low-true output indicating presence of signal (open collector, no internal pullup)
Supply voltage, V+ to GND 0 to +18 voltsDifferential voltage, Line A to Line B ±1000V peak for 1msCommon mode voltage, Line A & Line B to GND 1000VRMS 60Hz for 90s, ±2000V peak for 1msStorage Temperature -55 to 125 °COperating Temperature 0 to 70 °C
Except as specified, V+=5 voltsParam| Description |Notes|Min |Typ |Max |Unit | | | | | | V+ | Supply Voltage | |4.75| |15.5|volts IC | Supply Current | | | 6 | | mA IOL | Sink Current | 1 | 3 | | 5 | mAVL/30| DC offset, L/30 | | | |1.85|voltsRL/30| L/30 load resistance| 2 |10K | | |ohms RID | Input resistance | 3 | |1.2M| |ohms RIC | Input resistance | 4 | |300K| |ohmsNotes:
1. Sink current into DATA or CARRIER pin 2. Load resistance from L/30 to V+ or to GND 3. Differential (Line A to Line B) input resistance 4. Common mode (Line A + Line B to GND) input res.
Characteristic |Min| Typ|Max|Unit|Note | | | | |Mark (logical 1) frequency | |1200| | Hz |Space (logical 0) frequency | |2200| | Hz |Transmission rate | |1200| |baud|Detection threshold | | |-30|dBm | 1CARRIER detect/release delay | | 2 | | ms | 2Metallic to longitudinal bal.| 60| | | dB | 360Hz common mode tolerance | 30| | |VRMS|4,5 |120| | |VRMS|4,6Notes:
1. 0dBm=0.7746 volts 2. Time from application or removal of signal output at CARRIER pin 3. Per FCC 68.310 4. Level of induced 60Hz common mode voltage on telephone line at which part will continue to function 5. With +5 volt supply 6. With +15 volt supply
Caller Identification signaling is transmitted by the centraloffice during the interval between the first and second burstsof ringing when there is an incoming call. The data are precededby a 250ms "channel seizure" signal and a 150ms "conditioning"signal (see figure 1), both of which will cause an output on theCARRIER pin of the AMS3144.
The channel seizure signal consists of an alternating patternof 1s and 0s; it is followed by 150ms of logical 1 (1200Hz carrier)which constitutes the conditioning signal, one word each indicatingmessage type and length, and the data. At the conclusion of thedata there is a check-sum word, being the 2s complement of themodulo 256 sum of the previous words. Each word is preceded bya start bit (logical 0) and succeeded by a stop bit (logical 1);the least significant bit is transmitted first.
Figure 2 illustrates a typical application. The AMS3144 is coupledto the line through 0.1µF ±10% capacitors; these musthave a DC working voltage of 200 volts or greater. Ringing isdetected at the output of a comparator connected to the L/30 outputof the hybrid. The comparator generates a square wave which followsincoming ringing; the microcontroller can qualify the ringingfor frequency and duration to avoid false detection of line noises.
It is not strictly necessary to use ringing detection to alertthe system that identification data will follow. Figure 3 isa minimum component count application in which the CARRIER outputof the hybrid wakes up the controller. Various tones and evenspeech on the line will cause a CARRIER output from time to time,but the firmware can be smart enough to distinguish between validCaller ID data and junk.
Figure 4 shows a battery powered application. It uses a micropowerregulator to supply the hybrid, normally shut down except whenthe controller tells it to turn on (usually for four seconds afterthe end of the first ringing burst, or until after all valid datahave been collected). With the hybrid normally unpowered, theoptocoupler circuit must be used to detect ringing and wake upthe controller.
There is no handshaking capability to the transmission methodused for Caller ID; if there is an error in the incoming datathere is no provision for recovery. Given that we look for CallerID data at the end of a lengthy, noisy, and unterminated twistedpair, it is not unusual for several percent of incoming transmissionsto fail the check-sum test. Proper implementation of hardwareand intelligent design of software can minimize these failures.
The common mode tolerance of the AMS3144 (that is, the amountof noise on the phone line that it can withstand and still operate)is a function of supply voltage -- see AC Operating Characteristicstable. While a 5 volt supply will be adequate for the majorityof phone lines, some are so noisy that a 12- or 15-volt supplywill make the difference between hardly working at all and havinga very low error rate. A good rule of thumb is: if you have +12or +15 volts available, use it. (Figure 5 shows how to shiftthe output of the AMS3144 operating at higher supply voltage tostandard five volt logic levels.)
Smart software design can also help. For example, most of thedata received are ASCII numerals, and all ASCII numerals takethe binary form 0011xxxx. By forcing the two most significantbits of words you know should be numerals to 00 (as by ANDingwith 00111111) and by forcing the next two bits to be 11 (as byORing with 00110000), you can eliminate a substantial percentageof errors.
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