ISO2-CMOS MT8840 Data Over Voice Modem Features ISSUE 4 Ordering Information • Performs ASK (amplitude shift keyed) modulation and demodulation • 32 kHz carrier frequency • Up to 2 kbit/s full duplex data transfer rate • On-chip oscillator • On-chip tone caller for alerting functions • Adjustable tone caller frequencies • Selectable self-loop test mode • 5V/2.5mA power supply • ISO2 -CMOS and switched capacitor technologies • 18 Pin DIP MT8840AE MT8840AS • Simultaneous data and voice communication in PABXs • 2 kbit/s data modem • "Smart" telephone sets OSC2 The MT8840 is a carrier over voice modem which allows simultaneous transfer of voice and data over a single pair of wires. Data is transferred on an amplitude shift keyed (ASK) 32 kHz carrier. On-chip filters remove voice frequency signals from the received composite voice and data signal prior to demodulation. The modulating signal is a bit stream with a typical data rate of 2 kbit/s. In addition, the device contains a two tone warbler which functions as a telephone ringer. The device is fabricated in MITEL’s double-poly ISO2-CMOS technology utilizing switched-capacitor techniques. ETC MTC FATC CK32 Timing and Control TxDI RxDO DET CRx Tone Caller TX PostFilter TX Bandpass Filter Modulator Demodulator 18 Pin Plastic DIP 18 Pin SOIC 0°C to +85°C Description Applications OSC1 November 1990 RX Bandpass Filter AGC VDD VSS RX PreFilter VRef TCO R O U T I N G TxO RxE RxI LOOP Figure 1 - Functional Block Diagram 5-3 MT8840 ISO2-CMOS DET CRx Rxl RxE LOOP VRef TxO TxDI VSS 1 2 3 4 5 6 7 8 9 18 17 16 15 14 13 12 11 10 VDD RxDO OSC2 OSC1 CK32 ETC MTC TCO FATC 18 PIN PLASTIC DIP/SOIC Figure 2 - Pin Connections Pin Description 5-4 Pin # Name Description 1 DET Demodulator detection level adjust input (Analog). Internal resistor divider applies 2.36V in open circuit condition. Connection of external resistor will vary detect level. 2 CRx External AGC time constant adjust input (Analog). Connect external capacitor to VSS. 3 RxI Modulated receive signal input (Analog). Biased at VRef. 4 RxE Receive enable input (Digital) with internal pull up. Active high. 5 LOOP 6 VRef Internal reference supply voltage input (Analog) . 7 TxO Modulated transmit carrier output (Analog). 8 TxDI Transmit data input (Digital). 9 VSS Negative power supply. 10 FATC Tone caller center frequency adjust input (Analog). 11 TCO Tone caller output (Digital). 12 MTC Mute tone caller input (Digital) with internal pull down. Active high. 13 ETC Enable tone caller input (Digital) with internal pull down. Active high. 14 CK32 32 kHz data strobe output (Digital). 15 OSC1 Clock Input 16 OSC2 Clock Output to drive external devices. 17 RxDO Receive data output (Digital). Synchronized to CK32. 18 VDD Self-test mode select input (Digital) with internal pull down. Active high. Positive power supply. 3.579545 MHz crystal connected between these pins completes internal oscillator. ISO2-CMOS MT8840 Functional Description Applications The MT8840 contains the modulator and demodulator circuitry for 32 kHz ASK signalling as well as a two-tone warbler (tone caller) to replace the function of the mechanical telephone ringer. Figures 3 through 5 show how the MT8840 may be utilized to transfer data and voice simultaneously over a single pair of wires in digital or analog PABXs and "smart" telephone sets. In all three figures a microprocessor sends/receives data to/from the MT8840 via a UART which converts the data format from parallel-to-serial or serial-to-parallel for the transmit and receive directions, respectively. In the receive direction the MT8840 has on-board filters to reject voice-band signals leaving only the 32 kHz carrier. This carrier is then demodulated to recover the received data. In the transmit direction the data to be sent is modulated and passed on to a summing circuit which sums the modulated 32 kHz carrier and voiceband signals for transmission over the telephone line. In the PABX the Filter/Codec has filters which reject the 32 kHz carrier from the received composite voice and data signal allowing only voiceband signals to pass through which are then PCM encoded for digital switching. However, in both the analog PABX and smart telephone set, lowpass filters could be included to bandlimit the received signal leaving only voice signals to be passed on to the switch array or handset earpiece. A 32 kHz carrier is 100% amplitude modulated by the digital bit stream applied to input TxDI. This results in an amplitude shift keyed (ASK) 32 kHz carrier. A logical high at TxDI disables the carrier and a logical low enables it. The digitally modulated waveform is shaped by the Tx BANDPASS FILTER and smoothed by the Tx POST FILTER. The signal then enters the routing block where it is transferred to the TxO output. The modulated 32 kHz receive signal is applied to RxI. With a logical low applied to LOOP and a logical high applied to RxE, receive signals are routed to the Rx PREFILTER. High frequencies are removed by the Rx PREFILTER to prevent aliasing in the switched capacitor Rx BANDPASS FILTER. Voice signals are removed by the bandpass filter which is followed by an AGC circuit. This provides a dynamic range of 20dB for the receiver. An external 1µF capacitor connected from CRx to VSS is required to control the AGC attack and decay time constants. Data is recovered from the received signal in the demodulator. The minimum voltage level to which the demodulator responds may be adjusted by connecting a resistor from DET to V DD or VRef. Since DET is the input to a comparator, noise should be kept to a minimum at this pin. The recovered receive data is synchronized to the leading edge of the 32 kHz clock (available at CK32) before appearing at RxDO. When in loop around mode, the Rx PREFILTER input is internally disconnected from the RxI input pin and connected to TxO. The transmitter output is still available at TxO. A two tone warbling audio signal is available at TCO when the tone caller enable input (ETC) is high. TCO is internally clamped to VRef when the tone caller is disabled. The tone output can be attenuated by 20dB if a logical high is applied to the tone caller mute input (MTC). 5-5 MT8840 ISO2-CMOS Tx Data Microprocessor UART Rx Data Tx MT8840 Rx Summing Circuit 2W/4W Converter PCM Highway Tx Telephone line FILTER/ CODEC (MT896X) Rx Figure 3 - Digital PABX Block Diagram Tx Data Microprocessor UART Tx MT8840 Rx Data Rx Summing Circuit (Optional) To Another Telephone Extension SLIC Analog Switch Array (MT8804) LowPass Filter Rx Tx Figure 4 - Analog PABX Block Diagram 5-6 2W/4W Converter Telephone line ISO2-CMOS Tx Data Tx MT8840 Summing Circuit Telephone line MT8840 Rx Microprocessor UART Rx Data 2W/4W Converter Handset LowPass Filter (Optional) Figure 5 - Smart Telephone Set Block Diagram VDD OSC1 MT8840 OSC2 C=33pF MT8840 OSC1 MT8840 OSC1 OSC2 OSC2 C=1000pF ••• C=1000pF VSS When a single crystal is shared among a number of MT8840 devices, OSC1 and OSC2 should be a.c. coupled with a 1000 pF capacitor as shown above. This capacitor is not needed between the device with the crystal and the first driven device. A capacitor should be used in the first stage whenever such a chain of devices is driven from a clock instead of a crystal. A 33pF capacitor should be connected between OSC1 and VSS to compensate for the load on OSC2. Figure 6 - Crystal Oscillator Connections for Driving Multiple MT8840s 5-7 MT8840 ISO2-CMOS Absolute Maximum Ratings* Parameter Symbol Min Max Unit VDD-VSS -0.3 +7.0 V VSS-0.3 VDD+0.3 V 20 mA +150 °C 850 mW 1 Supply Voltage 2 Voltage On Any Pin VMax 3 Current On Any Pin IMax 4 Storage Temperature 5 Package Power Dissipation TS -65 PDiss * Exceeding these ratings may cause permanent damage. Functional operation under these conditions is not implied. Recommended Operating Conditions Parameter 1 Operating Supply Voltages 2 3 Operating Supply Currents 4 Symbol Min Typ Max Unit VDD 4.75 5 5.25 V VRef 0.4VDD IDD 2.5 IRef 5 Operating Temperature TO 6 Load Capacitance (TxO) CL 7 Load Resistance (TxO) RL D.C. Characteristics - VDD = 5.0 V ± 5% 2 3 4 5 6 D I G I T A L 7 8 9 Sym 19 20 21 KΩ Min Typ Max Unit ±10 µA Test Conditions VIH 3.5 5.0 V Output Low Voltage V OL 0.4 V IOL = 0.4mA Output High Voltage VOH 4.6 V IOH = 0.4mA I OL 0.4 mA VOL = 0.4V 0.1 mA 0.4 mA 0.1 mA VIN = 0 to VDD Output Drive Current OSC2 P Channel Source (Except OSC2) IOH RIN I / O 10 Input High Voltage Input Resistance (FATC) 18 pF V 12 17 50 1.5 IIN 16 °C 0 Input Current (RxI, FATC) 15 +85 VIL 11 14 µA Input Low Voltage OSC2 A N A L O G 200 IIN 10 13 mA Input Current N Channel Sink (Except OSC2) I / O 5.0 VSS =0V T = 0 - 85oC (All voltages are referenced to VSS /GND) Characteristics 1 0 V ±10 500 µA 170 KΩ (DET to VRef) 23 KΩ 50 pF (FATC) 10 pF Any Digital Input 5.0 CIN VIN = 0 to 5.0V KΩ (DET to VDD) Input Capacitance (RxI) VOH = 4.6V 7.5 pF 100 Ω (TCO) 3 KΩ MTC = 0 (TCO) 30 KΩ MTC = 1 Output Resistance (TxO) Output Offset Voltage (TxO) RO VO ±25 ±200 mV 22 Output Voltage (DET) VO 2.20 2.36 2.55 V See Note Notes: 1. Voltage specified is generated internally and measured with no external components connected to DET 5-8 1 ISO2-CMOS A.C. Characteristics - VDD=5.0V±5% Characteristics 1 Crystal/Clock Frequency 2 Clock Input (OSC 1) 3 4 5 6 7 8 9 Rise Time Fall Time D I Duty Cycle G Clock Output (OSC 2) I Rise Time T A Fall Time L Duty Cycle 10 Capacitive Load I / Clock Output (CK32) 12 O Rise Time 11 V SS=0V T=0 - 85°C (All voltages are referenced to VSS/GND) Sym fC Min Typ Max 3.5759 3.5795 3.5831 Unit MHz tLHCI 100 ns tHLCI 100 ns 60 % DCCI 40 50 CL = 30pF, 3.58MHz ext. tHLCO 100 ns clock to OSC1 DCCO 50 CLCO FC32 32508 32541 % 30 pF 32574 Hz fc = 3.5795MHz tLH32 100 ns 10% - 90% of (VDD - VSS) CL = 100pF tHL32 100 ns Duty Cycle DC32 50 % 15 Capacitive Load CL32 Low Tone Frequency T O 19 N High Tone Frequency 20 E fW fLT 18 21 Harmonic Relationship C 22 A Warbler Output (TCO) 23 L Rise Time L 24 Fall Time E 25 Duty Cycle R 26 Output Level (TCO) fHT 7.935 29 30 31 32 33 34 35 Modulated Frequency M O Output Level (TxO) D Output Level (TxO) U variation vs. VDD L A Transmit Data Input (TxDI) Rise Time T O Fall Time R Data Rate (TxDI) 36 D 37 E M 38 O 39 D U 40 L 41 A T 42 O 43 R Notes: Input Impedance (RxI) 7.945 pF 7.955 Hz fc = 3.5795MHz ± 0.1% 352 390 428 Hz FATC = 0, fc= 3.5795MHz 1148 1260 Hz FATC = VDD, fc= 3.5795MHz 440 487 535 Hz FATC = 0, fc= 3.5795MHz 1295 1434 1574 Hz FATC = VDD, fc= 3.5795MHz 100KΩ load to VRef CL = 30pF, MTC = 0 fHT/fLT 1.25 tLHWO 500 ns tHLWO 500 ns DCWO 50 % VTCC VDD Vpp MTC = 0 0.625 Vpp MTC = 1 (100KΩ load to VRef) 32541 Hz fMOD VTxO 225 VTxO 250 270 100 mVpp VDD = 5V % tLHTxDI 100 ns tHLTxDI 100 ns fData 2 ZIN 50 Valid Input Level - Data (RxI) VRxI Valid Input Level - Data + Voice VRxI Receive Data Output (RxDO) fData 40 k/bits See Note 1 KΩ 400 3.0 32 kHz Input Frequency mVpp See Note 2 Vpp 2 kbit/s Rise Time 100 ns 10% - 90% of (VDD - VSS) Fall Time 100 ns CL = 100pF Capacitive Load Duty Cycle 1. 2. 100 1036 27 28 10% - 90% of (VDD - VSS) ns Fall Time 17 OSC1, OSC2 100 14 Warbler Frequency (TCO) Test Conditions tLHCO 13 16 MT8840 40 50 100 pF 60 % All A.C. parameters are based on a typical data rate of 2 kbit/s. Measured with no external resistor to DET input. Detection level internally set to 2.36V typical. 5-9 MT8840 ISO2-CMOS A.C. Characteristics (Continued) Characteristics 44 45 46 47 Notes: 5-10 D E M O D 1. 2. Sym Min Typ Max Unit Test Conditions Inband Noise Rejection (S/N) 12 dB Input Sig. (RxI) = 400mVpp Attenuation to Voice Signals 40 dB fin = 0 - 5KHz Detect Filter Q Detector Center Frequency Q 3.8 32 kHz All A.C. parameters are based on a typical data rate of 2 kbit/s. Measured with no external resistor to DET input. Detection level internally set to 2.36V typical.