MT8840 MITEL | Alldatasheet
Document overview
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Technical content
Features
- 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
- I S O 2-CMOS and switched capacitor technologies
- 1 8 P i n D I P
Applications
- Simultaneous data and voice communication in PABXs
- 2 kbit/s data modem
- "Smart" telephone sets
Description
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 ISO 2-CMOS technology utilizing switched-capacitor techniques.
Ordering Information
MT8840AE 18 Pin Plastic DIP MT8840AS 18 Pin SOIC 0°C to +85°C Figure 1 - Functional Block Diagram OSC1 OSC2 CK32 ETC MTC FATC TxDI RxDO DET CRx V DD VSS VRef LOOP TCO TxO RxE RxI Timing and Control To ne Caller Modulator TX Bandpass Filter TX Post- Filter RX Pre- Filter R O U T I NAGC G RX Bandpass FilterDemodulator ISSUE 4 November 1990 ISO2-CMOS
Figure 2 - Pin Connections Pin Description 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 V Ref. 4 RxE Receive enable input (Digital) with internal pull up. Active high. 5 LOOP Self-test mode select input (Digital) with internal pull down. Active high. Ref Internal reference supply voltage input (Analog) . 7 TxO Modulated transmit carrier output (Analog). 8 TxDI Transmit data input (Digital). SS 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 3.579545 MHz crystal connected between these pins completes internal oscillator.16 OSC2 Clock Output to drive external d evices. 17 RxDO Receive data output (Digital). Synchronized to CK32. 18 V DD Positive power supply. 9 10 DET CRx Rxl RxE LOOP VRef TxO TxDI VSS VDD RxDO OSC2 OSC1 CK32 ETC MTC TCO FATC
18 PIN PLASTIC DIP/SOIC
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. 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 V SS 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 V Ref 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). 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.
- Exceeding these ratings may cause permanent damage. Functional operation under these conditions is not implied. Notes: 1. Voltage specified is generated internally and measured with no external components connected to DET Absolute Maximum Ratings* Parameter Symbol Min Max Unit 1 Supply Voltage V DD -VSS -0.3 +7.0 V 2 Voltage On Any Pin V Max VSS -0.3 V DD +0.3 V
3 Current On Any Pin I Max 20 mA
4 Storage Temperature T S -65 +150 °C
5 Package Power Dissipation P Diss 850 mW
Recommended Operating Conditions Parameter Symbol Min Typ Max Unit 1 Operating Supply Voltages V DD 4 . 7 555 . 2 5 V 2V Ref 0.4VDD V 3 Operating Supply Currents I DD 2.5 5.0 mA 4I Ref 200 µA
5 Operating Temperature T O 0+ 8 5 ° C
6 Load Capacitance (TxO) C L 50 pF
7 Load Resistance (TxO) R L 10 K Ω
D.C. Characteristics - V DD = 5.0 V ± 5% VSS =0V T = 0 - 85oC (All voltages are referenced to VSS /GND) Characteristics Sym Min Typ Max Unit Test Conditions D I G I T A L I O Input Current I IN ±10 µA V IN = 0 to VDD 2 Input Low Voltage V IL 0 1.5 V 3 Input High Voltage V IH 3.5 5.0 V 4 Output Low Voltage V OL 0.4 V I OL = 0.4mA 5 Output High Voltage V OH 4.6 V I OH = 0.4mA
6 Output Drive Current
7 N Channel Sink (Except OSC2) I
OL 0.4 mA V OL = 0.4V 8O S C 2 0 . 1 m A 9 P Channel Source (Except OSC2) I OH 0.4 mA V OH = 4.6V 10 OSC2 0.1 mA A N A L O G I O Input Current (RxI, FATC) I IN ±10 µA V IN = 0 to 5.0V
12 Input Resistance (FATC) R IN 500 K Ω
13 (DET to V DD ) 170 K Ω 14 (DET to V Ref)2 3 K Ω
15 Input Capacitance (RxI) C IN 50 pF
16 (FATC) 10 pF 17 Any Digital Input 5.0 7.5 pF
18 Output Resistance (TxO) R O 100 Ω
19 (TCO) 3 K Ω MTC = 0 20 (TCO) 30 K Ω MTC = 1
21 Output Offset Voltage (TxO) V O ±25 ±200 mV
22 Output Voltage (DET) V O 2.20 2.36 2.55 V See Note 1
Notes: 1. All A.C. parameters are based on a typical data rate of 2 kbit/s. 2. Measured with no external resistor to DET input. Detection level internally set to 2.36V typical. A.C. Characteristics - V DD =5.0V±5% VSS =0V T=0 - 85°C (All voltages are referenced to VSS /GND) Characteristics Sym Min Typ Max Unit Test Conditions D I G I T A L I O Crystal/Clock Frequency f C 3.5759 3.5795 3.5831 MHz OSC1, OSC2
2 Clock Input (OSC 1)
3 Rise Time t LHCI 100 ns 10% - 90% of (V DD - VSS )
4 Fall Time t HLCI 100 ns
5 Duty Cycle DC CI 40 50 60 %
6 Clock Output (OSC 2)
7 Rise Time t LHCO 100 ns C L = 30pF, 3.58MHz ext.
8 Fall Time t HLCO 100 ns clock to OSC1
9 Duty Cycle DC CO 50 %
10 Capacitive Load C LCO 30 pF
11 Clock Output (CK32) F C32 32508 32541 32574 Hz fc = 3.5795MHz
12 Rise Time t LH32 100 ns 10% - 90% of (V DD - VSS )
13 Fall Time t HL32 100 ns C L = 100pF
14 Duty Cycle DC 32 50 %
15 Capacitive Load C L32 100 pF
T O N E C A L L E R Warbler Frequency (TCO) f 17 Low Tone Frequency f LT 352 390 428 Hz FATC = 0, f c= 3.5795MHz 18 1036 1148 1260 Hz FATC = V DD , fc= 3.5795MHz 19 High Tone Frequency f HT 440 487 535 Hz FATC = 0, f c= 3.5795MHz 20 1295 1434 1574 Hz FATC = V DD , fc= 3.5795MHz 21 Harmonic Relationship f HT /fLT 1.25
22 Warbler Output (TCO)
23 Rise Time t LHWO 500 ns 100K Ω load to VRef
24 Fall Time t HLWO 500 ns C L = 30pF, MTC = 0
25 Duty Cycle DC WO 50 %
26 Output Level (TCO) V TCC VDD Vpp MTC = 0
27 0.625 V pp MTC = 1 (100KΩ load to VRef) 28 M O D U L A T O R Modulated Frequency f MOD 32541 Hz
29 Output Level (TxO) V TxO 225 250 270 mV pp VDD = 5V
30 Output Level (TxO)
31 variation vs. V DD VTxO 100 %
32 Transmit Data Input (TxDI)
33 Rise Time t LHTxDI 100 ns
34 Fall Time t HLTxDI 100 ns
35 Data Rate (TxDI) f Data 2 k/bits See Note 1
E M O D U L A T O R Input Impedance (RxI) Z IN 50 K Ω 32 kHz Input Frequency
37 Valid Input Level - Data (RxI) V RxI 40 400 mV pp See Note 2
38 Valid Input Level - Data + Voice VRxI 3.0 V pp
39 Receive Data Output (RxDO) f Data 2 kbit/s
40 Rise Time 100 ns 10% - 90% of (V DD - VSS )
41 Fall Time 100 ns C L = 100pF
42 Capacitive Load 100 pF
43 Duty Cycle 40 50 60 %
Notes: 1. All A.C. parameters are based on a typical data rate of 2 kbit/s. 2. Measured with no external resistor to DET input. Detection level internally set to 2.36V typical. A.C. Characteristics (Continued) Characteristics Sym Min Typ Max Unit Test Conditions 44 D E M O D Inband Noise Rejection (S/N) 12 dB Input Sig. (RxI) = 400mV pp
45 Attenuation to Voice Signals 40 dB f in = 0 - 5KHz
46 Detect Filter Q Q 3.8