Datasheet MT8840AE, MT8840AS Datasheet (MITEL)

ISO2-CMOS



Data Over Voice Modem

MT8840

Features

• Performs ASK (amplitude shift keyed)
modulat ion an d dem odula tion

• 32 kHz carrier f reque ncy

• Up to 2 kbit/s full duplex data transfer rate

• On-chip oscillator

• On-chip tone caller for alerting functions

• Adjustab le to ne call er fre quenc ies

• Selectab le self-l oop tes t mod e

• 5V/2.5mA power supply

2

•ISO

-CMOS and switch ed capa cito r

technologies

•18 Pin DIP

Applications

• Simultaneous data and voice communication in
PABXs

• 2 kbit/s data modem

• "Smart" t eleph one set s

ISSUE 4 November 1990

Ordering Information

MT8840AE 18 Pin Plastic D IP
MT8840AS 18 Pin SOIC

0°C to +85°C

Descript io n

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
utilizing switched-capacitor techniques.

2

-CMOS technology

TxDI

RxDO

OSC1 OSC2

Modulator

Demodulator

DET CRx V

Figure 1 - Functional Block Diagram

AGC

CK32

Timing

and

Control

TX Bandpass

RX Bandpass

DD

Filter

Filter

V

SS

ETC

MTC FATC

Tone

Caller

TX Post-

Filter

RX Pre-

Filter

V

Ref

R
O
U
T

I
N
G

LOOP

TCO

TxO

RxE

RxI

5-3

MT8840 ISO

2

-CMOS

DET
CRx

RxE

LOOP

VRef

TxO

TxDI

VSS

1
2

3

Rxl

4
5

6
7
8
9

18 PIN PLASTIC DIP/SOIC

18
17
16
15
14
13
12
11
10

VDD
RxDO
OSC2
OSC1
CK32
ETC
MTC
TCO
FATC

Figure 2 - Pin Connections

Pin Description

Pin # Name Descripti on

1 DET Demodulat or detect ion level adj ust input (Ana log). Internal resistor divider applie s

2.36V in open circuit condition. Connect ion of external resistor will vary detect level.
2 CRx E xtern al AGC time constant adjust input (Analog). Connect external capacitor to V
3 RxI Modulated receive signal input (Analog). Biased at V
4 R xE Receive enable inpu t (Digital) wit h inte rnal pull up. Active high.
5 LOOP Self-test mode select input (Digit al) with interna l pull down. Active high.
6V

Ref

Internal reference supply voltage inp ut (Analog) .
7 TxO Modulate d transmit carrier output (Analog).
8 TxDI Transmit data input (Digital).
9V

SS

Negative power supply.

10 FATC Tone caller center frequency adjust inpu t (Analog).
11 TCO Tone caller output (Digital).
12 MTC Mute tone caller input (Digital) with internal pull down. Active high.
13 ETC Enab le tone caller in put (Digital ) with int ernal pull down. Active high.
14 CK32 32 kHz data strobe output (Digital).
15 OSC1 Clock Input 3.579545 MHz crystal connected between
16 OSC2 Clock Output to drive external devices.

these pins complete s internal oscillato r.

17 RxDO Receive data output (Digital). Synchronize d to CK32.
18 V

DD

Positive power supply.

Ref

.

SS

.

5-4

ISO

2

-CMOS MT8840

Functional Description

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
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 VDD or V
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.

is required to

SS

. Since

Ref

Applications

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 o n to th e s wi tch a r ra y or h a ndset earpiece.

When in loop around mode, the Rx PREFILTER
input is internally disconnect ed 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
disabled. The tone output can be attenuated by 20dB
if a logical high is applied to the tone caller mute
input (MTC ).

when the tone caller is

Ref

5-5

MT8840 ISO

2

-CMOS

Micro-

processor

Micro-

processor

PCM

Highway

UART

UART

Tx Data

Rx Data

FILTER/
CODEC

(MT896X)

MT8840

Tx

Rx

Tx

Rx

Summing

Circuit

Figure 3 - Digital PABX Block Diagram

Tx Data

Rx Data

MT8840

Rx

Tx

Summing

Circuit

2W/4W

Converter

Telephone

line

To

Another

Telephone

Extension

SLIC

Analog

Switch

Array

(MT8804)

(Optional)

Low­Pass
Filter

Tx

Rx

Figure 4 - Analog PABX Block Diagram

2W/4W

Converter

Telephone

line

5-6

ISO

2

-CMOS MT8840

V

DD

Telephone

line

2W/4W

Converter

Tx Data

UART

Rx Data

Summing

Circuit

Tx

MT8840

Rx

Low­Pass
Filter

(Optional)

Figure 5 - Smart Telephone Set Block Diagram

Micro-

processor

Handset

OSC1

MT8840

OSC2

V

SS

When a si ng le cry s tal is shared am on g a nu mb er o f M T8 84 0 devices, OSC1 an d O SC 2 sh ou ld be a.c . c oupled with a 100 0
pF capac ito r a s sh own a bo ve . This capacito r is n ot ne ed ed b etween the dev ic e with the cryst al an d th e f ir s t d riv en d ev ic e .
A capacitor should be used in th e fi r st sta ge when ev e r su ch a chain of devices is driv en from a c lo c k ins te ad of a c ry sta l. A
33pF capacitor should be connected between OSC1 and VSS to compensate for the load on OSC2.

C=33pF

MT8840

OSC1

OSC2

C=1000pF

OSC1

MT8840

OSC2

C=1000pF

Figure 6 - Crystal Oscillator Connections for Driving Multiple MT8840s

• • •

5-7

MT8840 ISO

2

-CMOS

Absolute Maximum Ratings*

Parameter Symbol Min Max Unit

1 Supply Voltage V
2 Voltage On Any Pin V
3 Current On Any Pin I
4 Storage Temperature T
5 Package Power Dissipation P

* Exceeding these ratings may cause permanent damage. Functional operation under these conditions is not implied.

DD-VSS

Max

Max

S

Diss

-0.3 +7.0 V

VSS-0.3 VDD+0.3 V

20 mA

-65 +150 °C
850 mW

Recommended Operating Conditions

Parameter Symbol Min Typ Max Unit

1 Operating Supply Voltages V
2V
3 Operating Supply Current s I
4I
5 Operating Temperatu re T
6 Load Capacitance (TxO) C
7 Load Resistance (TxO) R

D.C. Characteristics - V

= 5.0 V ± 5% VSS =0V T = 0 - 85oC (All voltages are referenced to VSS /GND)

DD

DD
Ref

DD

Ref

O

L
L

Characteristics Sym Min Typ Max Unit Test Conditions

4.7555.25V

0.4V

DD

V

2.5 5.0 mA
200 µA

0+85°C

50 pF

10 KΩ

1
2 Input Low Voltage V
3 Input High Voltage V
4 Output Low Voltage V
5 Output Hi g h Voltage V
6 Output Drive Current
7 N Channel Sink (Except OSC2) I
8OSC2 0.1 mA
9 P Channel Source (Except OSC2) I

Input Current I

D

I

G

I

T

A

L

I
/

O

IN

IH

OL

OH

OL

OH

±10 µA VIN = 0 to V

IL

0 1.5 V

3.5 5.0 V

0.4 V IOL = 0.4mA

4.6 V IOH = 0.4mA

0.4 mA VOL = 0.4V

0.4 mA VOH = 4.6V
10 OSC2 0.1 mA
11
12 Input Resistance (FATC) R
13 (DET to V
14 (DET to V
15 Input Capacitance ( R xI) C
16 (FATC) 10 pF
17 Any Digital Inp ut 5.0 7.5 pF
18 Output Resistance (Tx O) R
19 (TCO) 3 KΩ MTC = 0
20 (TCO) 30 KΩ MTC = 1
21 Output Offset Voltage (TxO) V
22 Output Voltage (DET) V

Notes: 1. Voltage specified i s ge ne rated internall y and measured with no externa l c o mp onents connec ted to DET

Input Current (RxI, FATC) I

) 170 KΩ

A
N
A

DD

)23KΩ

Ref

L
O
G

I
/

O

IN

500 KΩ

IN

IN

O

O

2.20 2.36 2.55 V See Not e 1

O

50 pF

100 Ω

±25 ±200 mV

±10 µA VIN = 0 to 5.0V

DD

5-8

ISO

2

-CMOS MT8840

A.C. Characteristics - V

=5.0V±5% VSS=0V T=0 - 85°C (All voltages are referenced to VSS/GND)

DD

Characteristics Sym Min Typ Max Uni t Tes t Con ditions

1

Crystal/Clock Frequency f

3.5759 3.5795 3.5831 MHz OSC1, OSC2

C

2 Clock Input (OSC 1)
3 Rise Time t
4 Fall Time t

D

I

5 Duty Cycle DC

G

6 Clock Output (OSC 2)

I

7 Rise Time t

T
A

8 Fall Time t

L

9 Duty Cycle DC

10 Capacitive Load C

I

11 Clock Output (CK32) F

/

O

12 Rise Time t
13 Fa ll Time t
14 Duty Cycle DC
15 Capacitive Load C
16

Warbler Frequency (TCO) f

17 Low Tone Frequency f

T

18 1036 1148 1260 Hz FATC = V

O

19 High Tone Frequency f

N

E

20 1295 1434 1574 Hz FATC = V
21 Harmonic Relationship f

C

22 Warbler Output (TCO)

A

23 Rise Time t

L
L

24 Fa ll Time t

E

25 Duty Cycle DC

R

26 Output Level (TCO) V

LHCI
HLCI

CI

LHCO
HLCO

CO
LCO
C32

LH32
HL32

32
L32
W
LT

HT

HT/fLT

LHWO

HLWO

WO

TCC

40 50 60 %

100 ns CL = 30pF, 3.58MHz ext.
100 ns clock to OSC1

50 %

32508 32541 32574 Hz fc = 3.5795MHz

100 ns 10% - 90% of (VDD - VSS)
100 ns CL = 100pF

50 %

7.935 7.945 7.955 Hz fc = 3.5795MHz ± 0.1%
352 390 428 Hz FATC = 0, fc= 3.5795MHz

440 487 535 Hz FATC = 0, fc= 3.5795MHz

1.25

500 ns 100KΩ load t o V
500 ns CL = 30pF, MTC = 0

50 %

V

DD

27 0.625 V
28
29 Output Level (TxO) V
30 Output Level (TxO)
31 variation vs. V
32 Transmit Data Input (TxDI)
33 Rise Time t
34 Fa ll Time t
35 Data Rate (TxDI) f
36
37 Vali d Input Level - Data (RxI) V
38 Vali d Input Level - Data + Voice V
39 Receive Data Output (RxDO) f
40 Rise Time 100 ns 1 0 % - 90% of (V
41 Fa ll Time 100 ns C
42 Capacitive Load 100 pF
43 Duty Cycle 40 50 60 %

Notes: 1. All A.C . p a r ameters are base d on a typical data rate of 2 k bi t/s .

Modulated Freque ncy f

M
O

MOD

TxO

225 250 270 mVppVDD = 5V

32541 Hz

D
U

L

DD

V

TxO

100 %

A

T
O
R

Input Impedance (RxI) Z

D

E
M
O

D
U

LHTxDI
HLTxDI

Data

IN
RxI
RxI

Data

2 k/bits See Note 1

50 KΩ 32 kHz Input Frequency

40 400 mVppSee Note 2

2 kbit/s

L
A

T
O
R

2. Measure d w ith n o e xt ern al r e sist or to D ET i np ut . D e te ct ion l ev el in te rna ll y se t t o 2 .3 6V typical.

100 ns 10% - 90% of (VDD - VSS)
100 ns

30 pF

100 pF

, fc= 3.5795MHz

DD

, fc= 3.5795MHz

DD

V

MTC = 0

pp

MTC = 1 (100KΩ load to V

pp

100 ns
100 ns

3.0 V

pp

= 100pF

L

Ref

DD

Ref

- VSS)

)

5-9

MT8840 ISO

2

-CMOS

A.C. Characteristics (Continued)

Characteristics Sym Min Typ Max Unit Test Conditions

44
45 Attenuation to Voice Signals 40 dB fin = 0 - 5KHz
46 Detect Filter Q Q 3.8
47 Detector C enter Frequency 32 kHz

Notes: 1. All A.C . p arameters are ba se d on a typical data rate of 2 kbi t/s .

Inband Noise Rejection (S/N) 12 dB Input Sig. (RxI) = 400mV

D
E
M
O
D

2. Measure d with no extern al re si st or to DET input. De te ct ion l ev el in te rna ll y se t t o 2 .3 6V typical.

pp

5-10