MITEL MT8840

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.