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Features
Low Power Consumption
Adjustable Acquisition and Release Times
Central Office Quality and Performance
Power-down and Inhibit Modes (-02 only)
Inexpensive 3.58 MHz Time Base
Single 5 Volt Power Supply
Dial Tone Suppression
Applications
Telephone switch equipment
Remote data entry
Paging systems
Personal computers
Credit card systems
Pin Configuration
Block Diagram
M-8870
DTMF Receiver
Description
The M-8870 is a full DTMF Receiver that integrates
both bandsplit filter and decoder functions into a single
18-pin DIP or SOIC package. Manufactured using
CMOS process technology, the M-8870 offers low
power consumption (35 mW max) and precise data
handling. Its filter section uses switched capacitor
technology for both the high and low group filters and
for dial tone rejection. Its decoder uses digital counting
techniques to detect and decode all 16 DTMF tone
pairs into a 4-bit code. External component count is
minimized by provision of an on-chip differential input
amplifier, clock generator, and latched tri-state inter-
face bus. Minimal external components required
include a low-cost 3.579545 MHz color burst crystal, a
timing resistor, and a timing capacitor.
The M-8870-02 provides a “power-down” option
which, when enabled, drops consumption to less
than 0.5 mW. The M-8870-02 can also inhibit the
decoding of fourth column digits (see Tone Decoding
table on page 5).
Ordering Information
Part #
M-8870-01
Description
18-pin plastic DIP
M-8870-01SM 18-pin plastic SOIC
M-8870-01SMTR 18-pin plastic SOIC, tape and reel
M-8870-02
18-pin plastic DIP, power-down,
option
M-8870-02SM
18-pin plastic SOIC, power-down,
option
M-8870-02T
18-pin plastic SOIC, power-down
option, tape and reel
DS-M8870-R3
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M-8870
Absolute Maximum Ratings
Parameter
Symbol
Value
Power supply voltage (VDD - VSS) VDD
6.0 V max
Voltage on any pin
VDC VSS -0.3, VDD +0.3
Current on any pin
IDD 10 mA max
Operating temperature
TA -40°C to + 85°C
Storage temperature
TS -65°C to + 150°C
Note:
Exceeding these ratings may cause permanent damage. Functional operation under
these conditions is not implied.
Absolute Maximum Ratings are stress ratings. Stresses in
excess of these ratings can cause permanent damage to
the device. Functional operation of the device at these or
any other conditions beyond those indicated in the opera-
tional sections of this data sheet is not implied. Exposure of
the device to the absolute maximum ratings for an extend-
ed period may degrade the device and effect its reliability.
DC Characteristics
Parameter
Symbol
Min
Typ Max
Operating supply voltage
Operating supply current
Standby supply current (see Note 3)
Power consumption
Low level input voltage
High level input voltage
Input leakage current
Pullup (source) current on OE
Input impedance, signal inputs 1, 2
Steering threshold voltage
Low level output voltage
High level output voltage
Output low (sink) current
Output high (source) current
Output voltage VREF
Output resistance VREF
VDD
IDD
IDDQ
PO
VIL
VIH
IIH/IIL
ISO
RIN
VTSt
VOL
VOH
IOL
IOH
VREF
ROR
4.75
-
-
-
-
3.5
-
-
8
2.2
-
VDD - 0.03
1.0
0.4
2.4
-
-
3.0
-
15
-
-
0.1
6.5
10
-
-
-
2.5
0.8
-
10
5.25
7.0
100
35
1.5
-
-
15.0
-
2.5
0.03
-
-
-
2.7
-
*Typical figures are at 25°C and are for design aid only; not guaranteed and not subject to production testing.
Units
V
mA
µA
mW
V
V
µA
µA
m
V
V
V
mA
mA
V
k
Test Conditions
-
-
PD=VDD
f = 3.579 MHz, VDD = 5.0 V
-
-
VIN = VSS or VDD (see Note 2)
OE = 0 V
@ 1 kHz
-
No load
No load
VOUT = 0.4 V
VOUT = VDD - 0.4 V
No load
-
Operating Characteristics - Gain Setting Amplifier
Parameter
Symbol
Min
Typ Max
Input leakage current
Input resistance
Input offset voltage
Power supply rejection
IN
-
± 100
-
RIN 4
--
VOS - ± 25 -
PSRR
50
--
Common mode rejection
CMRR
55
--
DC open loop voltage gain
Open loop unity gain bandwidth
Output voltage swing
Tolerable capacitive load (GS)
Tolerable resistive load (GS)
Common mode range
AVOL
60
--
fC 1.2 1.5 -
VO 3.5 - -
CL - - 100
RL - - 50
VCM 2.5
--
*Typical figures are at 25°C and are for design aid only; not guaranteed and not subject to production testing.
Notes:
1. All voltages referenced to VSS unless otherwise noted. For typical values, VDD = 5.0V, VSS = 0V, TA = 25°C.
Units
nA
M
mV
dB
dB
dB
MHz
VP-P
pF
k
VP-P
2 www.clare.com
Test Conditions
VSS < VIN < VDD
-
-
1 KHz
-3.0V < VIN < 3.0V
-
-
RL 100 Kto VSS
-
-
No load
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M-8870
Functional Description
M-8870 operating functions (see block diagram on
page 1) include a bandsplit filter that separates the
high and low tones of the received pair, and a digital
decoder that verifies both the frequency and duration
of the received tones before passing the resulting 4-bit
code to the output bus.
Filter
The low and high group tones are separated by apply-
ing the dual-tone signal to the inputs of two 6th order
switched capacitor bandpass filters with bandwidths
that correspond to the bands enclosing the low and
high group tones. The filter also incorporates notches
at 350 and 440 Hz, providing excellent dial tone rejec-
tion. Each filter output is followed by a single-order
switched capacitor section that smooths the signals
prior to limiting. Signal limiting is performed by high-
gain comparators provided with hysteresis to prevent
detection of unwanted low-level signals and noise.
The comparator outputs provide full-rail logic swings
at the frequencies of the incoming tones.
Decoder
The M-8870 decoder uses a digital counting tech-
nique to determine the frequencies of the limited tones
and to verify that they correspond to standard DTMF
frequencies. A complex averaging algorithm is used to
protect against tone simulation by extraneous signals
(such as voice) while tolerating small frequency varia-
tions. The algorithm ensures an optimum combination
of immunity to talkoff and tolerance to interfering sig-
nals (third tones) and noise. When the detector rec-
ognizes the simultaneous presence of two valid tones
(known as signal condition), it raises the Early
Steering flag (ESt). Any subsequent loss of signal
condition will cause ESt to fall.
Basic Steering Circuit
Steering Circuit
Before a decoded tone pair is registered, the receiver
checks for a valid signal duration (referred to as char-
acter-recognition-condition). This check is performed
by an external RC time constant driven by ESt. A logic
high on ESt causes VC (see block diagram on page 1)
to rise as the capacitor discharges. Provided that sig-
nal condition is maintained (ESt remains high) for the
validation period (tGTF), VC reaches the threshold (VTSt)
of the steering logic to register the tone pair, thus latch-
ing its corresponding 4-bit code (see DC
Characteristics on page 2) into the output latch. At this
point, the GT output is activated and drives VC to VDD.
GT continues to drive high as long as ESt remains
high. Finally, after a short delay to allow the output
latch to settle, the delayed steering output flag (StD)
goes high, signaling that a received tone pair has been
registered. The contents of the output latch are made
available on the 4-bit output bus by raising the three-
state control input (OE) to a logic high. The steering
circuit works in reverse to validate the interdigit pause
between signals. Thus, as well as rejecting signals too
short to be considered valid, the receiver will tolerate
signal interruptions (dropouts) too short to be consid-
ered a valid pause. This capability, together with the
ability to select the steering time constants externally,
allows the designer to tailor performance to meet a
wide variety of system requirements.
Single-Ended Input Configuration
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M-8870
Pin Functions
Pin Name
Description
1 IN+ Non-inverting input
Connections to the front-end differential amplifier.
2 IN- Inverting input
3 GS Gain select. Gives access to output of front-end amplifier for connection of feedback resistor.
4 VREF Reference voltage output (nominally VDD/2). May be used to bias the inputs at mid-rail.
5 INH* Inhibits detection of tones representing keys A, B, C, and D.
6 PD* Power down. Logic high powers down the device and inhibits the oscillator. Internal pulldown.
7 OSC1 Clock input
3.579545 MHz crystal connected between these pins completes the internal oscillator.
8 OSC2 Clock output
9 VSS Negative power supply (normally connected to 0 V).
10 OE Tri-statable output enable (input). Logic high enables the outputs Q1 - Q4. Internal pullup.
11-14 Q1, Q2, Tri-statable data outputs. When enabled by OE, provides the code corresponding to the last valid tone pair
Q3, Q4 received (see Tone Decoding table on page 5).
15 StD Delayed steering output. Presents a logic high when a received tone pair has been registered and the output latch is
updated. Returns to logic low when the voltage on St/GT falls below VTSt.
16 ESt Early steering output. Presents a logic high immediately when the digital algorithm detects a recognizable tone pair (signal
condition). Any momentary loss of signal condition will cause ESt to return to a logic low.
17 St/GT Steering input/guard time output (bidirectional). A voltage greater than VTSt detected at St causes the device to register the
detected tone pair and update the output latch. A voltage less than VTSt frees the device to accept a new tone pair. The GT
output acts to reset the external steering time constant, and its state is a function of ESt and the voltage on St. (See
Common Crystal Connection on page 5).
18 VDD Positive power supply. (Normally connected to +5V.)
* -02 only. Connect to VSS for -01 version
Guard Time Adjustment
Where independent selection of signal duration and
interdigit pause are not required, the simple steering
circuit of Basic Steering Circuit is applicable.
Component values are chosen according to the formu-
la:
tREC = tDP + tGTP
tGTP @ 0.67 RC
The value of tDP is a parameter of the device and
tREC is the minimum signal duration to be recognized
by the receiver. A value for C of 0.1 µF is recommend-
ed for most applications, leaving R to be selected by
the designer. For example, a suitable value of R for a
tREC of 40 ms would be 300 k. A typical circuit using
this steering configuration is shown in the Single -
Ended Input Configuration on page 4. The timing
requirements for most telecommunication applications
are satisfied with this circuit. Different steering arrange-
ments may be used to select independently the guard
times for tone-present (tGTP) and tone-absent (tGTA).
This may be necessary to meet system specifications
that place both accept and reject limits on both tone
duration and interdigit pause.
registered. On the other hand, a relatively short tREC
with a long tDO would be appropriate for extremely
noisy environments where fast acquisition time and
immunity to dropouts would be required. Design infor-
mation for guard time adjustment is shown in the
Guard Time Adjustment below.
Power-down and Inhibit Mode (-02 only)
A logic high applied to pin 6 (PD) will place the device
into standby mode to minimize power consumption. It
Figure 5 Guard Time Adjustment
Guard time adjustment also allows the designer to tai-
lor system parameters such as talkoff and noise immu-
nity. Increasing tREC improves talkoff performance,
since it reduces the probability that tones simulated by
speech will maintain signal condition long enough to be
4
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stops the oscillator and the functioning of the filters.
On the M-8870-01 models, this pin is tied to ground
(logic low).
Inhibit mode is enabled by a logic high input to pin 5
(INH). It inhibits the detection of 1633 Hz. The output
code will remain the same as the previous detected
code (see Pin functions table on page 4). On the M-
8870-01 models, this pin is tied to ground (logic low).
Input Configuration
The input arrangement of the M-8870 provides a dif-
ferential input operational amplifier as well as a bias
source (VREF) to bias the inputs at mid-rail. Provision
is made for connection of a feedback resistor to the
op-amp output (GS) for gain adjustment.
Tone Decoding
FLOW
697
FHIGH
1209
Key (ref.)
1
697 1336
697 1477
770 1209
2
3
4
770 1336
770 1477
852 1209
5
6
7
852 1336
852 1477
941 1336
8
9
0
941 1209
941 1477
697 1633
S
#
A
770 1633
852 1633
941 1633
B
C
D
ANY ANY
ANY
L = logic low, H = logic high, Z = high impedance
Differential Input Configuration
OE
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
L
M-8870
In a single-ended configuration, the input pins are
connected as shown in the Single - Ended Input
Configuration on page 3 with the op-amp connected
for unity gain and VREF biasing the input at 1/2VDD.
The Differential Input Configuration bellow permits
gain adjustment with the feedback resistor R5.
DTMF Clock Circuit
The internal clock circuit is completed with the addition
of a standard 3.579545 MHz television color burst crys-
tal. The crystal can be connected to a single M-8870 as
shown in the Single - Ended Input Configuration on
page 3, or to a series of M-8870s. As illustrated in the
Common Crystal Connection below, a single crystal
can be used to connect a series of M-8870s by cou-
pling the oscillator output of each M-8870 through a 30
pF capacitor to the oscillator input of the next M-8870.
Q4 Q3 Q2 Q1
0 001
0 010
0 011
0 100
0 101
0 110
0 111
1 000
1 001
1 010
1 011
1 100
1 101
1 110
1 111
0 000
Z ZZZ
Common Crystal Connection
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M-8870
AC Characteristics
Parameter
Symbol Min
Typ*
Max
Units
Valid input signal levels (each tone
- -29 - +1 dBm
of composite signal)
- 27.5 -
869 mVRMS
Positive twist accept
- - - 10
dB
Negative twist accept
- - - 10
dB
Frequency deviation accept limit
- - - ± 1.5% + 2 Hz Nom.
Frequency deviation reject limit
- ±3.5% - - Nom.
Third tone tolerance
- -25 -16
-
dB
Noise tolerance
- - -12 -
dB
Dial tone tolerance
- +18 +22
-
dB
Tone present detection time
tDP 5 8 14
ms
Tone absent detection time
tDA 0.5
3
8.5
ms
Minimum tone duration accept
tREC - - 40
ms
Maximum tone duration reject
tREC 20
-
-
ms
Minimum interdigit pause accept
tID - - 40
ms
Maximum interdigit pause reject
tDO 20
-
-
ms
Propagation delay (St to Q)
tPQ - 6 11
µs
Propagation delay (St to StD)
tPStD
-
9
16
µs
Output data setup (Q to StD)
tQStD - 4.0
-
µs
Propagation delay (OE to Q), enable
tPTE - 50 60
ns
Propagation delay (OE to Q), disable
tPTD - 300
-
ns
Crystal clock frequency
fCLK 3.5759 3.5795 3.5831
MHz
Clock output (OSC2), capacitive load CLO - - 30
pF
All voltages referenced to VSS unless otherwise noted. For typical values VDD = 5.0 V, VSS = 0 V, TA = 25°C, fCLK = 3.579545 MHz.
*Typical figures are at 25°C and are for design aid only; not guaranteed and not subject to production testing.
Notes:
1. dBm = decibels above or below a reference power of 1 mW into a 600load.
2. Digit sequence consists of all 16 DTMF tones.
3. Tone duration = 40 ms. Tone pause = 40 ms.
4. Nominal DTMF frequencies are used, measured at GS.
5. Both tones in the composite signal have an equal amplitude.
6. Bandwidth limited (0 to 3 kHz) Gaussian noise.
7. The precise dial tone frequencies are (350 and 440 Hz) ± 2%.
8. For an error rate of better than 1 in 10,000.
9. Referenced to lowest level frequency component in DTMF signal.
10. Minimum signal acceptance level is measured with specified maximum frequency deviation.
11. Input pins defined as IN+, IN-, and OE.
12. External voltage source used to bias VREF.
13. This parameter also applies to a third tone injected onto the power supply.
14. Referenced to Single - Ended Input Configuration on page 3. Input DTMF tone level at -28 dBm.
Notes
1,2,3,4,5,8
2,3,4,8
2,3,5,8,10
2,3,5
2,3,4,5,8,9,13,14
2,3,4,5,6,8,9
2,3,4,5,7,8,9
See Timing Diagram on page 7
User adjustable (see Basic Steering
Circuit and Guard Time Adjustment
on pages 3 and 4.)
OE = VDD
RL = 10 k, CL = 50 pF
-
-
6
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Timing Diagram
M-8870
Explanation of Events
(A) Tone bursts detected, tone duration invalid, outputs not updated.
(B) Tone #n detected, tone duration valid, tone decoded and latched in outputs.
(C) End of tone #n detected, tone absent duration valid, outputs remain latched until next valid tone.
(D) Outputs switched to high impedance state.
(E) Tone #n + 1 detected, tone duration valid, tone decoded and latched in outputs (currently high impedance).
(F) Acceptable dropout of tone #n + 1, tone absent duration invalid, outputs remain latched.
(G) End of tone #n + 1 detected, tone absent duration valid, outputs remain latched until next valid tone.
Explanation of Symbols
VIN
ESt
St/GT
Q1 - Q4
StD
OE
tREC
tREC
tID
tDO
tDP
tDA
TGTP
TGTA
DTMF composite input signal.
Early steering output. Indicates detection of valid tone frequencies.
Steering input/guard time output. Drives external RC timing circuit.
4-bit decoded tone output.
Delayed steering output. Indicates that valid frequencies have been present/
absent for the required guardtime, thus constituting a valid signal.
Output enable (input). A low level shifts Q1 - Q4 to its high impedance state.
Maximum DTMF signal duration not detected as valid.
Minimum DTMF signal duration required for valid recognition.
Minimum time between valid DTMF signals.
Maximum allowable dropout during valid DTMF signal.
Time to detect the presence of valid DTMF signals.
Time to detect the absence of valid DTMF signals.
Guard time, tone present.
Guard time, tone absent.
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M-8870
Figure 9 Mechanical Dimensions
Tolerances for 18 - pin Dip
Inches
Metric (mm)
Min Max
Min Max
A-
.210
- 5.33
A1 .015
-
.38 -
b .014
.022
.36
.56
b2 .045
.070
1.1
1.7
C .008
.014
.20
.36
D .880
.920
23.35
23.37
E .300
.325
7.62 8.26
E1 .240
.280
6.10 7.11
e .100 BSC
2.54 BSC
ec 0°
15°
0° 15°
L .115
.150
2.92 3.81
Tolerances for 18 - pin Dip
Inches
Metric (mm)
Min Max
Min Max
A .0926
.1043
2.35
2.65
A1 .0040
.0118
.10
.30
b .013
.020
.33
.51
D .4469
.4625
11.35
11.75
E .2914
.2992
7.4
7.6
e .050 BSC
1.27 BSC
H .394
.419
10.00
10.65
L .016
.050
.40 1.27
Dimensions
mm
(inches)
8
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Worldwide Sales Offices
CLARE LOCATIONS
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Tel: 1-978-524-6700
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Tel: 1-949-831-4622
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http://www.clare.com
Clare, Inc. makes no representations or warranties with respect to
the accuracy or completeness of the contents of this publication
and reserves the right to make changes to specifications and
product descriptions at any time without notice. Neither circuit
patent licenses nor indemnity are expressed or implied. Except as
set forth in Clare’s Standard Terms and Conditions of Sale, Clare,
Inc. assumes no liability whatsoever, and disclaims any express or
implied warranty, relating to its products including, but not limit-
ed to, the implied warranty of merchantability, fitness for a partic-
ular purpose, or infringement of any intellectual property right.
The products described in this document are not designed,
intended, authorized or warranted for use as components in sys-
tems intended for surgical implant into the body, or in other appli-
cations intended to support or sustain life, or where malfunction
of Clare’s product may result in direct physical harm, injury, or
death to a person or severe property or environmental damage.
Clare, Inc. reserves the right to discontinue or make changes to its
products at any time without notice.
Specification: DS-M-8870-R3
©Copyright 2001, Clare, Inc.
All rights reserved. Printed in USA.
7/25/01





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