MV8870-1 Datasheet PDF - GEC Plessey Semiconductors

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MV8870-1
GEC Plessey Semiconductors

Part Number MV8870-1
Description Integrated DTMF Receiver
Page 12 Pages


MV8870-1 datasheet pdf
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THIS DOCUMENT IS FOR MAINTENANCE
PURPOSES ONLY AND IS NOT
RECOMMENDED FOR NEW DESIGNS
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MV8870/MV8870-1
ADVANCE INFORMATION
DS3140-2.1
MV8870 / MV8870-1
INTEGRATED DTMF RECEIVER
The MV8870 / MV8870-1 is a complete DTMF receiver
integrating both the bandsplit filter and digital decoder
functions, fabricated in GPS’s double-poly ISO2-CMOS
technology. The filter section uses switched capacitor
techniques for high and low group filters; the decoder uses
digital counting techniques to detect and decode all 16 DTMF
tone pairs into a 4-bit code.
External component count is minimised by on-chip
provision of a differential input amplifier, clock oscillator and
latched 3-state bus interface.
The MV8870 and MV8870-1 are functionally identical, but
differ in Electrical Characteristics.
FEATURES
s Complete DTMF Receiver
s Low Power Consumption
s Internal Gain Setting Amplifier
s Adjustable Guard Time
s Central Office Quality
et4U.com APPLICATIONS
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s Receiver Systems for BT or CEPT Specifications
s Paging Sytems
s Repeater Systems / Mobile Radio
s Credit Card Systems
s Remote Control
IN+
IN-
GS
VREF
SEL
PD
OSC1
OSC2
VSS
1
2
3
4
5
6
7
8
9
18 VDD
17 St/GT
16 ESt
15 StD
14 Q4
13 Q3
12 Q2
11 Q1 DG18
10 TOE DP18
MP18
VREF 5
NC 6
SEL 7
FHT 8
FH 9
PD 10
NC 11
25 StD
24 NC
23 NC
22 FLT
21 FL
20 Q4
19 Q3
HP28
Figure 1: Pin connections - top view
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SEL PD
5(7) 6(10)
1(1)
IN+
2(2)
IN-
3(3)
GS
CHIP CHIP
POWER BIAS
FHT
(8)
HIGH GROUP FILTER
FH
(9)
DIAL TONE FILTER
ZERO
CROSSING
DETECTORS
LOW GROUP FILTER
DIGITAL
DETECTION
ALGORITHM
CODE
CONVERTER
AND LATCH
BIAS CIRCUIT
CHIP
CLOCKS
STEERING LOGIC
11(17)
Q1
12(18)
Q2
13(19)
Q3
14(20)
Q4
10(16)
TOE
18(28) 9(14)
VDD VSS
4(5)
VREF
(22) 7(12) 8(13)
FLT OSC1 OSC2
(21)
FL
16(26)
ESt
15(25)
StD
17(27)
St/GT
Figure 2: Functional block diagram (Pin numbers in brackets refer to HP package)
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MV8870/MV8870-1
FUNCTIONAL DESCRIPTION
STEERING CIRCUIT
The MV8870 / MV8870-1 monolithic DTMF receiver offers
small size, low power consumption and high performance. Its
architecture consists of a bandsplit filter section, which
separates the high and low tone groups, followed by a digital
counting section which verifies the frequency and duration of
the received tones before passing the corresponding code to
the output bus.
FILTER SECTION
Separation of the low-group and high-group tones is
achieved by applying the DTMF signal to the inputs of two
sixth-order switched capacitor band-pass filters, the
bandwidths of which correspond to the low and high group
frequencies. The filter section also incorporates notches at 350
and 440 Hz for exceptional dial tone rejection (see Fig.3). Each
filter is followed by a single order switched capacitor filter
section which smooths the signals prior to limiting. Limiting is
performed by high-gain comparators which are provided with
hysteresis to prevent detection of unwanted low-level signals.
The outputs of the comparators provide full rail logic swings at
the trequencies of the incoming DTMF signals.
For testing and monitoring, the high and low group filter
and zero crossing detector outputs are made available via
FHT, FH, FLT and FL (HP package only).
Before registration of a decoded tone-pair, the receiver
checks for a valid signal duration (referred to as (character
recognition condition). This check is performed by an external
RC time constant driven by ESt. A logic high on ESt causes the
voltage at the SVGT pin (VSt/GT) to rise as the capacitor
discharges (see Figs.4 and 5).
Provided signal condition is maintained (ESt remains high)
for the validation period (tGTP), VSUGT reaches the threshold
(VTSt) of the steering logic which allows it to register the tone
pair and strobe the corresponding 4-bit code into the output
latch (see Fig.6). At this point the SVGT pin is activated as an
output and drives VSt/GT to VDD (see Fig.5).
St/GT continues to drive high as long as ESt remains high.
After a short delay (tDP) to allow the output latch to settle, the
delayed steering output pin (StD) goes high to indicate that the
code for a new received tone-pair is available. The contents of
the output latch are output onto the output bus (Q1 to Q4 pins)
when the three-state output enable (TOE) pin is 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 (drop-out) too short to be
considered a valid pause. This facility, together with the
capability of selecting the steering time constants externally,
allows the designer to tailor performance to meet a wide
DECODER SECTION
variety of system requirements.
Following the filter section is a decoder employing digital
counting techniques to determine the frequencies ot the
VDD
incoming tones and to verify that they correspond to standard
DTMF frequencies. A complex averaging algorithm protects
C
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against tone simulation by extraneous signals such as voice
while providing tolerance to small frequency deviatioDnastaaSndheet4U.com
variations. This averaging algorithm has been developed to
ensure an optimum combination of immunity to talk-off and
tolerance to the presence of interfering frequencies (third
tones) and noise. When the detector recognises the
VDD
MV8870/ St/GT
MV8870-1 ESt
StD
18
17
16
15
R
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simultaneous presence of two valid tones (this is referred to as
the ‘Signal Condition’ in some industry specifications) the Early
Steering output (ESt) will go to an active state. Any
subsequent loss of signal condition will cause the ESt pin to go
tGTA = RC In {VDD ÷ VTSI}
tGTP = RC In {VDD ÷ (VDD - VTSU)}
to its inactive state (see Fig.5).
Figure 4: Basic Steering Circuit
0
10
ATTENUATION
(dB)
20
30
40
50
XY
ABC D
EF G
H
200 400 600
800 1000 1200
FREQUENCY (Hz)
1400 1600
1800
2000
Precise
Dial Tones
X = 350 Hz
Y = 440 Hz
DTMF Tones
A = 697 Hz
B = 770 Hz
C = 852 Hz
D = 941 Hz
E = 1209 Hz
F = 1336 Hz
G = 1477 Hz
H = 1633 Hz
2
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Figure 3: Filter response
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MV8870/MV8870-1
APPLICATIONS
A simple application circuit is shown in Fig.7. This has a
symmetric guard time circuit, a single-ended analog input and
a dedicated crystal oscillator.
GUARD TIME ADJUSTMENT
In many situations not requiring seperate selection of tone
duration and interdigit pause, the simple steering circuit shown
in Fig.7 is applicable. Component values are chosen according
to the formulae (see Figs. 4, 8a and 8b):-
tREC = tDP + tGTP
tlD = tDA + tGTA
The value of tDP is a device parameter (see Dynamic
Characteristics and Fig.5) and tREC is the minimum signal
duration to be recognised by the receiver. Likewise tDA is a
device parameter (Fig.5) and tlD is the minimum time taken to
recognise an interdigit pause. A value for C2 of 0.1µ-F is
recommended for most applications, leaving R3 to be selected
by the designer.
Different steering arrangements may be used to select
independantly the guard times for tone present (tGTP) and tone
absent (tGTA). This may be necessary to meet system
specifications which place both accept and reject limits on both
tone duration and interdigit pause. Guard Time adjustment
also allows the designer to tailor system parameters such as
talk-off and noise immunity. Increasing tREC improves talk-off
performance since it reduces the probability that tones
simulated by speech will maintain signal conditions long
enough to be registered. Alternatively a relatively short tREC
wim a long tlD would be appropriate for extremely noisy
environments where fast acquisition time and immunity to tone
drop-outs are required. Design information for guard time
adjustment is shown in Figs. 8a and 8b.
A B C EF
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VIN
ESt
St/GT
tDA
tDP tDP
TONE N
tDA
tDP
VTSt
TONE N + 1
TONE N + 1
tDA
tDA tDP
tDA
tDP
t < tGTP t < tGTP
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t = tGTP
t = tGTA
t = tGTP
t < tGTA
t = tGTA
StD
CODE
CONVERTER
LATCH
OUTPUTS
TOE
tPStD
DECODED TONE N-1
tPQ
tPStD
TONE N
tPStD
tPQ
TONE N + 1
tPStD
Q1 - Q4
D
TONE N
TONE N + 1
D
D
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EXPLANATION OF EVENTS
A, Tone bursts detected, but tone duration invalid and output latch unchanged.
B. Tone N detected, tone duration valid, output latch updated and new data signalled by
StD.
C. End of tone N detected, tone absent duration valid, but output latch updated until next
valid tone.
D. Outputs switched to high impedance.
E. Tone N + 1 detected, tone duration valid, tone decoded, output latch updated
(although outputs are currently high impedance) and new data signalled by StD.
F. Acceptable dropout of tone N + 1, tone absent duration invalid, StD and output latch
unchanged.
G. End of tone N + 1 detected, tone absent duration valid, StD goes low but output latch
not updated until next valid tone.
NOTES
1. tDP time for valid tone present is
a device parameter (see Electrical
Characteristics).
2. tDA time for valid tone absent is
a device parameter (see Electrical
Characteristics).
3. tGTP and tGTA are adjustable via
external RC network at pins 16
and 17 (see Fig. 4).
4. tPSID and tPQ are propogation
delays given in Electrical
Characteristics.
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Figure 5: Timing diagram
3
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