HM 9270C/D
DTMF RECEIVER
General Description
The HM 9270C/D is a complete DTMF receiver integrating both the bandsplit filter and digital decoder
functions. The filter section uses switched capacitor techniques for high- and low-group filters and dial-tone
rejection. Digital counting techniques are employed in the decoder to detect and decode all 16 DTMF tonepairs into a 4-bit code. External component count is minimized by on-chip provision of a differential input
amplifier, clock-oscillator and latched 3-state bus interface.
Features
•
•
•
•
•
•
•
•
Complete receiver in an 18-pin package.
Excellent performance.
CMOS, single 5 volt operation.
Minimum board area.
Central office quality.
Low power consumption.
Power-Down mode (HM9270D only).
Inhibit-mode (HM9270D only).
Pin Configurations
HM9270C
IN+
IN
GS
VREF
IC*
IC*
OSC1
OSC2
VSS
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
HM9270D
VDD
IN+
IN
GS
St/GT
ESt
StD
Q4
Q3
Q2
Q1
TOE
VREF
INH
PWDN
OSC1
OSC2
VSS
* Connect to VSS
- 1 -
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
VDD
St/GT
ESt
StD
Q4
Q3
Q2
Q1
TOE
HM 9270C/D
DTMF RECEIVER
Block Diagram (Figure 1)
INH
HIGH
GROUP
FILTER
IN+
+
IN
-
GS
DIAL
TONE
FILTER
DIGITAL
ZERO
CROSSING
DETECTORS DETECTION
LOW
GROUP
FILTER
ALGORITHM
CODE
Q1
CONVERTER
Q2
AND
Q3
LATCH
Q4
CHIP
CHIP CHIP
CHIP
CLOCKS POWER BIAS REF
OSC2
BIAS
CIRCUIT
+
STEERING
LOGIC
-
OSC1
VDD V
SS
PWDN
VREF St/ GT
ESt
StD
TOE
Pin Description
Function
Pin
Sym.
1
2
IN+
IN-
Non-Inverting input
Connections to the front-end differential amplifier.
Invering Input
3
GS
Gain select. Gives access to output of front-end differential amplifier for connection of
feedback resistor.
4
VREF
Reference voltage output,nominally VDD/2. May be used to bias the inputs at midrail (see
application diagram).
5
INH
Inhibit (input) logic high inhibit the detection of 1633Hz internal built-in pull down resistor.
(HM9270D only).
6
PWDN
Power down (input). Active high power down the device and inhibit the oscillator internal
built-in pull down resistor. (HM9270D only).
7
8
OSC1
OSC2
Clock Input
Output
9
VSS
Negative power supply, normally connected to 0V.
TOE
3-state data output enable (input). Logic high enables the outputs Q1-Q4. Internal pull-up.
10
Clock
3.579545 MHz crystal connected between these pins completes
internal oscillator.
- 2 -
HM 9270C/D
DTMF RECEIVER
Function
Pin
Sym.
11
12
13
14
Q1
Q2
Q3
Q4
3-state data outputs. When enabled by TOE, provide the code corresponding to the last valid
tone-pair received (see code table).
15
StD
Delayed steering output. Presents a logic high when a received tone-pair has been registered
and the output latch 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 (bi-directional). 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; its state is a function of ESt and the voltage on St (see truth
table).
18
VDD
Positive power supply, +5Volts.
Absolute Maximum Ratings (Notes 1, 2 and 3)
Parameters
Min.
Max.
Units
Power Supply Voltage, VDD - VSS
6
V
Voltage on any pin
VSS - 0.3
VDD+ 0.3
V
Current at any pin
10
mA
o
Operating temperature
-40
+85
C
o
Storage temperature
-65
+150
C
Package power dissipation
500
mW
Note 1. Absolute maximum ratings are those values beyond which damage to the device may
occur.
2. Unless otherwise specified, all voltages are referenced to ground.
3. Power dissipation temperature derating: -12 mV/oC from 65oC to 85oC
DC Electrical Characteristics
Parameter Description
SUPPLY:
VDD
Icc
Po
IS
INPUTS:
VIL
VIH
IIH/IIL
Iso
RIN
VTSt
Operating Supply Voltage
Operating Supply Current
Power Consumption
Standby Current
Low Level Input Voltage
High Level Input Voltage
Input Leakage Current
Pull Up (Source) Current
Input
Signal
Impedance Inputs 1,2
Steering Threshold Voltage
Test Conditions
Min. Typ. Max. Units
4.75
f=3.579MHz; VDD=5V
PWDN pin = VDD
-
3.0
15
-
5.25
7
35
100
V
mA
mW
µA
1.5
V
V
uA
uA
MΩ
3.5
VIN=Vss or VDD
TOE (Pin 10)=OV
@ 1kHz
0.1
7.5
10
2.35
- 3 -
15
V
HM 9270C/D
DTMF RECEIVER
Parameter
OUTPUTS:
VOL
VOH
IOL
IOH
VREF
ROR
Description
Low Level Output Voltage
High Level Output Voltage
Output Low (Sink) Current
Output High (Source) Current
Output Voltage
VREF
Output Resistance
Test Conditions
Min.
No Load
No Load
VOUT=0.4V
VOUT=4.6V
No Load
Typ.
Max.
Units
0.03
4.97
2.5
0.8
1.0
0.4
2.4
V
V
mA
mA
V
KΩ
2.7
10
Operating Characteristics
Gain Setting Amplifier
Parameter
IIN
RIN
VOS
PSRR
CMRR
AVOL
fC
VO
CL
RL
VCM
Description
Input Leakage Current
Input Resistance
Input Offset Voltage
Power Supply Rejection
Common Mode Rejection
DC Open Loop Voltage Gain
Open Loop Unity Gain Bandwidth
Output Voltage Swing
Tolerable capacitive load(GS)
Tolerable resistive load(GS)
Common Mode Range
Test Conditions
Min.
Typ. Max.
VSS < VIN < VDD
±100
10
±25
60
60
65
1.5
4.5
100
50
3.0
1kHz
-3.0V <VIN< 3.0V
RL³100KΩ to VSS
No Load
Units
nA
MΩ
mV
dB
dB
dB
MHz
VPP
pF
KΩ
VPP
Notes : 1.All voltages referenced to VDD unless otherwise noted.
2.VDD= 5.0V, VSS = 0V, TA = 25oC .
AC Characteristics
All voltages referenced to VSS unless otherwise noted. VDD=5.0V, VSS=0V, TA = 25OC, FCLK=3.579545 MNz, using
test circuit of figure 2.
Parameter
Description
Min.
Typ.
SIGNAL COITIONS:
Valid Input Signal level (each
tone signal):MIN
MAX
-40
7.75
1,2,3,5,6,9,11
1,2,3,5,6,9,11
10
10
dB
dB
2,3,6,9,11
±1.5%±2 Hz
Nom.
Nom.
2,3,5,9,11
2,3,5,11
2,3,4,5,9,10,11
2,3,4,5,7,9,10,11
2,3,4,5,8,9,10,11
±3.5%
-16
-12
+18
- 4 -
Notes
dBm
mVRMS
dBm
mVRMS
+1
883
Twist Accept Limit: Positive
Negative
Freq. Deviation Accept Limit
Freq. Deviation Reject Limit
Third Tone Tolerance
Noise Tolerance
Dial Tone Tolerance
Max. Units
dB
dB
1,2,3,5,6,9,11
HM 9270C/D
DTMF RECEIVER
Parameter
Description
TIMING:
tDP
tDA
tREC
tREC
tID
tDO
Tone Present Detection Time
Tone Absent Detection Time
Tone Duration Accept
Tone Duration Reject
Interdigit Pause Accept
Interdigit Pause Reject
OUTPUTS:
tPQ
tPSED
tQSED
tPTE
tPTD
Propagation Delay (St to Q)
Propagation Delay (St to StD)
Output Data Set Up (Q to Std)
Propagation
ENABLE
Delay (TOE to Q) DISABLE
CLOCK:
fCLK
CLO
Crystal/Clock Frequency
Clock Output Capacitive
(OSC2)
Load
Min. Typ. Max.
Units
5
0.5
ms
ms
ms
ms
ms
14
4
16
8.5
40
20
40
ms
Adjustment"
8
12
4.5
50
300
11
60
3.5759 3.5795
Notes
Refer to Fig. 4
(User Adjustable)
Refer to "Guard Time
µs
µs
µs
ns
ns
TOE= VDD
RL=10kΩ
CL=50pf
3.581 MHz
30 pf
Notes: 1.dBm = decibels above or below a reference power of 1mW into a 600 Ohm load.
2.Digit sequences consists of all 16 DTMF tones.
3.Tone duration = 40mS Tone pause = 40mS.
4.Nominal DTMF frequencies are used.
5.Both tones in the composite signal have an equal amplitude.
6.Tone pair is deviated by ±1.5% ±2Hz.
7.Bandwidth limited (3kHz) Gaussian Noise.
8.The precise dial tone frequencies are (350Hz and 440Hz) ±2%.
9.For an error rate of less than 1 in 10,000.
10.Referenced to the lowest level frequency component in DTMF signal.
11.Added A 0.1µf capacitor between V DD and VSS.
Function Description
HM9270C
5V
0.1µf
IN+
100 NF
St/GT
IN
100 KΩ
100 KΩ
3.58
MHz
VDD
GS
ESt
VREF
StD
IC
Q4
IC
Q3
OSC1
Q2
OSC2
VSS
TOE
100 NF
300 KΩ
Q1
FIGURE 2. SINGLE ENDED INPUT CONFIGURATION
- 5 -
20
HM 9270C/D
DTMF RECEIVER
HM9270D
5V
0.1µf
IN+
100 NF
IN
Vin
100 KΩ
5V
100 KΩ
3.58
MHz
VDD
St/GT
GS
ESt
VREF
StD
INH
Q4
PWDN
Q3
OSC1
Q2
OSC2
VSS
Q1
100 NF
300 KΩ
TOE
FIGURE 3. SINGLE ENDED INPUT CONFIGURATION
The HM9270C/D 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 tones of receiver pair, 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 dual tone signal to the inputs of two
filters a sixth order for the high group and an eighth order for the low group. The bandwidths of which correspond
to the bands enclosing the low-group and high-group tones (see Fig. 4). The filter section also in corporates
notches at 350Hz and 440 Hz for exceptional dial-tone rejection. Each filter output is followed by a second-order
switched-capacitor 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 and noise; the
outputs of the comparators provide full-rail logic swings at the frequencies of the incoming tones.
Flow Fhigh KEY TOE Q4
Q3 Q2
697 1209
1
H
0
0
0
Decoder Section
697 1336
2
H
0
0
1
The decoder used digital counting techniques to
697 1477
3
H
0
0
1
determine the frequencies of the limited tones and to
770 1209
4
H
0
1
0
verify that they correspond to standard DTMF
770 1336
5
H
0
1
0
frequencies. A complex averaging algorithm(protects)
770 1477
6
H
0
1
1
against tone simulation by extraneous signals, such as
852 1209
7
H
0
1
1
voice, while providing tolerance to smalll frequency
852 1336
8
H
1
0
0
deviations and variations. This averaging algorithm has 852 1477
9
H
1
0
0
been developed to ensure an optimum combination of
941 1336
0
H
1
0
1
immunity to "talk-off" and tolerance to the presence of
941 1209
*
H
1
0
1
interfering signals ("third tones") and noise. When the
941 1477
#
H
1
1
0
detector recognizes the simultaneous presence of two
697 1633
A
H
1
1
0
valid tones (referred to as "signal condition" in some
770 1633
B
H
1
1
1
industry specifications), it raises the "early steering"
852 1633
C
H
1
1
1
flag (ESt). Any subsequent loss of signal condition will 941 1633
D
H
0
0
0
cause ESt to fall.
ANY L
Z
Z
Z
L = LOGIC LOW , H = LOGIC HIGH, Z = HIGH
IMPEDANCE
FIGURE 4. LOGIC TABLE
- 6 -
Q1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
Z
HM 9270C/D
DTMF RECEIVER
FIGURE 5. TIMING DIAGRAM
D
A
EVENTS
B
C
t REC
t REC
E
TONE # n
t
F
G
TONE DROPOUT
INTERDIGIT
PAUSE
t ID
TONE #n+1
t DO
TONE#n+1
t DA
DP
V Tst
ESt
t GTP
t
GTA
St/GT
t
DATA
OUTPUTS
Q1-Q4
DECODE TONE n-1
PQ
DECODED
TONE#n
t PS t D
DECODED TONE # n + 1
HIGH
IMPEDANCE
StD
OUTPUT
t
TOE
t
PTE
A. Short tone bursts: detected. Tone duration is invalid.
B. Tone #n is detected. Tone duration is valid. Decoded
to outputs.
C. End of tone #n is dectected and validated.
D. 3 State outputs disabled (high impedance).
E. Tone #n + 1 is detected. Tone duration is valid. De
coded to outputs.
F. Tristate outputs are enabled. Acceptable drop out of
tone #n + 1 does not negister at outputs.
G. End of tone #n + 1 is detected and validated.
10
FIGURE 5. TIMING DIAGRAM
50
STEERING CIRCUIT
60
PTD
0
20
30
40
Before registration of a decoded tone-pair, the receiver checks
70
for a valid signal duration (referred to as "character-recogni80
tion-condition"). This check is performed by an external RC time-constant driven by ESt.
1K
0
2K
A logic high on ESt causes VC (see Fig. 5) to rise as the
capacitor discharges. Provided signal-condition is maintained (ESt remains high) for the validation period (t GTP), Vc
reaches the threshold (VTSt) of the steering logic to register the
FIGURE 6. TYPICAL FILTER
tone-pair, latching its corresponding 4-bit code (see Fig. 3)
CHARACTERISTIC
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 recieved tone-pair has been registered. The contents of the output lacth are made available on the 4-bit
output bus by raising the 3-state control input (TOE) to a logic high. The steering circuit works in reverse to
validate the interdigit paues 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. The facility, together
with the capability of selecting the steering time-constants externally, allows the designer to tailor performance to
meet a wide variety of system requiremetns.
- 7 -
HM 9270C/D
DTMF RECEIVER
C
0.1µf
V DD
V DD
t
V DD
GTA =(RC) ln (
V TST
VC
St/GT
t
GTP
)
V DD
)
V DD - V
TST
=(RC) ln (
ESt
R
S tD
FIGURE 7. BASIC STEERING CIRCUIT
Guard Time Adjustment
In many situations not requiring independent selection of receive and pause, the simple steering circuit of Fig. 7 is
applicable. Component values are chosen according to the following formulae:
tREC = tDP + tGTP
tID = tDA + tGTA
The value of tDP is a parameter of the device (see table) and tREC is the minimum signal duration to be recognized by
the receiver. A value for C of 0.1 µF is recommended for most applications, leaving R to be selected by the
designer. For example, a suitable value of R for a tREC of 40mS would be 300k.
Different steering arrangements 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 which place both accept and reject limits on
both tone duration and interdigital 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 condition for long enough to be 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 drop - outs
would be required. Design information for guard-time adjustment is shown in Fig. 8.
V
VDD
DD
C
C
S t / GT
S t / GT
R1
R1
R2
ES t
ES t
VDD
VDD - VTST
VDD
tGTA=(R1 C) In (
)
VTST
R1R2
Rp=
R1+R2
tGTP=(Rp C) In (
R2
VDD
VDD - VTST
VDD
)
tGTA=(R1 C) In (
VTST
R1R2
Rp=
R1+R2
)
tGTP=(Rp C) In (
a) Decreasing tGTP (tGTP < tGTA)
b) Decreasing tGTP (tGTP > tGTA)
FIGURE 8. GUARD TIME ADJUSTMENT
- 8 -
)
HM 9270C/D
DTMF RECEIVER
Input Configuration
The input arrangement of the HM9270C/D provides a differential-input operational amplifier as well as a
bias source (VREF ) which is used to bias the inputs at mid-rail.
Provision is made for connection of a feedback resistor to the op-amp output (GS) for adjustment of gain.
In a single-ended configuration, the input pins are connected as shown in Fig. 2 with the op-amp connected
for unity gain and VREF biasing the input at 1/2V DD.
Fig. 9 shows the differential configuration, which permits the adjustment of gain with the feedback resistor
R5.
C1
HM9270C/D
R1
+
-
C2
R4
GS
R5
R3
R2
VREF
FIGURE 9. DIFFERENTIAL INPUT CONFIGURATION
Power - down and inhibit mode
A logic high applied to pin 6 (PWDN) will power the device to minimize the power consumption in a standby
mode. It stops the oscillator and the functions of the filters.
Inhibit mode is enabled by a logic high input to the pin 5 (INH). It inhibits the detection of 1633 Hz. The output
code will remain the same as the previous detected code (see table 1).
fLow
697
697
697
770
770
770
852
852
852
941
941
941
697
770
852
941
-
Fhigh Key
1209 1
1336 2
1477 3
1209 4
1336 5
1477 6
1209 7
1336 8
1477 9
1336 0
1209 *
1477 #
1633 A
1633 B
1633 C
1633 D
ANY
TOE Q4
H
L
H
L
H
L
H
L
H
L
H
L
H
L
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
L
L
Z
Q3
L
L
L
H
H
H
H
L
L
L
L
H
H
H
H
L
Z
Q2
L
H
H
L
L
H
H
L
L
H
H
L
L
H
H
L
Z
Q1
H
L
H
L
H
L
H
L
H
L
H
L
H
L
H
L
Z
fLow
697
697
697
770
770
770
852
852
852
941
941
941
697
770
852
941
-
Fhigh Key
1209 1
1336 2
1477 3
1209 4
1336 5
1477 6
1209 7
1336 8
1477 9
1336 0
1209 *
1477 #
1633 A
1633 B
1633 C
1633 D
ANY
TOE Q4
Q3 Q2 Q1
H
L
L
L
H
H
L
L
H
L
H
L
L
H
H
H
L
H
L
L
H
L
H
L
H
H
L
H
H
L
H
L
H
H
H
H
H
L
L
L
H
H
L
L
H
H
H
L
H
L
H
H
L
H
H
H
H
H
L
L
H
H
PREVIOUS DATA
H
H
L
Z
Z
Z
Z
Table 1: Truth table
INH =VSS
(Z: high impedance)
- 9 -
INH=VDD
HM 9270C/D
DTMF RECEIVER
SPECIAL PACKAGE PIN CONFIGURATIONS
HM9270DM
IN+
INGS
VREF
INH
PWDN
OSC1
OSC2
VSS
NC
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
- 10 -
VDD
St/GT
EST
StD
Q4
Q3
Q2
Q1
TOE
NC