processing IC, intended for automotive applications for
detecting intrusion into an ultrasound field where
automatic gain control (AGC) is not required or in
applications with a user sensitivity adjustment. The IC
was developed as an Application Configurable System
Cell (ACSC), either to be used as a stand alone circuit,
or as part of a larger custom circuit designed to suit
specific application requirements. The DA5546
contains all the circuit functions necessary to implement
an advanced low power, high sensitivity ultrasonic
movement detection system.
The synchronous demodulator system which monitors
both the magnitude and phase of the return signal gives
a significant improvement in sensitivity and noise
rejection compared to more basic systems. The logic
level alarm output of the DA5546 enables it to be part
of a microprocessor controlled security system. The
DA5546 is implemented in a 1.2um double poly double
metal CMOS process and runs from a single 5V supply
with a basic power consumption of 5mW (excluding
transmit sensor power). The device is available in a 20
pin SOIC package.
Features
•
Complete stand alone system
•
Sensitive to both amplitude
and
phase disturbances
•
5mW active power consumption
•
Synchronous demodulator to extract Doppler tones
caused by moving objects
•
A master clock oscillator with an external ceramic
resonator
•
A clock divider and transmit sensor driver
•
A low noise 40kHz preamplifier for the receive
sensor
•
Second order low-pass and high-pass filters to define
the Doppler frequency range and reduce the effect of
thermal air movement inside the vehicle
•
Threshold detector and time averaging integrator
reduces the effect of transient noise and wind
•
Compact 20 pin SOIC package
System Overview
The front-end bandpass filter removes out of band noise
and interference, particularly the effects of EMC, and
prevents amplifier overload.
The output of the
amplifier is fed to a synchronous demodulator. This
gives an output that is proportional to both the
amplitude
and
phase of the return signal giving a
significant increase in sensitivity, as the phase of the
return signal varies much more rapidly than the
amplitude when intrusions occur. An additional benefit
is the high degree of rejection of wideband noise since
only signals coherent with the transmitter excitation are
recognised.
The demodulator output is high-pass and low-pass
filtered and amplified to extract the Doppler tones
caused by moving object with velocities in the range of
0.1m/s to 2m/s. Further gain is applied to the signal
together with a second high-pass/low-pass filter, to
remove the effects of slow air movement caused by
convection currents inside the vehicle. The output of
the second filter is monitored by a window comparator
with +/-200mV thresholds: any Doppler tones larger
than this will cause the integration capacitor connected
to the CEV pin to be charged up. When this capacitor
is charged to 2.5V the alarm output pin ALR will go
high. If no Doppler tones are present then the
integration capacitor is discharged at a much slower
rate. With a capacitor of 47nF fitted between the CEV
pin and ground, Doppler tones must be present for a
least 400ms before the ALR output goes high.
Dialog Semiconductor
Rev. B, 4-October-97
1
DA5546
Functional Block Diagram
IBIAS
AGND
VDD
VSS
Bias
Generator
V
mid
Generator
X1
X2
TXH
4MHz
Oscillator
Clock
Divider
TXL
RXH
RXL
EMC Filter
20-80KHz
40KHz
Preamplifier
Synchronous
Demodulator
PSD
BOP
+0.2
-
+
+
Doppler
Filter
FIN
-
+
+
-
Window
comparator
-
+
+
BIN
ALR
-
-
Event integrator
-0.2
30dB gain
CEV
CAL
CAH
FOP
Application Notes
A single 5 volt power supply is required. The resistor
connected between IBIAS and VDD is used to define
the internal operating bias currents. The chip alone
typically takes approximately 1mA without a transmit
head connected, and 2 - 3 mA with a typical transmit
head. The chip generates its own mid-rail reference
supply of 2.5V which is brought out at the A
GND
pin
for decoupling (mandatory). Most of the internal
analog circuitry is referenced to this voltage. The
operating current of the internal circuitry is set by the
resistor between the I
BIAS
pin and the 5 volt supply.
The DA5546 requires a 4MHz ceramic resonator which
may be of the two or three pin variety. If the resonator
has two pins (as shown) then the correct loading
capacitors must be connected as specified by the
resonator manufacturer. If a three pin resonator is used
then these capacitors are included internally and the
user simply needs to ground the centre pin.
The DA5546 must be used with 40kHz piezoelectric
heads. These are available from several manufacturers
in a wide variety of sizes and styles. In general the
smaller transducers have lower sensitivity. The DA5546
chip provides a differential output drive at the TXH &
TXL pins to drive the transmit head at 10 volts pk-pk.
The polarity of the transmit head is unimportant. If a
reduced output can be accepted, then the transmit head
may be connected between either TXH or TXL and 0
volts to reduce the power consumption.
The receive head should be connected with the case or
'low' side to RXL and the isolated or 'high' side to RXH.
Note that the RXL pin is connected to the A
GND
reference voltage internally and should
not
be
connected to 0V externally.
Dialog Semiconductor
Rev. B, 4-October-97
2
DA5546
Application Notes (Continued)
The capacitor connected between pins CEV and ground
sets the integration time. A value of 47nF will give
approximately 400ms. Intrusions must persist for this
time before the ALR pin goes high.
Convection current effects cause air movement which
increase rapidly as the interior temperature of the car
rises. Opening the ventilation outlets on the dashboard
also increases these problems. The effect of air
movement is to create large Doppler signals in the 0 to
1 Hz frequency band, whereas signals caused by
intrusions are in the 10 to 170 Hz band. Since the air
movement effects occupy a different frequency band
than the wanted signals, they can be removed by
filtering. However, these signals can be very much
larger than the wanted signals (up to 50dB), so
discrimination is improved with a higher order filter.
In the diagrams below (Figures 2 & 3) various
configurations of air movement filter are shown :
- Figure 2 shows a simple 2nd order passive high-pass
filter with variable gain. This is necessary for correct
operation of the system as it provides good
discrimination between air movement and slow
moving objects. To increase the sensitivity, increase
the value of the 180kΩ resistor and decrease the value
of the parallel 4.7nF capacitor connected between FIN
and FOP. To decrease the upper Doppler limit,
increase both the series 15nF capacitor connected to
CAH and the parallel 4.7nF capacitor between FIN
and FOP. To increase the lower Doppler limit,
decrease the parallel 47nF capacitor between CAH
and CAL and decrease the series 100nF capacitor
connected to PSD.
For single vehicle type applications, a fixed gain may
be employed as the interior parameters of the
application will not change. In this case, the 20kΩ
variable resistor may be omitted and the other filter
components optimised.
- Figure 3 shows a 3rd order active filter with variable
gain using the uncommitted buffer op-amp available
at pins BIN and BOP. This will give improved
discrimination between air movement and slow
moving objects over the passive filters shown in
Figure 2. To decrease the upper Doppler limit,
increase both the series 15nF capacitor connected to
CAH and the parallel 2.2nF capacitor between FIN
and FOP. To increase the lower Doppler limit,
decrease the parallel 47nF capacitor between CAH
and CAL and decrease the two series 100nF
capacitors connected to PSD.
The ALR pin is the active high alarm output and is both
TTL and CMOS level compatible.
47nF
40KHz
receiver
33pF
1
BIN
CEV
RXH
A
VDD
1MΩ
RXL
X2
X1
BOP
4MHz
ceramic
resonator
33pF
A
VSS
DA5546
+5V
VDD
AGND
VSS
TXH
TXL
ALR
AVDD
IBIAS
15nF
47nF
68ΚΩ
CAH
CAL
PSD
100nF
FIN
FOP
180ΚΩ
4.7nF
10µF
10µF
0V
AVSS
40KHz
transmitter
ALR
20KΩ min
Figure 2 - Simple Filter
Dialog Semiconductor
Rev. B, 4-October-97
3
DA5546
47nF
40KHz
receiver
100k
Ω
33pF
1
BIN
CEV
RXH
A
VDD
1MΩ
RXL
X2
X1
BOP
4MHz
ceramic
resonator
33pF
A
VSS
DA5546
+5V
VDD
AGND
VSS
TXH
TXL
ALR
10µF
10µF
0V
AVSS
AVDD
IBIAS
15nF
47nF
130ΚΩ
CAH
CAL
PSD
100nF
100nF
FIN
FOP
330ΚΩ
2.2nF
40KHz
transmitter
ALR
20KΩ min
Figure 3 - Extra Air Movement Rejection Filter with Variable Gain
Pin Description
Pin Number
.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
BOP
Pin Name
BIN
CEV
RXH
RXL
IBIAS
CAH
CAL
PSD
FIN
FOP
ALR
TXL
TXH
VSS
AGND
VDD
X1
X2
Functional Description
Input to buffer amplifier
Integrator filter capacitor
Receive transducer signal input
Receive transducer signal common
Bias current input for internal circuitry
2nd LP/HP capacitor
2nd HP capacitor
Demodulator output to 1st filter
1st filter input
1st filter output
Active high alarm output
Transmit transducer anti-phase drive
Transmit transducer in-phase drive
Negative supply
Internally derived mid-rail reference
Positive supply
Oscillator input from ceramic resonator
Oscillator output to ceramic resonator
Not connected
Output from buffer amplifier
Dialog Semiconductor
Rev. B, 4-October-97
4
DA5546
Absolute Maximum Ratings
V
DD
to V
SS
______________________________________-0.3V, + 7V
All other pins ___________________________ V
SS
- 0.3V, V
DD
+0.3V
Continuous power dissipation __________________________500mW
Operating temperature range _____________________ -40°C to +85°C
Storage temperature range _____________________ -65°C to +1 60°C
Lead temp (Soldering, 10 sec) __________________________ +300°C
Stresses beyond those listed under 'Absolute Maximum Ratings' may
cause permanent damage to the device. These are stress ratings only and
functional operation of the device at these or any other conditions beyond
those indicated in the operational sections of the specification is not
implied. Exposure to absolute maximum rating conditions for extended
periods may affect device reliability.
Electrical Characteristics
Specified at V
DD
= +5V and V
SS
= 0V and T
amb
= 25°C, F
xtal
= 4MHz, I
bias
= 4µA
Parameter
Return signal at RXH pin for correct operation
Input impedance at RXH pin
Window comparator thresholds
AGND out voltage
TXH, TXL output swing with 1kΩ load
V
DD
supply current without Tx head
Min
0.2
50
±180
2.4
1.0
Max
20
200
±220
2.6
4.0
1.5
Units
mV rms.
kΩ
mV
V
V
mA
NB. Typical transmit heads will add 0.5 - 5mA to the supply current depending on the head type and whether
differential or single ended drive is used.
About TEMIC Semiconductors
TEMIC is the microelectonics enterprise of Daimler-
Benz. The Semiconductor Division of TEMIC includes
Telefunken Semiconductors, Siliconix, Matra MHS,
and Dialog Semiconductor. A leader in the design of
semiconductor
products
for
communications,
automotive, computer, hi-rel, industrial, and consumer
applications, TEMIC’ worldwide semiconductor
s
operations include ISO-9001 certified manufacturing
facilities in Europe, the United States, and Asia/Pacific.
Sales are handled by the worldwide TEMIC network
and by regional sales representatives and distributors.
Successfully combining analog and digital functions on
the same ASIC (Application-Specific Integrated
Circuit) is the key to true system integration. TEMIC
Semiconductors’ years of experience in mixed signal
ASIC technology gives our customers the ability to
achieve the integrated solutions their systems need.
TEMIC Semiconductors’ extensive mixed signal design
and manufacturing expertise was acquired vial the
specialist company Dialog Semiconductor, which
became part of the TEMIC group in 1992. TEMIC
Semiconductors is a leading supplier of mixed signal
technology, and we support all types of mixed signal
solutions in CMOS, from the initial idea through to
volume production.
This Publication is issued to provide outline information only which (unless agreed by Dialog Semiconductor in writing) may not be used, applied or
reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to products or services concerned. Dialog
Semiconductor reserves the right to alter without notice the specification , design, price or conditions of supply of the product. Customer takes note that
Dialog Semiconductor’ products are not designed for use in devices or systems intended for supporting or monitoring life nor for surgical implants into
s
the body. Customer shall notify the company of any such intended use so that Dialog Semiconductor may determine suitability. Customer agrees to
indemnify Dialog Semiconductor for all damages which may be incurred due to use without the company’ prior written permission of product in such
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