AS8412

AS8412 AMSCO | Alldatasheet

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AUTOMOTIVE SONAR INTRUSION Data Sheet March 2001

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 2 of 14 Key Features

• True sonar/pulse-echo operation
• Wide dynamic range
• Programmable sensitivity levels
• Self-adaptive to vehicle interiors
• Self-adaptive to temperature and environmental changes
• High sensitivity to intrusion
• Immunity to false alarms
• Detection of sabotage attempts
• Compatible with standard 40 kHz ultrasonic transducers
• No adjustments needed at factory or at field
• Few external components
• Time reference: external clock or oscillator based on crystal/ceramic resonator
• Built-in self-test
• Internal power-on-reset
• Advanced CMOS technology
• Low power consumption: 0.65 to 1.0 mA
• Operation between -40°C and +85 °C
• Available in 20-pin DIP and 20-pin SOIC package General Description The AS8412 is a signal processing IC designed to implement reliable, high-performance sonar intrusion detectors. It generates short 40 kHz bursts to feed an ultrasonic tran s- ducer. The resulting sonar waves are reflected on the vehicle interior and the echoes are received by another transducer. Inside the AS8412, the electrical signal is first submitted to an analog conditioning circuit, then it is digitized and processed by a DSP, whose out- put is analyzed by a discriminator based on fuzzy-logic techniques. Thus, true intrusion conditions can be discerned from natural phenomena and other allowable disturbances. No adjustments are necessary at factory or at the field, as the AS8412 is self-adaptive to the physical and environmental conditions. Compact and EMI-resistant intrusion detec- tors are made possible, due to the small number of components. Block Diagram PRE- AMP BAND-PASS FILTER AGC ENVELOPE DETECTOR A / D CONVERTER D S P DISCRIMINATOR MODULATOR / DRIVER CONTROL LOGIC OSCILLATOR SIGNALLING VCAP SAS SENS 1 SENS 0 ALEN LED WARN ALARM SEL40K OSCIN OSCOUT TX1 TX2 RX

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 3 of 14 Pin Description AS8412 Pin # Name Description 1 TX1 40-kHz burst generator - output 1. 2 OSCIN Clock input or crystal / ceramic resonator connection. 3 OSCOUT Crystal / ceramic resonator connection. Not connected when external clock is applied. 4 VCAP Pin for programming capacitor at the envelope detector. 5 AVDD Analog supply voltage (+5V). 6 AGND Analog ground. 7 RXGND Analog ground. 8 RX Ultrasonic echo input.

9 SEL40K Time reference select input (SEL40K=’1’ to select 40 kHz or SEL 40K=’0’ to select 400 kHz

at OSCIN). 10 ALEN Alarm enable input (when ALEN =’0’, the outputs ALARM, WARN and LED are disabled). 11 SENS0 Sensitivity selection (least significant bit). 12 SENS1 Sensitivity selection (most significant bit).

13 SAS SAS enable input (SAS=’1’ activates Self-Adjusting Sensitivity, SAS=’0’ keeps sensitivity

fixed) 14 TP Test / reset pin. A rising edge resets the IC. This pin should be left unconnected or tied to VDD for normal operation. 15 VDD Digital supply voltage (+5V).

16 GND Digital ground

17 LED Active-low signalling LED output (open drain). 18 WARN Active-low auxiliary alarm output (open drain). 19 ALARM Active-low main alarm output (open drain). 20 TX2 40-kHz burst generator - output 2. Pinout & Packaging Available Package(s):

• 20 pin DIP
• 20 pin SOIC TX1 OSCIN OSCOUT VCAP AVDD AGND RXGND RX SEL40K ALEN TX2 ALARM WARN LED GND VDD TP SAS SENS1 SENS0

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 4 of 14 Absolute Maximum Ratings Conditions: 1. AII voltages referenced to GND 2. AVDD connected to VDD 3. AGND connected to GND Supply Voltage < 7V Input Pin Voltage -0,3 V to VDD + 0.3 V Output Pin Voltage -0,3 V to VDD + 0.3 V Power dissipation 500 mW Operating temperature under bias -40 °C to +85 °C Storage Temperature -65 °C to +150 °C Latch-up immunity -10mA … + 10mA Note: Stresses above these values may cause permanent damage to the device. Functional operational at these values is not implied ESD immunity / HBM: 1500 Ohm; 100 pF Recommended Operating Conditions Parameter Symbol Min Typ Max Units Supply Voltage (VDD, AVDD) VDD 4.5 5.0 5.5 V Operating Temperature Range TO -40 - 85 °C Clock Frequency (SEL40K=1) FCK 39 40 41 kHz AC Peak Voltage at RX Input VIN 0.1 - 10 mV D.C. Electrical Characteristics (VDD = 5 V, VSS = Ground, TA = -40 °C to +85 °C) Parameter Symbol Min Typ Max Units Conditions Low Level Input Voltage Vil - - 1.5 V Pins 2, 9, 11, 12, 13 High Level Input Voltage Vih 3.5 - - V Pins 2, 9, 11, 12, 13 Low-to-High Threshold Vt+ - 3.0 3.5 V Pin 10 (Schmitt Trigger Input) High-to-Low Threshold Vt- 1.4 1.8 - V Pin 10 (Schmitt Trigger Input) Hysteresis Vh 0.6 - - V Pin 10 Low Level Input Current Iil -1 - - µA Pins 9, 10, 11, 12, 13, (VDD=5 V) High Level Input Current Iih - - 1 µA Pins 9, 10, 11, 12, 13, (VDD=5 V) Input Resistance Rin - 200 - kΩ Pin 8

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 5 of 14 Low Level Output Voltage Vol - 0.5 0.5 0.5 V V V Pins 1, 20 Pins 18, 19 Pins 17 Iol=3 mA Iol=4 mA Iol=12mA High Level Output Voltage Voh 4.0 - - V Pins 1, 20 Ioh=-3 mA High-Z Output Current Ioz - - 10 µA Pins 17, 18, Vo=5V Total Supply Current Idd - 0.65 1.0 1.0 1.6 mA mA SEL40K= 1 SEL40K= 0 crystal or clock ceramic reson ator C1=C2=100pF A.C. Electrical Characteristics (VDD = 5 V, VSS = Ground, TA = 25°C) Parameter Symbol Min Typ Max Units Conditions Power-on-reset width tpor 50 500 500 530 800 ms SEL40K= 0, resonator / clock SEL40K= 1, clock SEL40K= 1, crystal Self-test delay (incl. tpor) tstd 1.3 1.7 1.7 1.4 1.9 2.1 s SEL40K= 0, resonator / clock SEL40K= 1, clock SEL40K= 1, crystal Fault indication pulse width tstw 4.3 - 4.6 s ALARM low pulse width tal 200 - - ms Pins 18, 19 LED low pulse width tonn 977 ms ms narrow = no detection wide = detection LED high pulse width toff - 888 - ms System Description Ultrasonic intrusion detectors are very popular in vehicle security systems, due to their low cost, good area coverage and easiness of installation. The AS8412 uses the sonar principle to build a high-performance intrusion detector that follows the requirements of the OEM automo- tive industry. As very short ultrasonic bursts are sent, the power needed to drive the transmitter is reduced. Interference and signal cancellation effects, present in systems with continuous transmission, are virtually eliminated. Fig. 1 shows the pulse/echo timing generated by the AS8412. The basic concept behind the AS8412 is the detection of changes in the relative position of objects inside the vehicle, by monitoring successive echo patterns with a discriminator based on fuzzy-logic. Despite the higher complexity of this approach, that demands both analog and digital signal processing, the solution is made cost-effective with the use of a single IC and a small number of external components.

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 6 of 14 TX pulse Echo in RX 44,4ms 0,6ms Fig. 1 - Pulse/Echo Timing Supply / Power-On Reset The AS8412 requires a single 5-volt power supply. Pins for VDD and GND are separated for the analog and digital circuits, and a 100 nF ceramic decoupling capacitor is recommended for each pair. There is an internal power-on-reset circuit that initializes the IC after each power-up. The VDD rise time must be less than 20 ms, to guarantee proper initialization. Optionally, the IC can also be reinitialized with a rising-edge at the pin 14, if requested by the application. Time Reference A clock must be present at the OSCIN input. The frequency may be selected to be either 40 kHz or 400 kHz, by setting the SEL40K input to ‘1’ or ‘0’ respectively. For the 40 kHz clock a duty-cycle of approximately 50% is necessary. The clock signal can be created in several possible ways:

• Generation by a microprocessor or other external circuit
• Built-in oscillator with an external 40-kHz crystal between OSCIN and OSCOUT. Depending on the crystal, a load capacitor (about 22 pF) may be needed at OSCOUT.
• Built-in oscillator with an external 400-kHz ceramic resonator between OSCIN and OSCOUT. Load capacitors of at least 100 pF are necessary at the pins, according to the resonator speci- fications. The IC power consumption increases with higher capacitor values (Idd= 1.0 mA with 100 pF capacitors). Ultrasonic Transducers The AS8412 is compatible with standard 40 kHz ultrasonic transducers, available from several manufacturers. For each IC, one transducer is used to transmit the sonar pulses and one other to receive the echoes reflected inside the vehicle. Internal lengths up to 3.5 meters can be cov- ered. In most applications, just two pairs of sensors will be used. The sensors will typically be posi- tioned at the B-pillars (central pillars), close to the roof, to provide the best possible coverage of

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 7 of 14 all the vehicle interior. Each pillar may have either a transmitter/receiver pair or two sensors of the same kind. The first arrangement is recommended, as it allows a single box at each pillar containing the AS8412 and the transducer pair controlled by it, thus decreasing cabling. The outputs TX1 and TX2 drive the transmitter in a push-pull configuration with 10 V peak-to- peak. As shown in Fig. 1, the transmission duty-cycle is very short (around 1/75), reducing the average current needed to generate the ultrasonic bursts to about 0.05 mA per IC. Shielded cable is mandatory for the receiver and recommended for the transmitter, unless they are adjacent to the IC. The shield at the receiver cable must be grounded and connected to the RXGND pin. Analog Conditioning The analog front-end, composed of a preamplifier and a filter centered at 40 kHz, increases the signal level and removes noise outside the bandpass. It is followed by a digitally controlled AGC amplifier, which keeps signal level at the VCAP output within prescribed levels. Finally, an en- velope detector extracts the information embedded in the amplified echo signal. The front-end needs proper bias during power-up. That can be provided by an RC series circuit to VDD, as shown at Fig. 2, or alternatively, by the pre-amplifier of Fig. 4. VDD 100n 100k To RX-Pin Fig. 2 - Series-RC circuit at RX The AS8412 has a wide dynamic range, to follow the signal fluctuations that occur in a large variety of vehicles, sensors and environmental conditions. Only under extreme conditions, like in a larger vehicle, an external pre-amplifier at RX may help to improve performance. A practical way to verify if a pre-amplifier might be useful, is by monitoring the echo waveform at VCAP. A FET-input buffer (input impedance at least 109 ohm) should be used, as the output impedance at VCAP is very high. 0 10 20 30 40 T(ms) Period = 44,4 ms VCAP(V) 3,0V-4,2V 1,3V-1,8V Fig. 3 - Waveform at VCAP

tion, so the manufacturer can adapt the detector to different requirements.

• Digital programming by the pins SENS1 and SENS0: controls the criteria used by the dis- criminator to validate intrusions or movements. Four sensitivities are available, as shown at Table 1.

Table 1. Digital programmable sensitivities

• Capacitor at the pin VCAP: controls the analog processing of the echo signal at the enve- lope detector. With smaller capacitors, the digitized echo signal will have a higher resolution and, as a result, a higher sensitivity will be obtained. The best combination of digital programming and VCAP capacitor is usually determined by experiment. A generally good choice is to use sensitivity mid-high and 270-pF capacitor at VCAP.

Table 2. Sensitivity as Function of Digital and VCAP Programming rough idea of how the SAS can affect the detector sensitivity, for a given capacitor at VCAP. The SAS actuation is controlled by the SAS input.

• SAS enabled (pin SAS = “1”): After power-on, the IC starts with the lowest sensitivity within the programmed range. The sensitivity will be constantly adjusted, according to the external conditions. Even under quiet conditions, the IC may take at least 2 minutes to reach the maximum allowed sensitivity. That should be considered during system evaluation.

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 10 of 14

• SAS disabled (pin SAS = “0”) The IC will keep the sensitivity fixed at the upper limit of the programmed range, regardless of the environmental conditions. This mode can be useful in special applications that de- mand a fixed or externally controlled sensitivity. The VCAP capacitor may have to be up to 4 times bigger than it would be with the SAS enabled, to compensate the fixed high sensitivity and avoid false alarms. Another use of this mode is to allow an easier characterization of the upper sensitivity limit during the system development. The self-test indicates an error with SAS=”0”. To generate a valid self-test, SAS must be ‘I’ during power-up. It may be switched afterwards. Together with the AGC, the SAS loop provides improved controllability over the intrusion detec- tion process, allowing the system to be little affected by changes in the external conditions, such as temperature, supply voltage and sensitivity of the ultrasonic sensors. In any case, the sensitivity can be very significant, so the AS8412 is not adequate to be used in convertibles or with open windows. DSP and Fuzzy-Logic Discriminator Many external phenomena may affect the ultrasonic waves inside the vehicle. Sunlight, blows at the glasses or roof, wind through the ventilation flaps are some examples. Experiments have shown that a real intrusion can not be validated by a single specific charac- teristic of the echo waveform. Several parameters must be observed at the same time and also how they correlate with each other. Experimental data gathered from extensive field test- ing were used to support the detection criteria embedded in the AS8412. To implement those criteria, first the digitized echoes are processed by a DSP circuit to en- hance the parameters to be monitored. Then, a fuzzy-logic discriminator continuously exam- ines how those parameters change and correlate, to verify any possible intrusion. Built-In-Self-Test When power is applied and SAS = ”1”, the AS8412 goes automatically into a self-test routine that checks the IC operation. It can also detect initialization errors due to a slow supply rise time or a clock problem at OSCIN. During the self-test period, the IC outputs are exercised and should be ignored. If the test is successful, normal operation starts, indicated by the output LED pulsing periodically. In the case of an IC malfunction, immediately after the self-test the LED and WARN outputs are turned on (low) for about 4.4 seconds. If a light-emitting diode is connected to the LED output, the self-test message may be seen directly by the user. After an error message, the LED starts to blink again, as in a normal operation. Fig. 6 shows the possible self-test waveforms after power-on.

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 11 of 14 VDD WARN DON’T CARE DON’T CARE tstd toff tonn VDD WARN DON’T CARE DON’T CARE tonntoff tstd ( a ) ( b ) stwt Fig. 6 (a) Self-Test OK (b) Error at Self-Test Alarm Signalling The AS8412 can indicate not only intrusion or motion, but also other kinds of disturbance, and send a particular message for each situation. Those disturbances are defined as follows and the messages are identified at Table 3.

• Weak intrusion: early stages of an intrusion, or a weaker intrusion or movement. Detection criteria are similar to those for intrusion, but with higher sensitivity.
• Blockage: elimination of the coupling between the transducers, either by blocking one of them, or by cutting a wire.
• Saturation: very strong 40-kHz signal at RX, possibly an attempt to sabotage the alarm system by saturating the receiver. May also be caused by a glass breakage or by strong hits with hard objects at the glass. With this signalling scheme, the IC has flexibility to be used either in simpler applications or in sophisticated microprocessor based systems. In addition, the manufacturer has the option to choose which kind of disturbance should be an alarm condition. The pulse widths are those specified in the AC electrical Characteristics and shown in Fig. 7. At ALARM and WARN they are at least 200ms; the outputs remain active if intrusion or motion persists. The WARN output could be used instead of the ALARM, if only intrusion detections should be flagged. In this case, the digital sensitivity should be scaled one step ower (for instance from mid-high to mid-low), or the capacitor at VCAP increased, to keep approximately the same sensitivity.

ous alarm triggering. Detection of glass breakage by saturation is not guaranteed. Table 3. Disturbances detected by the AS8412 or to block self-test pulses at ALARM and WARN.

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 13 of 14 Application Circuits The AS8412 is designed to provide a flexible utilization, so many application circuits are possi- ble. Only two of them are presented. The Application Circuit I of Fig. 8a is suitable to be used in a microcontroller-based alarm sys- tem. The 40-kHz clock is synthesized by the microcontroller, that also controls the digital sen- sitivity. By having access to all the signalling outputs, the alarm system can be programmed to signalize any combination of the disturbances detectable by the AS8412. This arrangement uses a minimum number of components to implement an intrusion detector. TX1 OSCIN OSCOUT VCAP AVDD AGND RXGND RX SEL4OK ALEN TX2 ALARM WARN LED GND VDD TP SAS SENS1 SENS0 UT1 40kHz from µ-Processor N.C. C1VDD 100n 100k 100n UT2 To µ-Processor Programmable Sensitivity (Digital) SAS Control N.C. VDD VDD C3 100n Fig. 8a - Application Circuit I TX1 OSCIN OSCOUT VCAP AVDD AGND RXGND RX SEL4OK ALEN TX2 ALARM WARN LED GND VDD TP SAS SENS1 SENS0 100k 100p UT2 VDD Programmable Sensitivity (Digital) N.C. VDD 100n VDD VDD N.C.C2 100p C3 100n 100n UT1 CR1 R1 D1 To Control Unit Fig. 8b - Application Circuit II

High Performance Automotive Sonar Intrusion – Data Sheet AS8412 March 2001 Page 14 of 14 The Application Circuit II of Fig. 8b can be used in a simpler system, that does not need micro- controller. A 400-kHz oscillator is built with a ceramic resonator. By using just the ALARM out- put, the system is able to detect intrusion, blockage and saturation as alarm of the operation and of the IC self-test diagnostic. A courtesy time is provided by R3 and C7. EMI Protection The usual precautions against EMI, such as PCB with ground plane, short tracks and shielded cables, are recommended for AS8412 applications, to avoid possible effects from noise in- duced by external sources. The RX cable must be shielded, because of the low-voltage signal. An alternative to protect other pins directly connected to unshielded cables, is to clamp induced voltages with signal diodes close to the pins (Fig.9) If a single shielded cable is used for the transmitting sensor, the internal wire may be con- nected to TX1 and the shield connected to TX2. In this case, only the TX2 output will need pro- tection diodes IC VDD (a) (b) Fig. 9 - Diode Clamp Protection for Unshielded Cables (a) pins 1, 20 (b) pins 17, 18, 19 Copyright  2000, Austria Mikro Systeme International AG, Schloß Premstätten, 8141 Unterpremstätten, Austria. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing by the copyright holder. To the best of its knowledge, Austria Mikro Systeme International asserts that the information contained in this publication is accurate and correct. IC