Designing Next-Generation Car Access Receiver Modules

Transcription

1 Designing Next-Generation Car Access Receiver Modules Michael Hahnen and Klaus Herhoffer /

2 Introduction In Atmel launched an innovative car access system featuring the lowest current consumption. This was achieved through the self-polling capability of the ATA receiver IC. ATA derivatives and second-generation RF receivers like the ATAx address new RF automotive application areas. These include tire pressure monitoring system (TPMS), remote start applications, and bi-directional RF links. With leading RF performance and a very reliable RF link, the third generation ATAx is yet another step ahead. This family includes transceiver and transmitter devices. There are Flash, user ROM, and ROMless versions that are pin, function, and RF-matching compatible. Maximum development re-use minimizes the design efforts for one- and two-way systems. This article describes how to migrate from the earlier ATA/ devices to the current ATA/, or to directly create a new design with Atmel's latest generation ATAx. Migration to the ATA/ Customers with an RF system based on Atmel's ATA/ UHF receiver ICs can easily upgrade their design to the current generation ATA/. The required modifications to the existing receiver system comprise some very minor software and hardware modifications. Software Modifications Both the ATA and the ATA/ are configured by the host controller via one bidirectional line. Both devices have the same internal registers with identical configuration content. You can easily migrate from ATA to ATA/ without any software changes in the host controller. Simply double-check the sleep time settings, since there are some minor timing differences that may require adaptation. Table lists the detailed sleep time changes. The ATA (formerly named UBM) and the ATA/ are likewise configured via one bidirectional line from the host controller. Two internal registers contain the receiver configuration, but the number of bits within the registers differs. To protect the ATA/ against unwanted register content change, the serial communication includes one additional bit. To enable writing content to the addressed register, set bit to low, and add it to the communication software routines in the host controller. Most bits in the registers do have the same meaning and cause the same hardware behavior. Tables and show the two devices' internal registers. Sleep MHz T sleep [ms] Table. Sleep Time Settings ATA ATA ATA MHz T sleep [ms] T sleep [ms] T sleep [ms] 0 cont. On cont. On cont. On cont. On cont. Off cont. Off cont. Off cont. Off Automotive Compilation Vol. 0

3 Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit0 Bit Bit Bit Bit OFF Command OP Register 0 BR_Range N Bitcheck V POUT Sleep X Sleep 0 Baud Baud0 BitChk BitChk0 POUT Sleep Sleep Sleep Sleep Sleep0 X Sleep Std X Sleep Temp (Default) LIMIT Register 0 0 min max 0 0 min min min min min min0 max max max max max max0 (Default) Table. ATA Register Content Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit 0 Bit Bit Bit Bit Bit OFF Command OP Register 0 BR_Range N Bit-check Modulation Baud Baud0 BitChk BitChk0 ASK/ _FSK Sleep X Sleep Noise Suppression Sleep Sleep Sleep Sleep Sleep0 X SleepStd Noise_ Disable 0 Default values of Bit LIMIT Register min max 0 0 min min min min min min0 max max max max max max0 0 Default values of Bit Table. ATA/ Register Content Bit in the OP register is different. The ATA uses bit to control output pin, whereas the ATA/ uses bit to switch between ASK and FSK mode. This switching is done in ATA by pin. The upgrade to ATA/ includes a different timing of the programming start pulse. You may also need to do some slight software modifications in the host controller. Please refer to the datasheet section "Programming Start Pulse". With the ATA, bit in the OP register extends the sleep time by a factor of, whereas the ATA/'s bit allows optional additional noise suppression. /

4 Hardware Changes The ATA/ is the direct upgrade of the ATA. Both devices are available in SSO packages with the same footprint, whereas the ATA package is an SO. Due to the ATA/'s hardware improvements you also need to do some hardware modifications on your board when migrating (table ). Faster external oscillator start-up with a negative resistor up to.kω (only valid for migration from ATA to ATA/) The ATA/ requires a crystal with a different frequency Less external components on the ATA/ board due to integration of the filter circuit The antenna matching elements have to be modified Pin ATA ATA ATA/ FSK/ASK IC_Active Open (RSSI) VS VS (with filter) Antenna matching (with filter) Antenna matching Antenna matching 0 NC NC VS VS NC Filter circuit Filter circuit XTAL XTAL XTAL XTAL POUT Data clock Enable High = polling on Low = sleep Polling High = polling on, Low = receiving active Table. List of Hardware Differences VCC X X + C.µF C 0nF JP R kω % R kω VS = +V X SMB C nf C nf C 0pF C pf Printed Inductor > nh C.pF C 00pF ± 0.pF L nf 0 SENS FSK/ASK CDEM A D MIXVCC LNA LNA_IN n.c. U UBM C 0nF all Inductors: Toko LLFH ENABLE TEST POUT XTO LF LF LFVCC R 0 C.nF C.nF Q.MHz HC/UH R Ω C0 nf C pf R 0kΩ R n.m. JP ENABLE Figure. Typical Application ATA Automotive Compilation Vol. 0

5 V S + C.µF % C 0nF C nf C 0nF C pf nh 0pF C 0 R kω to 0kΩ ATA SENS IC_ACTIVE POLLING /_ON CDEM TEST A MIXVCC LNA LNA_IN NC C 0 nf D _CLK XTO LF LF LFVCC V = V to V X. MHz Q R >.kω C C pf 0pF IC_ACTIVE Sensitivity Reduction POLLING/_ON _CLK COAX C.pF L nh C 00pF R Ω C C0.nF nf Figure. Typical Application with ATA VS RF_IN + C C.µF C L C nf C 0nF 0 SENS IC_ACTIVE CDEM TEST RSSI A LNAREF LNA_IN LNA R kω to 0kΩ ATA ATA ATA POLLING/_ON D _CLK XTAL XTAL TEST TEST C 0nF F Crystal R.kΩ CL CL RSSI IC_ACTIVE Sensitivity Reduction V X = V to V POLLING/_ON _CLK Figure. Typical Application with ATA/ /

6 VS 0 IRQ NSS MISO ATEST ATEST _IO _IO RFIN_LB A PB PB PB PB PB PB MOSI RFIN_HB PB SCK SAW SPDT_RX SPDT_ANT NC SPDT_RX Atmel ATA ATA ATA PB0 D PC CLK_IN Microcontroller NC PC VS_SPDT TEST _EN XTAL XTAL VS PC0 PC PC PC 0 VS = V VDD Figure. Typical Application Circuit with V Power Supply Automotive UHF Receiver Design Based on ATA// All members of Atmel's ATA// family include an AVR microcontroller core. Designed for the ISM frequency bands (0-MHz, -MHz and -MHz), these parts feature excellent RF receiving sensitivity. In FSK mode, the sensitivity reaches.dbm (at.mhz, 0.kbit/s and BWIF = khz), in ASK mode sensitivity is dbm (at.mhz, 0.kbit/s and BWIF = khz). The autonomous self-polling mode and good blocking performance help you to design robust automotive RF receiver systems with very low power consumption, since only a valid RF signal activates the host controller. Excellent RF performance, a short bill of materials, and flexibility to adapt the receiving behaviour to all known RF protocols and market needs make the ATAx family the best choice for new RF receiver designs. Configuration The AVR microcontroller's ROM includes firmware that allows you to configure the device according to the configuration stored in the EEPROM. You can control the receiver via an external host controller by using the SPI interface. User Flash and user ROM (available in ATA and ATA only) enable you to write additional software. For example, to protect the external host controller, or to adapt the firmware to any RF protocol. The receiver families have different program memory capabilities (see table ). Part Number ATA ROM Firmwave KByte User Flash User ROM V Power Supply Application In automotive remote keyless entry (RKE) systems, you use the ATAx as an UHF receiver inside the vehicle. Such applications typically connect to a regulated V power supply (see figure ). The host MCU controls the RF receiver via the SPI interface. The receiver operates autonomously. The host controller just enables the receiving mode, either polling RX mode or standard RX mode, by sending the corresponding command over the SPI lines. RF Settings In modern vehicles an RF receiver must be capable of receiving different RF protocols from different transmitters. This includes RKE key fobs, tire pressure monitoring systems, and remote start controls. Because these systems transmit their messages with different modulation, baud rate, and bandwidth, the ATAx family offers five different RF settings to let you define the RF protocol and the wake-up conditions via the EEPROM configuration GUI (graphical user interface). Reception Modes You can use two different reception modes. During standard Rx mode the receiver checks for a desired RF telegram at a particular time. Polling mode means that you define the telegram settings in advance. The receiver automatically and continuously checks for this defined setting. Once the receiver detects the beginning of a valid signal it switches to standard Rx mode and receives the message. In case of no valid message, the receiver switches off for a defined period, and the entire procedure starts over again. ATA KByte KByte ATA KByte KByte Table. Program Memory Automotive Compilation Vol. 0