EVB71081 868/915mhz transmitter evaluation board description 390127108101 1 of 8 evb description rev. 003 aug/02 general description the th71081 antenna board is designed to optimally match the differential power amplifier output to a loop antenna. the th71081 board is populated for ask transmission. the evaluation board contains a differential-drive loop antenna printed on the pcb (printed circuit board). the size of the loop antenna is matched to the resonant frequency.. board layout data in gerber format is available on request. features ! fully integrated, pll-stabilized vco ! flexible frequency range from 850 mhz to 930 mhz ! ask achieved by on/off keying of internal power amplifier ! wide power supply range from 2.2 v to 5.5 v ! high over-all frequency accuracy ! very low standby current ! adjustable equivalent radiated power (erp) range from -20 dbm to -6 dbm ! adjustable current consumption from 6.2 ma to 12.5 ma ! differential output well-suited for loop antenna ! conforms to en 300 220 standard ordering information part no. EVB71081-868 EVB71081-915 applications ! keyless car and central locking ! low-power telemetry ! alarm and security systems ! general digital data transmission ! general analog audio signal transmission
EVB71081 868/915mhz transmitter evaluation board description 390127108101 2 of 8 evb description rev. 003 aug/02 theory of operation general as depicted in fig.1, the th71081 transmitter consists of a fully integrated voltage-controlled oscillator (vco), a divide-by-32 divider (div32), a phase-frequency detector (pfd) and a charge pump. an external loop filter at pin lf determines the dynamic behaviour of the pll and suppresses reference spurious signals. the vco?s output signal feeds the power amplifier (pa). rf signal power p o can be adjusted in six steps from p o = ?15 dbm to +1 dbm either by changing the value of resistor r 1 or by varying the voltage v ps at pin ps/data. the open-collector differential output (out1, out2) can be used to either directly drive a loop antenna or to be converted to a single-ended impedance by means of a balanced-to-unbalanced (balun) transformer. for maximum available output power, the differential output should be matched to a load of approx. 1 k ? . bandgap biasing ensures stable operation of the ic at a power supply range of 2.2 v to 5.5 v. ask modulation the th71081 can be ask-modulated by applying data directly at pin ps. this turns the pa on and off and therefore leads to an ask signal at the output lo source many applications require a stable rf source. for this purpose, the th71081 can be used without modulation as an easy-to-use, pll-stabilized, continuous wave (cw) generator. mode control logic the mode control logic allows two different modes of operation as listed in the following table. the mode control pin entx is pulled-down internally. this guarantees that the whole circuit is shut down if this pin is left floating. entx mode description 0 tx disabled whole circuit in standby 1 tx enable tx active table 1: modes of operation output power selection typical values at t a = 23 c and v cc = 3 v: r1 / k ? ? ? ? 0 7.5 11 15 24 43 r2 / k ? ? ? ? 4.7 4.7 4.7 4.7 4.7 v ps / v 2 1.1 0.9 0.7 0.5 0.3 i cc / ma 12.5 9.5 8.5 7.8 7.0 6.2 p o / dbm 1 -2 -5 -8 -12 -15 p harm / dbm -40 -40 -40 -45 -45 -50 table 2: output power selection if the transmitter is operated at any supply voltage v cc , the values for r 1 and r 2 can be calculated as allows: ? ? ? ? ? ? ? ? ? ? = 1 2 1 ps cc v v r r for more detailed information, please refer to the latest th71081 data sheet revision.
EVB71081 868/915mhz transmitter evaluation board description 390127108101 3 of 8 evb description rev. 003 aug/02 block diagram fig. 1: th71081 block diagram with external components lf 1 8 vee out1 out2 pa vcc 7 6 mode control vco pfd xosc div32 charge pump rf1 cf2 cf1 2 ro xtal cx1 ps/data 4 vcc 5 entx 3
EVB71081 868/915mhz transmitter evaluation board description 390127108101 4 of 8 evb description rev. 003 aug/02 circuit diagram c4 out2 xtal cx r1 rf1 cf1 cf2 c5 data gnd 1 2 vcc vee out1 ro lf entx ps data c6 vcc gnd 1 2 entx gnd vcc 12 3 r2 c1 5 6 7 8 1234
EVB71081 868/915mhz transmitter evaluation board description 390127108101 5 of 8 evb description rev. 003 aug/02 pcb top view board size is 34mm x 36mm board connection vcc power supply (2.2 v to 5.5 v) entx mode control pin (see table 1) data input for ask data (cmos) gnd several ground pins melexis 868/915mhz th71081_2 antenna board entx gnd gnd vcc vcc gnd data th71081 4 1 85 xtal cx1 c5 c4 c6 cf1 rf1 cf2 r2 r1 1 11 c1
EVB71081 868/915mhz transmitter evaluation board description 390127108101 6 of 8 evb description rev. 003 aug/02 board component values part size value 868.3 mhz value 915 mhz tolerance description cf1 0805 4.7 nf 10 nf 10% loop filter capacitor cf2 0805 56 pf 56 pf 10% loop filter capacitor cx 0805 82 pf 82 pf 5% xosc capacitor for ask, trimmed to f c c1 0603 0.82 - 1.2 pf 0.82 - 1.2 pf 2% antenna tuning capacitor c4 0805 330 pf 150 pf 10% blocking capacitor c5 0805 330 pf 150 pf 10% blocking capacitor c6 0805 220 nf 33 nf 10% blocking capacitor rf1 0805 1.5 k ? 1.5 k ? 10% loop filter resistor r1 0805 11 k ? see table 2 0 ? see table 2 10% ask power-select resistor, not requirement at cw mode r2 0805 4.7 k ? see table 2 nip see table 2 10% ask or cw mode power-select resistor xtal hc49/s 27.1344 mhz fundamental wave 28.5938 mhz fundamental wave 30ppm calibration 30ppm temp. crystal, c load = 12 pf to 15 pf, c 0, max = 7 pf, r m, max = 40 ? pcb loop antenna long side length 20 mm 20 mm on fr4 pcb material side length including length of c1 pcb loop antenna small side length 11 mm 11 mm on fr4 pcb material pcb loop antenna line width 2 mm 2 mm on fr4 pcb material nip ? not in place, may be used optionally the listed component values are default values. all values might be changed to fit to any specific application. pads for c1 are for population of a fixed-value capacitor with size 0805 or a to use trimming capacitor either.
EVB71081 868/915mhz transmitter evaluation board description 390127108101 7 of 8 evb description rev. 003 aug/02 package information fig. 2: soic8 all dimension in mm, coplanarity < 0.1mm d e1 e a a1 e b l min 4.80 3.81 5.80 1.32 0.10 1.27 0.36 0.41 0 max 4.98 3.99 6.20 1.72 0.25 0.46 1.27 8 all dimension in inch, coplanarity < 0.004? min 0.189 0.150 0.2284 0.060 0.0040 0.05 0.014 0.016 0 max 0.196 0.157 0.2440 0.068 0.0098 0.018 0.050 8 123 d e1 e b e a1 a l
EVB71081 868/915mhz transmitter evaluation board description 390127108101 8 of 8 evb description rev. 003 aug/02 disclaimer devices sold by melexis are covered by the warranty and patent indemnification provisions appearing in its term of sale. melexis makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. melexis reserves the right to change specifications and prices at any time and without notice. therefore, prior to designing this product into a system, it is necessary to check with melexis for current information. this product is intended for use in normal commercial applications. applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life- support or life-sustaining equipment are specifically not recommended without additional processing by melexis for each application. the information furnished by melexis is believed to be correct and accurate. however, melexis shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interrupt of business or indirect, special incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. no obligation or liability to recipient or any third party shall arise or flow out of melexis? rendering of technical or other services. ? 2002 melexis nv. all rights reserved. for the latest version of this document. go to our website at www.melexis.com or for additional information contact melexis direct: europe and japan: all other locations: phone: +32 1367 0495 phone: +1 603 223 2362 e-mail: sales_europe@melexis.com e-mail: sales_usa@melexis.com qs9000, vda6.1 and iso14001 certified
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