[love_galaxy]

السلام عليكم ورحمة الله وبركاته

اخواني مختصي الاتصالات الاسلكيه......
اريد طرح فكرة ارسال البيانات سواءا الكتابيه او الصوتيه او ما شابه بين جهازين
كمبيوتر ولكن باستخدام ترددات الراديو لارسال البيانات عبرها

والمشروع اشبه بمشروع ارسال الصوت بالليزر اي باستخدام serial port على جهاز الكمبيوتر لنقل الداتا الى دارة تقوم بتحويل البيانات لنقلها عبر اشعة الليزر بين المرسل والمستقبل ولكن المسافه التي تصلها اشعه الليزر محدودة وغير مجديه

لذلك لو تم نقل هذة الداتا عن طريق دارة راديو fm بدل الليزر لتصل مسافات اكبر و وفي اي مكان :atu:

فكل من يستطيع ان يفيد في هذا المشروع فجزاه الله خيرا

[mohamed aa]

1
Andreas Laute
Manager Application Lab
Thesys GmbH
Design Engineering
Haarbergstraße 67
D-99097 Erfurt, Germany
laute_andreas*thesys.de
Two 868MHz Transmitter Concepts – A Comparison between SAWs and
PLLs
Introduction
Applications in the new European short-range devices (SRD) band at 868 to 870 MHz are
demanding for appropriate solutions for low power transmitters and receivers to build up economic
wireless communication links. Transmitter systems for SRDs can be distinguished either
from their type of modulation or from the kind the RF carrier is practically generated. In the
first category, we can mainly differentiate between amplitude and frequency modulation, while
the second category can be essentially divided into SAW-based and PLL-based solutions. The
later comparison shall be the content of this paper. For 868MHz SRDs, FM or FSK transmission
should be preferred because to the receiver a strong interfering 900MHz GSM signal appears
as an AM blocker (due to the GSM burst mode).
Both transmitter concepts are compared with respect to some important parameters
such as power consumption, RF output power, frequency tolerance, FSK/FM feasibility, temperature
characteristics, reliability and price. Finally the pros and cons of each type of transmitter
are judged in order to give the potential user a guideline whether he may use the PLLbased
or SAW-based version.
Today the most economic way to design a PLL-TX is to use only one fully integrated
circuit (IC) that contains all components for frequency synthesis and modulation generation
(because costumers want high-quality, reliable and cheap solutions). For the SAW-TX there
are mainly two circuit configurations: a Colpitts oscillator employing a one-port SAW resonator,
or a Pierce oscillator that uses a two-port SAW device. A number of different 868MHz
transmitter designs have been developed by the author, therefore the presented performance
comparisons are strongly based on practical design experiences. Among them are, for example,
that for the SAW-TX the two-port resonator Pierce is the better choice if high efficiency and
good frequency stability are essential.
A PLL Transmitter using an RFIC
Circuit Description
The PLL-TX circuit is based on the RFIC TH7108 [1]. It is manufactured in a 0.8μm
BiCMOS process featuring a transition frequency of ft = 15 GHz. This RFIC is housed in a
SSOP16 and can be used at power supply voltages ranging from Vcc = 2.1 to 5.5 V and operates
at a temperature range from –40 to +85 °C. Some blocks of the PLL-TX are: a PLL synthesizer
with reference oscillator, a fully integrated VCO, a power amplifier, a standby and
biasing circuitry and a mode-control logic. The RFIC allows four different modes of operation:
2
the whole TX active, the whole TX shut down, external clock only and TX only. The externalclock
feature can be used to drive a micro controller with a 3.4MHz clock signal.
The PLL feedback divider ratio is 32, which means that the RF carrier frequency fc can
be set by choosing a crystal with a reference frequency fref = fc / 32. For fc = 868.3 MHz (the
center frequency of the first 868MHz SRD sub-band) we need fref = 27.1344 MHz. For this
frequency, fundamental-wave quartz crystals can still be easily manufactured. FSK modulation
is achieved by pulling the series resonant frequency of the crystal through the data. The Colpitts
reference oscillator requires two external capacitors that can be selected by the user to set
the exact center frequency fc and frequency deviation Df. Optionally an external varactor diode
can be added in series to the crystal to generate analog FM. Other PLL components are a
phase/frequency detector, a charge pump and a loop filter. Only the later requires three passive
off-chip components to optimize the loop bandwidth for lowest phase noise. The VCO is a ring
oscillator that can be used for the frequency range of 700 to 1000 MHz. So, operation at other
RFs, as for example in the US 915MHz ISM band, is no problem. RF output power can be
selected either by applying a resistor (between 15k and 68k) or a voltage (of 0.3V to Vcc) to
the power-select (PS) pin. ASK modulation can be achieved via output power modulation at
the same pin. An open-collector differential output is ideally suited to match a high-impedance
loop antenna. Our test board contains a balun impedance transformation network for singleended
drive of a 50W spectrum analyzer or for direct connection of a l/4 monopole antenna.
Fig. 1 shows the schematic of the complete PLL transmitter for FSK operation.
Fig. 1: 868MHz FSK transmitter utilizing the TH7108 PLL-TXIC
Parameters
The following table gives a parameter variation overview but is restricted to some fundamental
performance issues as there are: current consumption Icc, output power Po, 2nd and 4th harmonics
P2 and P4, respectively, center frequency fc and FSK deviation Df. All parameters have
been measured over full power supply (Vcc) and temperature range (Ta).
3
Vcc / V Icc / mA Po / dBm P2 / dBm P4 / dBm fc / MHz Df / kHz
Ta = -40 °C
2.1 8.2 -1.0 -44 -54 868.336 49
3.0 9.1 -0.4 -41 -49 868.335 50
5.5 9.8 0.5 -40 -41 868.334 51
Ta = 23 °C
2.1 9.4 -0.2 -42 -46 868.347 50
3.0 10.0 0.4 -39 -42 868.346 50
5.5 10.8 1.4 -39 -36 868.346 51
Ta = 85 °C
2.1 10.1 -1.2 -47 -43 868.353 50
3.0 10.6 -0.8 -48 -40 868.352 51
5.5 11.2 0.0 -49 -42 868.352 52
Table 1: Some parameters of the PLL-TX vs. Vcc and Ta
In order to visualize the performance of the transmitter, some spectrum plots are shown below
under nominal conditions (3 V, 23 °C).
Fig. 2: Output signal and harmonics
Fig. 3: Output power, phase noise and reference spurs (display lines indicate EN 300 220 limits)
4
Fig. 4: FSK modulation (frequency lines indicate first 868MHz sub-band)
A SAW-based Transmitter
Circuit Description
Designing a SAW-based TX means to start with the selection of a circuit topology and then to
chose an appropriate SAW resonator. One-port SAWs have two terminals and can therefore be
compared to crystals; and indeed well-known crystal oscillator topologies, as for example the
Colpitts, can be used, but with much more difficulties in getting the oscillator to work well
(because of the much higher frequency). The author’s first 868MHz SAW-TX designs utilized
such one-port resonators; they worked, but frequency stability versus power supply and temperature
variations was unacceptable for SRD production parts. Therefore, a two-port SAW
has been used for the final design.
The SAW resonator R2709 can be well modeled using the equivalent circuit given by
the manufacturer [2]. First, the design started with harmonic balance simulations on a singlebipolar
Pierce. Then the circuit was optimized for maximum power output and minimum current
consumption by adding a second bipolar as a booster. Fig. 5 depicts the circuit diagram of
the final SAW-TX with FM/FSK ability, which has been further optimized by hand tuning.
Fig. 5: 868MHz SAW-TX with two-port SAW resonator and two bipolars
5
Parameters
Unlike the PLL-TX, the SAW-TX has been characterized only within the temperature range of
Ta = -20 °C to 55 °C; this is the general extreme temperature range specified in EN 300 220-1
[3]. Using the SAW-TX outside this temperature range is possible but degrades center frequency
stability and usable modulation range (frequency deviation drops). Also the upper
power supply limit must be restricted to 3.8 V (or 3.3 V at –20 °C), but the lower limit can be
2.0 V (instead of 2.1 V at the PLL-TX). Under nominal conditions, the SAW-TX can operate
at 10 mA while delivering approx. 10 dBm into a 50W load. Harmonics stay below –30 dBm,
but with very small headroom at maximum supply voltage. This might be a problem when using
the SAW-TX with an antenna (discussed later). The following table shows the parameter
variations of current consumption Icc, output power Po, 2nd and 3rd harmonics P2 and P3, respectively,
center frequency fc and FSK deviation Df.
Vcc / V Icc / mA Po / dBm P2 / dBm P3 / dBm fc / MHz Df / kHz
Ta = -20 °C
2.0 5.3 4.8 -37 -41 868.392 46
3.0 9.5 9.9 -36 -33 868.413 61
3.3 10.8 10.9 -35 -32 868.432 53
Ta = 23 °C
2.0 5.8 4.5 -36 -42 868.355 14
3.0 10.1 9.8 -34 -35 868.372 29
3.8 13.8 12.1 -32 -31 868.402 56
Ta = 55 °C
2.0 6.1 4.3 -38 -42 868.284 8.5
3.0 10.6 9.3 -36 -36 868.294 15
3.8 14.3 12.0 -32 -32 868.303 25
Table 2: Some parameters of the SAW-TX vs. Vcc and Ta
Spectrum plots under nominal conditions (3V, 23°C) are listed below.
Fig. 6: Output signal and harmonics
6
Fig. 7: Output power and phase noise (same span used as with PLL-TX in Fig. 3)
Fig. 8: FSK modulation (frequency lines indicate first 868MHz sub-band)
Performance Comparison
The two 868MHz transmitters are presented with respect to some design issues and have been
compared to their most important parameters. Both can be used for FSK or FM applications in
the first SRD sub-band that ranges from 868.0 to 868.6 MHz. Here signals can be transmitted
with a power level of up to 25 mW (14 dBm).
The PLL-TX has been used at 1 mW (0 dBm) only. The RFIC TH7108 can be used at
power levels of up to approx. 2 mW (3 dBm). The main constraint that must be considered
here is that the current consumption should be less than (or equal to) 10 mA to allow the costumer
to use a Lithium cell battery; these cells typically should not be used at higher currents
to prevent them from early discharge. Therefore, the power-select resistor has been chosen to
deliver 0dBm output power at 10mA DC current. Choosing the desired carrier frequency for
any 868MHz sub-band means to select a crystal with appropriate reference frequency. This is
not a big deal because inexpensive crystals can be ordered at numerous manufacturers with
typical lead times of a few weeks. Therefore, the PLL-TX offers great frequency flexibility.
Using the PCB of the PLL-TX with an antenna causes no problem. All radiated harmonics are
at the same relative level below the fundamental output signal as with a 50W termination
7
(spectrum analyzer). This is because all active parts of the transmitter are on-chip, so there is
no chance for distributed spurious emissions anywhere on the PCB.
The SAW-TX delivers 10 mW (10 dBm) under nominal conditions but can also be used
up to 16 mW (12 dBm), at Vcc = 3.8 V. Due to the high efficiency, current consumption is only
10 mA nominal (same as PLL-TX). Unfortunately, there are only a few 868MHz SAW resonators
currently available at some fixed resonant frequencies (e.g. for 868.3, 868.35 or 868.95
MHz). This means that the SRD developer has to accept the given frequencies for his applications,
or has to spend a lot of money for a costumized SAW. Generally we can say that, at
least with today’s technology, SAWs cannot be taken for the designated narrow-band alarm
channels at 868MHz. This is because of their inherently poor frequency stability. Antenna
measurements showed that effective radiated power at the 4th harmonic is up to 5 dB higher
than –30 dBm, and hence not within the EN 300 220-1 requirements (note that this is not the
case at the 50W conductive measurement). This implies that the PCB radiates. A solution
would be to put the PCB into a grounded metal box. But this is a cost factor which might not
be acceptable.
Conclusions
Finally a fair comparison of both transmitter technologies based on the presented design examples
is summarized in the following table. This may help the user of 868MHz SRDs to find
“his” choice of transmitter architecture. Of course, the reported designs are exemplary, so the
author does not claim to show the absolute best features reachable with a PLL nor with a SAW
transmitter. But even with some variations at any parameter on either circuit (which might be
achieved with other transmitters), the reported data serve as a comparative guideline.
Issue PLL-TX SAW-TX
efficiency = Po/(Icc*Vcc) 3.7 % 34 %
frequency stability
vs Vcc and Ta
+7 / -9 kHz
+8 / -10 ppm
+60 / -88 kHz
+69 / -101 ppm
FSK deviation stability
vs Vcc and Ta
+2 / -1 kHz +32 / -20 kHz
reliability or ease of
production
- high -
fully integrated chip with only
few passive components
- medium -
manufacturing tolerances are
critical due to lot of Ls and Cs
type approval no problem with harmonics
phase noise limits max. output
no problem with phase noise
harmonics are critical
price - low -
net component costs are approx.
5.5 to 6.5 DM at 10k units
- medium -
net component costs are approx.
7.5 to 9.5 DM at 10k units
Table 3: Comparison of several SRD issues
References
[1] TH7108 – 868/915MHz FSK/ASK/FM Transmitter, Preliminary Data Sheet, Rev. 1.2, August
1999, Thesys GmbH.
[2] R2709 – SAW Resonator, Preliminary Data, June 25 1998, Siemens Matsushita Components.
[3] EN 300 220-1 – European Standard (Telecommunications Series), V1.2.1 (1997-11), European
Telecommunications Standard Institute (ETSI).

[نايف نظمي]

مشكور اخي على الشرح الوفي والكامل


بس راح ابحث عن مترجم علشان يقول لي

شنو الموضوع