AN4271 STMICROELECTRONICS | Alldatasheet
Document overview
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Technical content
Datasheet sections
- 1 Application circuit
- 2 Transmitter parameters
- 2.1 Adjacent channel power
- 2.2 Modulation bandwidth
- 2.3 Unwanted emissions in the spurious domain
- 3 Receiver parameters
- 3.1 Receiver sensitivity
- 3.2 Blocking
- 3.3 Receiver spurious radiation
- 4 Measuring equipment
- 5 Reference
- 6 Revision history
Using the SPIRIT1 transceiver with range extender under EN 300 220 at 868 MHz Placido De Vita Introduction The SPIRIT1 is a very low power RF transceiver, intended for RF wireless applications in the sub-1 GHz band. It is designed to operate both in the license-free ISM and SRD frequency bands at 169, 315, 433, 868 and 915 MHz. This application note outlines the expected performance when using the SPIRIT1 under EN defined for specific applications, the maximum radiated power is +27 dBm (500 mW), and the defined channel spacing is < 25 kHz with 10% duty cycle. The whole stated frequency band may also be used as 1 wide-band channel for high speed data transmission. For details on the regulatory limits in the 869.400 - 869.650 MHz SRD frequency bands, please refer to ETSI EN 300 220-1 v2.4.1 [2] and ERC Recommendation 70-03 [3]. These
1 Application circuit
Figure 1 shows the SPIRIT1 with range extender application board photo. The application is made up of 2 boards: a daughterboard and a motherboard. The daughterboard holds the SPIRIT1 with the circuits necessary for its function. For correct operation, the daughterboard must be plugged into the motherboard (see Figure 2) by two header 5x2 connectors (J6 and J7). The motherboard is equipped with an STM32L152VBT6 microcontroller to correctly program the transceiver. The microcontroller is programmed with firmware developed for the SPIRIT1 application. A graphical user interface (GUI) has been developed for programming of the SPIRIT1. The daughterboard includes a 50 MHz crystal to provide the correct oscillator to the SPIRIT1. The SPIRIT1 has an internal SMPS that drastically reduces power consumption, making the SPIRIT1 the best-in-class for the application on this bandwidth. The SMPS is fed from the battery (1.8 V to 3.6 V) and provides a programmable voltage (1.4 V typ) to the device. An SMA connector is provided to connect the board to the antenna or to instrumentation in order to verify correct functionality and confirm the ETSI standard required. A few of passive devices (inductors and capacitors) are used as matching/filtering for the power amplifier (PA) and balun network for the receiver. A SAW filter is recommended in the TX path to attenuate the spurious emissions above the carrier frequency, which would otherwise violate spurious emissions limits under ETSI 300 220 [2]. The same SAW filter is provided in the RX path because, due the proximity of the GSM band, the receiver can be saturated in an application environment. This SAW filter can be bypassed using a short R1 resistor. The SAW filter used is a Tai-Saw Technology CO., LTD. TA0801 868 MHz SAW filter [5]. An external FEM (front-end module) is used to improve the output power at the +27 dBm requested. The FEM utilized is a Skyworks SE2435L [6]. The device includes a power amplifier (PA) capable of about +27 dBm of transmitted output power. The receive channel consists of an integrated LNA (low noise amplifier) with programmable bypass. An integrated antenna switch, which provides an insertion loss of approximately 0.8 dB, separates the TX and RX paths.
Figure 3. Daughterboard circuit schematic (1 of 2)
Figure 4. Daughterboard circuit schematic (2 of 2)
AN4271 Transmitter parameters
2 Transmitter parameters
All the measurements reported here have been measured with the following parameters: TC = 25 °C, VDD = 3.3 V, f = 869.500 MHz. The adjacent channel power, modulation bandwidth and unwanted emissions in the spurious domain measurements are also reported. The measurements are performed in accordance with EN 300 220 v1 [2].
2.1 Adjacent channel power
The adjacent channel power (ACP) is defined as the amount of the modulated RF signal power which falls within a given adjacent channel. This power is the sum of the mean power produced by the modulation, hum and noise of the transmitter. This measurement is applicable only to narrow band systems. This test measures the power transmitted on the adjacent channel during continuous modulation. The ACP is measured with a spectrum analyzer conforming to the requirements given in the EN 300 220-1 v2.4.1 (2012-01) [2] annex C. In this application note, the ACP measured with 12.5 kHz channel spacing is investigated. For this measurement, the integrated bandwidth of the adjacent channel is 8.5 kHz. The ETSI limits for the ACP is 10 μW (-20 dBm) for channel separation of 12.5 kHz. Figure 5 illustrates the measured ACP at the 869.5 MHz center frequency. The data rate is set to 2.4 kbps, the frequency deviation is set to 2.4 kHz, and the modulation is set to Gaussian FSK (GFSK) with a BT = 0.5. The output power integrated around the carrier is 27 dBm in 8.5 kHz bandwidth. With this power the ACP is -30 dBm, which is 10 dB better than the ETSI limit. The SPIRIT1 is fully compliant with the ETSI transmitter adjacent channel power requirements, with margin.
Figure 5. adjacent power measurement, 12.5 kHz narrow band channel spacing
2.2 Modulation bandwidth
appropriate emissions level and the frequency error or drift under extreme test conditions. is not included in this report. so the measurement is performed for a case with a channel bandwidth greater than 25 kHz. integration at the different offset regions.
2.3 Unwanted emissions in the spurious domain
[2]. In the two graphs, the mask requirement from ETSI is reported also. Figure 8. Unwanted spurious emission below 1 GHz
Figure 9. Unwanted spurious emission over 1 GHz
Receiver parameters AN4271
3 Receiver parameters
All the measurement reported here are measured with the following parameters: TC = 25 °C, VDD = 3.3 V, f = 869.500 MHz. The family of short range radio devices is divided into three receiver categories, each having a set of relevant receiver requirements and minimum performance criteria. The set of receiver requirements depends on the choice of receiver category by the equipment provider. The SPIRIT1 is a transceiver that meets the requirements of receiver category 2, which means medium reliable SRD communication media that can cause inconvenience to persons, which cannot simply be overcome by other means. The main parameters that have to be measured for category 2 devices are sensitivity, blocking and receiver spurious radiation.
3.1 Receiver sensitivity
Receiver sensitivity is the minimum level of the signal at receiver input, produced by a carrier at the nominal frequency of the receiver, modulated with the normal test signal modulation, which produces performance of a bit error rate (BER) of 10-2 without correction. Under normal test conditions, the value of the typical usable sensitivity for 25 kHz channel spacing equipment with a 16 kHz bandwidth shall not exceed -107 dBm. If the RX bandwidth is not 16 kHz, the sensitivity limit is modified according to the following formula: Equation 1 The measurement is performed using an RF signal source generator centered at the same receiver frequency as the desired modulation signal. The demodulated data and clock are taken from the SPIRIT1 receiver and sent to the same generator to do the BER measurement. The generator signal level is reduced until a BER of 1% is obtained. To reduce power consumption, an internal SMPS is integrated in the SPIRIT1. Figure 10 demonstrates the ETSI 1% BER sensitivity limit (red line) and the SPIRIT1 sensitivity for different data rate. This application note outlines the expected performance when using the SPIRIT1 under EN 300 220-1 (v2.4.1, 2012-01) [2] in the 869.400 - 869.650 MHz band, with the channel lower than 25 kHz, or with a single channel of the 250 kHz band. Just to show the real performance of the application, different channel spacings are shown. The test conditions are: GFSK (BT = 0.5) modulation with 2.4 kHz frequency deviation and 8 kHz channel bandwidth for the 2.4 kbps data rate, GFSK (BT = 0.5) modulation with 1.2 kHz frequency deviation and 8 kHz channel bandwidth for the 4.8 kbps data rate, GFSK (BT = 1) modulation with 20 kHz frequency deviation and 250 kHz channel bandwidth for the 38.4 kbps data rate. The sensitivity is also measured with a PER of 1%. The SPIRIT1 is fully compliant with ETSI class 2 receiver sensitivity requirements, with a large margin. Sp[dBm] 10log BW[kHz] 107–=
Figure 10. Sensitivity vs. data rate with 1% BER
3.2 Blocking
degradation of 1% is obtained. data rates; Figure 12 shows the blocking curve with 38.4 kbps data rate. requirements, with a large margin.
Figure 11. RX blocking vs. CW interferer offset with 1% BER, 1.2 kbps data rate Figure 12. RX blocking vs. CW interferer offset with 1% BER, 500 kbps data rate
3.3 Receiver spurious radiation
required by ETSI [2]. In the two graphs, the mask required by ETSI is reported also. The receiver spurious radiation of the SPIRIT1 complies with ETSI [2] sub-clause 8.6. Figure 13. Receiver spurious emission below 1 GHz
Figure 14. Receiver spurious emission over 1 GHz
4 Measuring equipment
The following equipment was used to perform the measurements. Table 1. Measuring equipment
5 Reference
- STMicroelectronics SPIRIT1 datasheet 2. ETSI EN300 220 V2.4.1: “Electromagnetic compatibility and Radio spectrum Matters (ERM); Short Range Devices (SRD); Radio equipment to be used in the 25 MHz to
1000 MHz frequency range with power levels ranging up to 500 mW”
- CEPT/ERC/Recommendation 70-03: “Relating to the use of Short Range Devices (SRD)” 4. CEN/TC prEN 13757-4:2011.10: “Communication systems for meters and remote reading of meters - Part 4: Wireless meter readout (Radio meter reading for operating in SRD bands)” 5. TAI-SAW Technology CO., LTD. TA0801A “SAW Filter 868 MHz” datasheet 6. Skyworks “SE2435L: 960 - 930 MHz High Power RF Front End Module” datasheet
6 Revision history
Table 2. Document revision history 24-Oct-2013 1 Initial release.