The preface, with the gradual progress of the times, the cellular telephone has already joined technology of wireless communication such as WiFi, bluetooth and GPS to make it more and more complicated, interference problem that and the increasingly many wireless signal makes the design engineer make use of strong filter technique to avoid facing in the mobile phone design, especially global positioning system GPS Function.As to the synchronous global positioning system S-GPS, the receiving of GPS signal and conveyance of pronunciation or intelligence signal will concur in the mobile phone, and the receive path that may be let out to GPS of sending a message of pronunciation or data, cause the over load of the low-noise amplifier or rear end circuit, influence the degree of sensitivity of the receiver. This has brought strong challenge to design engineer of the mobile phone, because they must decide how to maintain the degree of sensitivity of the receiver under the faint GPS input signal, must face the pronunciation or interference that the data send a message at the same time. This needs one to have very good strong undesired signal to shield ability, and can offer GPS receiver forward end of low noise coefficient and faint GPS signal high gain. Integrate the low insertion loss and shield the ability FBAR electric-wave filter to the low-noise amplifier high The prefilter can be used for shielding the strong undesired signal and avoiding flowing into GPS receiver route, in accordance with Friis equation, the noise coefficient or insertion loss of the circuit of first step mainly depends on the noise coefficient of the receiver chain, so long as there is reasonable gain to noise temperature ratio in the circuit of rear. So, reach the above-mentioned goal, the design engineer must integrate one and have low insertion loss, high out-of-band inhibitory potencies and low-noise high gain and amplifier good in linear scale. A GPS forward end module products example with these characteristics come from Ann’s China Hi-Tech Avago Technologies The company, was made up by the chamber sound syntony electric-wave filter of the membrane and high electron mobility transistor low-noise amplifier of false shape of GaAs Enhanced Mode. FBAR is that one can offer the small-scale electric-wave filter of high q-factor, brings the proprietary technology of precipitous roll-off filtering and strong out-of-band inhibitory potencies, through the integrated filter, the module can shield the undesired signal close to 1.575GHz GPS signal, and maintain the low noise coefficient of the amplifier. As the example, the communication band of the satellite telephone uses 1.62GHz signal very close to GPS frequency, it if you can’t is it with filter capacity of the precipitous roll-off to so need by electric-wave filter on each, last signal but can attenuation band GPS signals inners prominent. Because the noise coefficient is usually decided by first step circuit of the receiver route, so, integrated low loss FBAR electric-wave filter of first step circuit in the module, add the intersection of GaAs and low-noise amplifier, can bring, have extremely low noise coefficient and high to lead outer shield best GPS receiver of ability subsequently. The radio frequency characteristic behaves Summarizing three fund in Table 1 has radio frequency characteristics not making GPS module up with the leading filtering, post-filtering summing amplifier that behave, first two piece module is at first step for circuit last one of FBAR electric-wave filters,and in after add by one of low-noise amplifiers, among them the second joins the extra POSTF electric-wave filter. The third module is the association that the low-noise amplifier added the POSTF electric-wave filter. Table 1 fit the intersection of China and Hi-Tech company make the intersection of GPS and the intersection of module and the intersection of radio frequency and characteristic of products up, display and simplify the functional block diagram with the intersection of electric-wave filter and summing amplifier. We can see by Table 1, the shielding ability to the undesired signal of first two pieces of module is much more outstanding, ALM-1912 and ALM-2712 are in the frequency band of the honeycomb, the intersection of PCS and frequency band and the intersection of WiFi and than at being in front of low-noise amplifier with electric-wave filter and ALM-1412 kind out-of-band the intersection of input and P1dB of frequency band, high out-of-band P1dB means the module can play normal operation in the strong undesired signal, will not cause the amplifier saturation. Measure and test is disposed In order to further understand the characteristics of these three different electric-wave filter summing amplifier composite modules behave in detail, the following comparison has revealed the shielding ability in case of undesired signal of three pieces of module in Table 1. Measurement goes on through monitoring the deterioration situation of the module under the special power level undesired signal of noise coefficient, use and close to GPS frequency, 1.62GHz undesired signal that may exert a largest influence on noise coefficient of GPS frequency while measuring. Fig. 2 carries on the metric test disposition. Fig. 1 GPS receiver Rx Simple functional block diagram of the forward end Fig. 2 measures test disposition that the undesired signal makes the deterioration situation of the noise coefficient. The filtering of the tandem connection trap filters and band-pass filters of Fig. 3 is responded to. The signal generator produced a lasting signal wave located in interference frequency, the power combiner combines undesired signal and noise source, then send the signal after making GPS module up to measure their own noise coefficients. Store first external pre-amplifier in amplify undesired signal until undesired signal and noise source make up, the noise coefficient analysis meter can be monitored and received the signal of the extremely low background noise, any extra noise from interference source is very important, so contained in the measurement of the noise coefficient. Lie in the intersection of GPS and high the intersection of background noise and interference source of frequency might cause the intersection of interference source and measurement but not the intersection of module and own measurement of noise coefficient of background noise. In order to guarantee the measurement of the noise coefficient will not include the extra background noise, use the undesired signal of filter attenuation GPS frequency while disposing in order to inhibit signal and noise. Just as discussing, make tests correctly and accurately that there must be high inhibitory potencies while going on ago. We can see by Fig. 2, interfering with the signal source to arrange for the band-pass filter can filtrate the harmonic wave of the undesired signalling. In addition, the background noise that two trap filters can inhibit the undesired signal of GPS frequency put behind the band-pass filter. Fig. 3 reveals the frequency response of two tandem connection trap filters and band-pass filters, tandem connection electric-wave filter offers decay and 1.62GHz of 100dB to interfere with the low loss of the signal frequency in 1.575GHz. As to examining the device, i.e. GPS mould The test disposition of a piece of rear, arranging can shield the strong undesired signal and avoid entering the analysis meter of the noise coefficient in the forward GPS band-pass filter of analysis meter of the noise coefficient, help analysis meter avoid, receive strong undesired signal, influence but over load. The measuring result discusses Fig. 4 has revealed the deterioration situation that three pieces of module make the noise coefficient in the strong 1.62GHz undesired signal, mainly regard there is no noise coefficient of every module of undesired signalling as and consult, the test disposition in Fig. 2 of the measuring result. The noise coefficient deterioration of Fig. 4, to the relation that interferes with signal intensity As to ALM-1412 module with prefilter in the circuit of first step, reach in the undesired signal – the deterioration of the noise coefficient exceeds 1dB before 10dBm power level, but ALM-1912 and ALM-2712 module was not influenced in the noise coefficient, even does not have when the power level of the undesired signal reaches 20dBm. Very obvious, GPS module with prefilter has better inhibitory potencies to the strong undesired signal, in this example, measure the data display, compared with ALM-1412 module with electric-wave filter in front of the amplifier, with prefilter ALM-1912 and the intersection of ALM-2712 and to at the to resist ability take kind strong undesired signal module. Conclusion Generally speaking, may be offered and confronted with each other the noise coefficient characteristic with better undesired signal to behave in the intersection of the circuit of first step and integrated the intersection of FBAR and electric-wave filter, FBAR low to insert, consume until the intersection of amplifier and influence of noise coefficient minimum in electric-wave filter, so, there is low GPS amplifier module which inserted consuming and high out-of-band inhibitory potencies FABR prefilter that has offered the optimum alternatives of chains of GPS receiver, another extra advantage is, all parts can save space and design deadline of circuit board while capsulating to integrate to the small-scale module.
Use the prefilter LNA module to improve the receiver of the synchronous operation GPS
Posted on September 21, 2013 by admin
Categories: Technology Application | Tags: converter, Discrete device, GPS, LNA module, prefilter, stabilizator
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