Measures and Influence of a Baw Filter on Digital Radio-Communications Signals

This work concerns the measurements of a Bulk Acoustic Waves (BAW) emission filter S parameters and compare with prototypes simulated types. Thanks to HP-ADS, a co-simulation of filters’ characteristics in a digital radio-communication chain is performed. Four cases of modulation schemes are studied in order to illustrate the impact of the spectral occupation of the modulated signal. Results of simulations and co-simulation are given in terms of Error Vector Measurements to be useful for a general sensibility analysis of 4/3 Generation (G.) emitters (wideband QAM and OFDM signals) Keywords— RF architectures, BAW filters. I. FILTER MEASUREMENTS AND COMPARISON URRENTLY, BAW filters are supposed to be used for 4/3 G. standards and beyond as emission filters. They can offer a good selectivity and reduce the total size of the transmitter [1][2][3][4][5]. The effect of electrical parameters of such filters in a radio-communication chain is not accurately quantified yet. Amplitude, phase and group delay variations are a key point to study in order to evaluate the influence on the signal quality. Quality decrease that will occur is to be compared with sensibility analysis of emitter architectures for these types of signals [6]. Specifications for these applications are given here by the impact of the filter on the EVM (Error Vector Magnitude). This paper is to characterize the influence of a given BAW filter [1] response when it is used in a radiocommunication link for wideband complex modulation.First, the comparison with prototype filters is presented and second is simulations of four modulations cases, representing some of 4/3 G. signals. The emitted power dependency on the filter response is considered here and approximated by preliminary measurements. Principle of the high signals analysis is exposed at the end of simulations results. In order to compare with prototype filters, the BAW filter, an Agilent ACPF 7001 represented in figure 1, is measured thanks to a VNA (Vector Network Analyzer).S parameters of the filter are measured from 1.7 to 2.1 GHz (UMTS/LTE bands) as it can be seen on figure 2. The pass-band of the ACPF is 1.84 to 1.91 GHz. Return loss measurement corresponds well to datasheet specifications. Also the attenuation in the stop-band is in A. Diet is with L2S-DRE UMR8506 (Université Paris Sud-11, CNRS, Supelec) Supelec, Plateau du Moulon F-91192 Gif Sur Yvette, France. [email protected]. M. Villegas and G. Baudoin are with ESYCOM EA2552 (groupe ESIEE Paris Université Paris-Est Marne la Vallé, CNAM) groupe ESIEE, bvd Blaise Pascal, 93162 Noisy le Grand, France. [email protected], [email protected]. the range of 30 dB. The phase response of figure 1 is not very linear and figure 4 shows a maximum delay variation of 30 nano-secondes (nsec) on the whole bandwidth (worse case). Three filter types are considered here to make a comparison in terms of amplitude and/or group delay response: Butterworth (N=12, 70 MHz passband), Chebychev (N=7, 80 MHz passband) and Cauer (N=3, 62 MHZ passband). Common parameters used in ADS simulator are an Insertion Loss (IL) of 2.2 dB and a center frequency of 1.88 GHz to fit the filter measurements. First is the comparison in terms of amplitude variation, as shown on figures 2 and 3. As we can see on a wide frequency range, the Cauer type filter seems to be the best approximation of the measured BAW filter response, considering only the |S21| parameter. 1.75 1.80 1.85 1.90 1.95 2.00 2.05 1.70 2.10 -50 -30 -10