Design of duplex filter based on MAX3580 input
The MAX3580 is a direct conversion tuner for Digital Video Terrestrial Broadcasting (DVB-T). This article discusses the case of adding a duplex filter to the input of the MAX3580 to improve the second-order input intercept point (IIP2). The integrated input switch allows the MAX3580 to select one of the duplex filters for filtering to pass signals in the desired band while suppressing signals in the interfering band. This feature makes the duplex filter especially suitable for DVB-T applications because the frequency range specified by DVB-T includes two separate frequency bands. Since the two bands are independent of each other, when it is necessary to suppress the signal of one of the bands, only one of the duplex filters is selected. By suppressing the interference band signal, the second-order distortion indicator is improved because the factor causing the second-order distortion comes from the interference band. working principle The fully integrated direct conversion tuner covers the input frequency range of the MAX3580 from 170MHz to 230MHz (VHF-III) and 470MHz to 878MHz (UHF). The MAX3580 integrates an RF input switch and multi-band tracking filter to provide a low-power tuner solution that eliminates the cost and power issues of a secondary conversion solution. This zero-IF architecture eliminates all of the SAW filters and directly outputs the baseband I/Q signals. Duplex filter Since two separate frequency bands (VHF and UHF) are used in DVB-T applications, a duplex filter can be used in conjunction with the input switches of the MAX3580 to improve the performance of the second-order input intercept point (IIP2) and suppress Strong out-of-band signal. The integrated input switch is shown in Figure 1. Figure 2 and Table 1 are the recommended duplex filters. Both inputs of the duplex filter are connected to the antenna. The output of the VHF filter is connected to the RFIN2 pin of the MAX3580, and the output of the UHF filter is connected to the RFIN pin of the MAX3580. Figure 1. Functional block diagram of the MAX3580 Figure 2. Schematic of the MAX3580 duplex filter When the receiver is tuned to the VHF band, the input switch setting receives the signal through the low-pass filter, allowing the signal in the VHF band to pass while suppressing the signal in the UHF band. Similarly, when the receiver is tuned to the UHF band, the input switch is set to receive the signal through the high-pass filter to pass the UHF band signal while suppressing the VHF band signal. Figure 3 shows the frequency response curves of the two filters obtained by measuring the MAX3580 evaluation board (rev 1). Figure 3. Suppression and insertion loss of the duplex filter The duplex filter is used with the MAX3580. The isolation of the interference band measured on the same evaluation board is shown in Figure 4. When tuned to the VHF band, the signal in the UHF band is attenuated by 15dB (typ); when tuned to the UHF band, the signal in the VHF band is attenuated by at least 32dB. Figure 4. Isolation between bands when the duplex filter is used with the MAX3580 This proprietary approach increases the IIP2 metric while minimizing the impact on the overall noise figure. The improvement of the IIP2 in the VHF band is attributed to the attenuation of the UHF band, which produces AB distortion in the VHF band. Similarly, the improvement in the UHF band IIP2 is attributed to the attenuation of the VHF band signal, since the VHF band produces A+B and AB distortion in the UHF band. It can be seen from Table 2 that the duplex filtering scheme improves the IIP2 by more than 30 dB for the selected input frequency and LO, and the noise figure decreases by less than 0.8 dB. It can be seen from Figure 4 that IIP2 is improved in other ways, and IIP2 is improved by isolation of the out-of-band input signal. When both input frequencies are outside the band, the sum of the attenuation of the two is the improvement of IIP2. Therefore, when the input frequency is 707.5MHz, 878MHz, and the LO frequency is 170MHz, IIP2 can still increase by 25dB. Npf960 Battery,Sony Psp Battery,Sony Npf970 Battery,Sony Game Player Battery Shenzhen Sunwind Energy Tech Co.,Ltd , https://www.sunwindbatterylm.com
