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Achieve high input IP3 mixer Rugged VHF receivers

 

[ REVIEW ] occupies 30MHz to 300MHz very high frequency (VHF) band more and more applications . Television and radio broadcasting , amateur radio and navigation controls , such as just a few examples. The new RF component development is much higher for voice and data communications system for the band. In order to meet the stringent performance requirements of the next generation of radio , you need to make significant progress in terms of circuit technology and manufacturing processes .

Introduction

Occupy a very high frequency 30MHz to 300MHz (VHF) band more and more applications . Television and radio broadcasting , amateur radio and navigation controls , such as just a few examples. The new RF component development is much higher for voice and data communications system for the band. In order to meet the stringent performance requirements of the next generation of radio , you need to make significant progress in terms of circuit technology and manufacturing processes . The application of these techniques to a low frequency design can significantly improve performance.

LTC ® 5567 is a broadband mixer , designed for high performance in the 300MHz to 4GHz band designed and optimized . In order to create a very compact circuit implementation , LTC5567 built integrated RF and LO transformer. In the frequency range of its provisions , the input IP3 linearity performance LTC5567 is very good , reaching 30dBm. To a lower frequency transformer is required to keep the built- linearity and conversion gain. Due to the linearity of threshold levels so high , so whom change mixer circuit design and performance of the lower VHF frequencies to characterize the calibration is worth it. And demonstrate the performance of the test.

Impedance matching design

Figure 1 shows a use of the impedance matching design LTC5567 . Table 1 lists the matching at the input port extended to cases below 300MHz ( lowest to 150MHz) still achieve excellent performance under the design value . Further , the test results are also provided .

 

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Figure 2 shows the relationship between gain and input LTC5567 IP3 mixer input frequency. When the input frequency is close to 150MHz, the mixer linearity performance improvement. Inputs, LO, and the output port return loss measurement results are shown in Figure 3, Figure 4 and Figure 5. Compared to the higher input frequencies in the VHF range the overall performance is maintained. Thus, when used in radio design, its high conversion gain and IP3 maximum dynamic range can be generated. A high dynamic range to maximize the adjacent channel interference suppression, thereby improving selectivity. Although the LTC5567 can operate (in this case the conversion gain drops) at less than 150MHz input frequency, but this is not recommended, because the internal transformer would be detrimental.

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