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Hi All,

I am planning to use the ADL5243 amplifier in DSAIN-AMP2OUT configuration in frequency ranging between 450MHz and 650MHz and a centre frequency of 500MHz and wish to get 23dbm output across these frequencies for a 50 ohm load. I want to implement this in Microstrip transmission line in FR4 ( as the frequency is not very high, i dont want to invest on cpw or rogers3003 material).

1. Can you please tell me if my implementation of microstrip transmission line is correct or does the IC warrant a high frequency design for such frequencies (should i build the PCB with rogers3003 or cpw)

2. Can you please tell me the matching network for DSAIN-AMP2OUT configuration for such frequencies. (please do specify components value and the location(distance) where it has to sit from the IC)

3. What is the cap driving capacitance of the amp2?

4. Can you suggest a good material where i can study thumb rules for high frequency PCB layout.

Please reply as soon as possible as my project is currently in the critical path. Thanks in advance

Thanks and Regards,

Nishanth A B

  • HI Nishanth,

    Sorry for the delay in replying.

    It is highly recommended to refer the evaluation board layout for the optimal and stable performance of each block as well as for the improvement of thermal efficiency.

    All RF traces on the evaluation board have a characteristic impedance of 50 Ω and are fabricated from Rogers3003 material. The traces are CPWG with a width of 25 mils, spacing of 20 mils, and dielectric thickness of 10 mils. The input and output to the DSA and amplifier should be ac-coupled with capacitors of an appropriate value to ensure broadband performance.

    The AMP2 input and output of the ADL5243 can be matched to 50 Ω with two or three external components and the microstrip line used as an inductor. Table 8 lists the required matching components values. All capacitors are Murata GRM155 series (0402 size), and Inductor L2 is a CoilcraftR 0603CS series (0603 size). For all frequency bands, the placement of Capacitors C22,  C26, and C28 is critical.

    Table 9  on Datasheet lists the recommended component spacing of C22, C26, and C28 for the various frequencies. The placement of R12 and

    C27 is fixed for the matching network on evaluation board and the spacing is 153 mils and 25 mils respectively. The component spacing is referenced from the center of the component to the edge of the package. Figure 61 to Figure 69 show the graphical representation of the matching network. It is recommended to configure a RC feedback network and bias the AMP2 input through external R for optimal performance at frequency bands less than 500 MHz as shown at Figure 61 and Figure 62. In this case, VBIAS pin must be left open.

    For your frequency band of interest 450MHZ refer Table 8 & Table 9 and Fig 62 on the Datasheet.

    For matching network, for 500MHz center frequency you can start with 450Mhz matching N/W as a reference and then tune the components to get right match at the output for a 23dBm gain.

    Across the frequency range from 450 to 650Mhz pick the frequencies that are closer to the frequencies listed in Table 8.. for ex Use 748Mhz as the starting point and then tune the components to match the N/W for 650Mhz. You can use ADS simulation for this exercise..

    Would recommend simulating your implementation of Microstrip transmission line in FR4  in ADS software to see if it meets your system requirements.. As the recommended implementation is CPWG with a width of 25mil spacing of 20mils and dielectric thickness of 10mils and fabricated on Rogers 3003 material.

    The cap driving capacitance of AMP2 for 450Mhz is shown in Fig 62 of the datasheet and it is frequency dependent. Refer to Table 8 & 9 in the DS along with Figure 61 to Figure 69 showing the graphical representation of the matching network. 

    Warm Regards,