Hi Everyone,

I want to use ADL6501 to achieve maximum gain. In order to get the mentioned gain in the datasheet at my frequency band of interest (1520 - 1820 MHz), the input impedance of amplifier should be matched to 50 ohms which is my system characteristic impedance.

Could you please give a brief explanation on which data to be used as S11 to be matched for input impedance to achieve maximum gain?


  • 0
    •  Analog Employees 
    on Nov 19, 2012 8:41 PM

    I think that it will be difficult to get a lot more gain out of ADL5602 in the 1520-1820 MHz range. From the s-parameter plot (Figure 5 in Rev. 0 datasheet), you can see that the input and output return loss in this frequency range is the 11-13 dB range. So, for example, if you could improve the S11 then there will be more power delivered to the device which will give you more output power. However, I don't think that the benefit will be large because the input return loss is already quite good. If the return loss is -12 dB, that means that one sixteenth of the power incident on the amplifier's input is being reflected back. So even if you could reduce the input return loss to minus infinity, the power delivered to the load would only increase by about 0.25 dB.

    If you do want to try this, I would suggest an experimental approach rather than an analytical approach. You can try to add shunt matching components at the input and output. Basically you put the amplifier eval board on to a network analyzer and then experiment with cap sizes and locations, much in the same way as the matching of a driver amplifier is optimized (see ADL5320 datasheet to get more insight on this).

  • Dear Enash,

    Thanks for your reply.

    My question is if I use ADL5602 in 1520-1820 MHZ, without any matching how much would be the gain, S11,S22 and other parameters like OIP3, P1dB and NF?

    I mean the parameters given in Table 1 of datasheet are with optimum matching; So for my case since I don't have the evaluation board, what should I consider the parameters without any matching (Since its mentioned that input/output impedances are 50 ohms for the amplifier)

    Thanks a lot

  • 0
    •  Analog Employees 
    on Nov 19, 2012 9:14 PM

    I don't fully get the question but this statement may help. If you drive the ADL5602 from a 50 ohm source and load the output with 50 ohms you will get the performance specified in the datasheet without any additional matching components (apart from the ac-coupling capacitors which are set large enough  so that their impedance is negligible; so they do not count as being matching components).

    If your source and load impedance are not 50 ohms, then you need to try and match them to 50 ohms to get the specified performance from the ADL5602.  If you know the s-parameters of the source and load, you could put these into a simulator with the s-parameters of ADL5602 and this should give you a feel for how much power you will lose as a result of the mismatch.

  • I read in the datasheet that input/output impedances are matched to 50 ohms for ADL5602 in all of its frequency range of operation. Table 1 in the datasheet is showing each parameter such as gain, OIP3, etc at different operating frequencies.

    But I got confused when I saw Table 2 which is showing the S-parameters at different frequencies; So if the gain of device is the shown values at table 1, what is the purpose of S-parameters given in Table 2?

    Sorry for asking a lot of questions since its my first design in RF field.


  • 0
    •  Analog Employees 
    on Nov 19, 2012 11:33 PM

    The gain numbers in Table 1 do indeed match closely with the S21 values shown in Table 2 at the coresponding frequencies. For example, Table 1 says that the gain at 700 MHz is typically 20.2 dB and in Table 2, S21 at 700 MHz is listed as 20.42.  The s-parameter gives additional information about the angular relationship between input and output level as well as the S11 and S22. S11 and S22 are an indication of how the input and output impedances deviate from their ideal value of 50 ohms (if the input and output impedances were exactly 50 ohms, S11 and S22 in Table 2 would show as -Infinity dB.