LT5537 Input Matching Network

Hi all,

Following is the datasheet 9 page ~ @ LT5537,

Input Matching

The 1:4 input transformer can also be replaced with a narrow band discrete balun circuit using three components as shown in Figure 6.

Capacitors C11, C12 and inductor L1 form a tank circuit having a transformer-like function over a narrow bandwidth.

Table 2. Matching Network Component Values for 200MHz Center Frequency

Figure 6. Input Matching Network

How to caluculate the each component value, L1, C11,C12,R2 @ figure 6 ?

Input frequency is f = 400, 600, 800MHz, 1GHz.

Best regards,

sss

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  • +1
    •  Analog Employees 
    on Dec 15, 2019 9:15 PM

    Hi sss,

    The AD8310 has an almost identical reactive input matching circuit recommendation, and the datasheet has a good, complete explanation of how to calculate the input reactive discrete matching element components. Please take a look.

    Note that this discrete reactive matching circuit is by its nature narrow-band. The LT5537 circuit uses the additional (and optional) resistor R2 to widen the bandwidth, at the expense of sensitivity. So you should be able to match for either 400, 600, 800, or 1000 MHz, but not all 4 frequencies with the same circuit. 

Reply
  • +1
    •  Analog Employees 
    on Dec 15, 2019 9:15 PM

    Hi sss,

    The AD8310 has an almost identical reactive input matching circuit recommendation, and the datasheet has a good, complete explanation of how to calculate the input reactive discrete matching element components. Please take a look.

    Note that this discrete reactive matching circuit is by its nature narrow-band. The LT5537 circuit uses the additional (and optional) resistor R2 to widen the bandwidth, at the expense of sensitivity. So you should be able to match for either 400, 600, 800, or 1000 MHz, but not all 4 frequencies with the same circuit. 

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