What is the difference between a modulator and a vector modulator?

The circuit description for the quadrature modulators seems to be the same for the vector modulators. As an example compare the AD8349 modulator with the AD8341 vector modulator. Both split the RF input with a 90 degree difference, then independently vary the amplitude of the two split paths, then recombine the two split paths.

Can I use them interchangeably or am I missing something?

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    •  Analog Employees 
    on Mar 19, 2013 8:21 PM

    IQ Modulators are generally used to modulate a sine wave tone. Vector modulators are used to adjust the gain and phase of a signal that may already be modulated. So they are functionaly very similar but are used differently.

    An IQ Modulator has high gain in the LO path (e.g. 10-20 dB). The LO is generally a saturated square wave by the time it hits the two internal mixers. So a 1 dB change in the LO level results in no change in the RF output power.

    In a vector modulator, the LO path (which is called RFIP and RFIM in AD8340 and AD8341) has significantly less gain (e.g. 0 dB to -5 dB) and is intended to be operated with a linear power drive. So a 1 dB change in RFIP/RFIM  results in a 1 dB change at RFOP/RFOM.

    If you back off the LO power level to an IQ Modulator, at some point the LO-to-RF path will become linear. So you can use an IQ Mod as a Vector Modulator with a low enough RF input signal.

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    •  Analog Employees 
    on Aug 2, 2018 4:48 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin