The AD833x devices are essentially configured as an LNA followed by a resistor ladder variable attenuator (with added circuitry to make a 48dB VGA), and lastly a post-amp. There is direct access to the connection between the LNA and the VGA at the pins of the device. One could choose to directly connect these pins, such that the input range of the LNA is defined as 500mVpp, which after the 19dB LNA gain will supply roughly 4.5Vpp at the VGA input.
My question is, if I add more gain between the LNA and VGA such that the input range is still limited to 500mVpp but I go over 4.5Vpp at the output of my external amplifier, can the resistor ladder in the VGA handle overvolting? For example, assume I add 15dB of gain between the LNA and the VGA, and I supply a 500mVpp signal at the input of the LNA. There should be 4.5Vpp at the LOP/LON pins on the AD833x, and the output of my 15dB intermediate amp will be 25Vpp (let's just assume the worst-case). If the attenuator is set to 48dB, the output of the VGA should be 0.1Vpp followed by 1.13Vpp after the post-amp. If the VGA is indeed as ideal as the simplified diagram, then I should only have to worry about power dissipation in the resistor ladder? I am wondering if there are voltage limits to the switches that adjust the resistor adder in 6dB steps, and also the interpolation circuits. I do not believe there is much info in the datasheet about these parameters. Does anyone know more about the limitations of the VGA?
Thanks.
