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Enable/Disable HMC8413

Category: Hardware
Product Number: HMC8413
Software Version: n/a

Hello AD,

I would like to be able to enable/disable an individual HMC8413 RF amplifier without changing its RF characteristics while introducing zero (or an absolute minimum) of added noise into my signal path. I have come up with the scheme shown below and want to run it past the experts at AD to see if they think it will work.

In words what I am doing is placing a SPST analog switch (ADG801) in series with the Rbias resistor that is nominally 787 ohms. The switch is controlled with a CMOS logic level and is assumed to be operated in an ON/OFF - very, very low bandwidth - configuration. When the switch is ON it adds less than an ohm of resistance to Rbias and the HMC8413 should operate normally with a 95 mA DC bias current from a 5V supply. When the switch is OFF it should effectively raise the Rbias value to several mega-ohms thus reducing the amplifier bias current to something less than 20 mA (or ideally 0) and effectively disabling it's operation and hence current consumption, heating, etc. When the amplifier is disabled there will be no RF input signal and its output is ignored.

Schematically it looks like this:

My questions are:

1. Will this work in Enabling/Disabling the amplifier?

2. Do you see any adverse effects to the noise performance of the amplifier (noise figure, OIP3) when the amplifier is enabled?

Thank you,

Tony

Parents
  • This will work but I would recommend using a single pole double throw switch (SPDT) so that RBIAS is grounded when you want to turn the part off. There is a circuit in the ADL8107 datasheet that you can copy. See Figures 83 and 84. The input and output coupling caps and the RLC network will affect the turn on and turn off time. If you need to turn on and off very fast, you can reduce the values of these components. With the default component values, expect the circuit to turn on an off in 60 to 100 us. 

  • Hi enash, 

    From the datasheet of ADL8107, it seeme like the amplifer turn-on turn off time is ard 100ns? (can I chk if I had read the graph correctly?) Are we expecting simiar switching time for HMC8413? 

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