Hi All,
So I'm trying to build a passive active network. It's so my antenna can operate in the passive mode once the batteries for my amplifier run out of juice.
I'm using the MAX8211 voltage monitor to look at my battery and output a HIGH when the battery is a-ok and a LOW once the voltage drops below a certain threshold voltage, as set by the bias resistors on the MAX8211 chip.
So the idea is to pass my AC signal from my antenna straight to the output when the voltage monitor goes LOW and pass it to the amplifier when it's HIGH.
I thought I may be able to do this with a transistor switching network. However, I'm not too good with transistor networks, so I figured I would ask for some help.
My idea is to use a combination of NPN and PNP switches. I figure I would have a NPN that would be operating in the saturation region (Switch ON, Vbe > .7V, etc.) when the output of the voltage monitor is HIGH and operating in the cutoff region when the output is LOW. This logic would be inverted for the PNP.
In summary:
IF output of MAX8211 Voltage Regulator HIGH:
NPN acts as closed switch
PNP acts as open switch
IF output of MAX8211 Voltage Regulator LOW:
NPN acts as open switch
PNP acts as closed switch
However, I think I'm biasing the transistors wrong. I attempt to run a simulation in LTSPICE, with the output of the MAX8211 simulated as just a simple DC supply (5V for HIGH, 1V for LOW) and while I'm able to get the active track to be fully on at 5V with some minimal attenuation and fully off at 1V, the passive track doesn't seem to vary in either the 5V or 1V configuration.
I've attached a picture of the LTspice schematic I'm using. The PNP transistor I'm using is: http://www.fairchildsemi.com/ds/MM/MMBTH81.pdf
And the NPN is:
http://www.nxp.com/documents/data_sheet/PRF947.pdf
My input signal frequency varies from 50 MHz - 500 MHz and is on the order of microvolts.
I thought that I might need a different bias network (R1/R2) for the NPN and the PNP, but when I tried that my active network stopped working so I went back to the single bias network.
I can provide the LTspice .asc and .lib files if necessary.
Sorry for the long post and thank you in advance for your help!
So I'm trying to build a passive active network. It's so my antenna can operate in the passive mode once the batteries for my amplifier run out of juice.
I'm using the MAX8211 voltage monitor to look at my battery and output a HIGH when the battery is a-ok and a LOW once the voltage drops below a certain threshold voltage, as set by the bias resistors on the MAX8211 chip.
So the idea is to pass my AC signal from my antenna straight to the output when the voltage monitor goes LOW and pass it to the amplifier when it's HIGH.
I thought I may be able to do this with a transistor switching network. However, I'm not too good with transistor networks, so I figured I would ask for some help.
My idea is to use a combination of NPN and PNP switches. I figure I would have a NPN that would be operating in the saturation region (Switch ON, Vbe > .7V, etc.) when the output of the voltage monitor is HIGH and operating in the cutoff region when the output is LOW. This logic would be inverted for the PNP.
In summary:
IF output of MAX8211 Voltage Regulator HIGH:
NPN acts as closed switch
PNP acts as open switch
IF output of MAX8211 Voltage Regulator LOW:
NPN acts as open switch
PNP acts as closed switch
However, I think I'm biasing the transistors wrong. I attempt to run a simulation in LTSPICE, with the output of the MAX8211 simulated as just a simple DC supply (5V for HIGH, 1V for LOW) and while I'm able to get the active track to be fully on at 5V with some minimal attenuation and fully off at 1V, the passive track doesn't seem to vary in either the 5V or 1V configuration.
I've attached a picture of the LTspice schematic I'm using. The PNP transistor I'm using is: http://www.fairchildsemi.com/ds/MM/MMBTH81.pdf
And the NPN is:
http://www.nxp.com/documents/data_sheet/PRF947.pdf
My input signal frequency varies from 50 MHz - 500 MHz and is on the order of microvolts.
I thought that I might need a different bias network (R1/R2) for the NPN and the PNP, but when I tried that my active network stopped working so I went back to the single bias network.
I can provide the LTspice .asc and .lib files if necessary.
Sorry for the long post and thank you in advance for your help!
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