☑ Diode Mixer Termination

Regardless of whether the dbm is based on schottly sic diodes fets or analog switches the provision of the correct termination impedance over. High quality high speed diodes which will take the necessary saturating current and large reverse voltages across the non conducting diodes are used.

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The diode mixer has a dc bias that can be raised to unbalance it and allow cw operation more about it later the mixer is fed from clock2 of the si5351 through an attenuation pad.

Diode mixer termination. This is primarily because the power supplied to the mixer lo port is usually large enough to violate the small signal approximation. Here the input is couplet via an input dividing filter and the output is correct terminated via a 50 ohm amplifier to the the spectrum analyser and the ip3 is still 275sbm. Iip3 db lo dbm 9db because the lo voltage is applied from the gate to the source drain and the signal flows from source to drain there is an independence that allows fets to have a higher iip3 for a given lo drive than a diode mixer.

Reactance associated with the diode junction and package are ignored to simplify the analysis. All types of mixers need some form of defined termination but in passive double balanced mixers dbm this is particularly important. Ensure the ports are accurately matched.

Diode double balanced mixers are termination impedance sensitive. They must be terminated with the correct resistive load or source impedance normally 50 ohms. Here the mixer is terminated in a series resonnance circuit on the input and a narrowband 50ohm termination with xtal filter on the output.

This is better as the amplifier gain may be used to offset the mixer insertion loss. Diodes need to be well matched. An alternative is to use a wide band low noise class a amplifier with an input impedance of 50 ohms.

The gate to channel impedance. In a well designed passive diode mixer should get. Im reading about the design of double balanced diode mixers from various sources.

Information is plenty about how the frequency conversion itself works but it seems the issue of input and output. Proper termination is absolutely critical particularly the sum and difference or if. Somewhat prone to harmonic mixing.

Low level rf input voltage and a much larger lo pump signal. The pad provides proper termination to the si5351 and a proper drive to the diode mixers. With low level mixers a post mixer if amplifier is usually included to provide a broadband termination.

When using a high level mixer in a receiver the output intercept of the mixer is often equal to or higher than the input intercept of any low noise amplifier that can be designed to follow it. The simplest form of dbm termination is a 50 ohm resistor but this increases the overall loss and is therefore inefficient. Here a fully nonlinear analysis of a resistive diode mixer.