Advantages of RF Mixer | Disadvantages of RF Mixer

This page covers advantages and disadvantages of RF Mixer device. It mentions benefits or advantages of RF Mixer and drawbacks or disadvantages of RF Mixer.

What is RF Mixer ?

Introduction:
It is a three port RF signal mixing device which converts one frequency signal value to the another frequency value. It is used to convert high frequency value to low frequency value and vice versa. In transmitter, it converts low frequency signal to high frequency signal. In receiver, it converts high frequency signal to low frequency signal. RF Mixers are used in radio frequency (RF) transceivers, RF transmitters and RF receivers for frequency conversion.

RF Mixer

Fout of RF Mixer = finput1 +/- finput2

Figure-1 depicts circuit symbol of RF mixer. The three ports are commonly designated as LO, IF and RF. Return losses at the three ports are called S11, S22 and S33. Insertion losses between ports are called S21 (from port1 to port2), S23 (from port3 to port2) and S13 (from port3 to port1).

RF Mixer Output components

The figure-2 depicts RF mixer spectral components at the output. In addition to sum and difference of the input frequencies, it generates harmonics and spurious frequencies at its output as shown. RF filter is used at the output of the RF mixer to filter out desired frequency components.

Up Down conversion using RF mixer

Following are the selection parameters of RF Mixer.
• Frequency range : Datasheets of RF mixer specify IF, RF and LO frequency range. So one has to check the same for selecting appropriate mixer for design.
• Dynamic range: Input power range over which mixer is useful.
• LO power level : This parameter specify power level of LO signal required to obtain best performance of RF mixer.
• Conversion loss (in dB): This parameter specify amount of power lost during frequency conversion by RF mixer.
• 1-dB input compression level : It specifies RF power at which the conversion loss increases by 1 dB.
• TOI (Third Order Intercept Point) : This parameter measures nonlinearity of the device. This should be high to prevent generation of undesired harmonic frequencies and IMD products.
• Isolation: This parameter specifies Isolation between the various ports viz. RF, LO and IF. It should be higher to prevent interference from other RF signals.
• Other parameters : VSWR (or return loss), Noise figure, size, cost, form factor, temperature dependancy, package type etc.

Benefits or advantages of RF Mixer

Following are the benefits or advantages of RF Mixer:
➨It is used for frequency conversion and hence same antenna can be used to transmit and receive multiple frequencies.
➨It increases SNR (Signal to Noise Ratio) of weak signal by mixing it with high power LO signal and translating it to other frequency.
➨It also increases sensitivity of the receiver by mixing weak signal with high power LO signal.
➨They are designed using cheaper components and hence they are available at inexpensive rates.
➨RF mixers are available in various package types such as SMT (Surface Mount Technology), Plug-in with through hole mounting with pins, connectorized etc. Due to this, they are easy to be used in RF circuit designs, PCB mounting and testing purpose respectively.

Drawbacks or disadvantages of RF Mixer

Following are the limitations or drawbacks or disadvantages of RF Mixer:
➨RF mixers introduce signal loss during frequency conversion process. Hence check conversion loss of the RF mixer during RF circuit design.
➨RF mixers support limited frequency range. Hence choose RF mixers as per desired frequency range at its three ports.
➨RF mixers are nonlinear RF components. Hence they produce unwanted harmonic frequencies and IMD (Intermodulation) products. Hence choose RF mixers with higher isolation between its ports. RF filters are often required to suppress undesired frequencies at its output in RF circuit designs. Use of filters increase overall cost of the RF system under development.
➨RF Mixers increase NF (Noise Figure) of the circuit and degrade SNR (Signal to Noise Ratio). This lowers performance of the RF circuit. Hence proper amplifier devices are also used in the RF chain to meet RF signal gain requirement of the RF circuit.



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