Advantages of Intermediate Frequency | disadvantages of Intermediate Frequency in RF System
This page covers advantages and disadvantages of Intermediate Frequency (IF) in RF system. It mentions benefits of advantages of Intermediate frequency and drawbacks or disadvantages of Intermediate frequency (IF).
What is Intermediate Frequency (IF) ?
The term IF refers to Intermediate frequency which lies between baseband frequency and carrier frequency on frequency spectrum. The technique of using IF is used both in RF Transmitter and RF receiver of various types for numerous reasons.
The figure depicts use of IF in RF Transmitter (i.e. up converter) and RF Receiver (i.e. Down converter). As shown IF frequency is fed to RF Mixer for up conversion using LO frequency. RF BPF (Band Pass Filter) is used to filter out undesired frequencies and to pass desired pass band frequencies. RF PA (Power Amplifier) is used to provide amplification to the signal before transmission into the air.
Like RF Transmitter, in RF receiver first signal is passed through LNA and then fed to RF mixer. RF mixer converts RF frequency to IF frequency. This IF frequency is filtered through IF BPF before it is converted into baseband I/Q signal. In RF receiver, received frequency spectrum which is at higher frequency is converted to spectrum centered at intermediate frequency which is at lower frequency.
There are three different types of RF receivers.
• Homodyne receiver
• Heterodyne receiver
• Superheterodyne receiver
In this RF receiver type called "homodyne", the modulated RF signal is directly converted to baseband I/Q at zero frequency or baseband frequency. Here RF mixers are not used. Refer Zero IF architecture >> for more information.
In this RF receiver type called "heterodyne", modulated RF signal is converted into modulated IF using single mixer conversion stage. This modulated IF signal is given to I/Q demodulator to derive information at baseband frequency.
In this RF receiver type called "superheterodyne", modulated RF signal is converted into modulated IF using double mixer conversion stage. First fRF is converted to fIF1 using RF Mixer#1 and than fIF1 is converted to fIF2. The modulated IF signal at fIF2 is given to I/Q demodulator to derive information at baseband frequency.
Benefits or advantages of Intermediate Frequency (IF)
Following are the benefits or advantages of Intermediate Frequency (IF):
➨The RF components are less expensive at such lower intermediate frequencies than higher radio frequencies.
➨As the IF based approach converts multiple RF carriers into signal IF, it makes receiver design simpler. This reduces number of RF components required for RF receiver design.
➨Filtering of IF signal is easier than RF signal as it requires lower Q-factor due to reduction in carrier frequency.
➨The receivers using IF approach offer better sensitivity than zero IF receiver architecture.
➨The superheterodyne receiver architecture prevents image noise foldover due to use of two IF frequencies before conversion to baseband frequency.
➨As we know mismatch between amplitude/phase of IQ signal lead to errors in demodulated data information. This is more prominent in non-IF architecture due to I/Q separation at higher frequencies in IQ demodulator.
Drawbacks or disadvantages of Intermediate Frequency (IF)
Following are the drawbacks or disadvantages of Intermediate Frequency (IF):
➨It makes RF transmitter and RF receiver expensive. This is due to requirement of RF Mixers, LOs and Band Pass Filters (BPFs) at various stages. It requires Local Oscillators to feed at one of the input of RF Mixers used for conversion.
➨Often RF Transceivers designed using IF approach need filters to stop LO leakage and to prevent image frequencies in specific designs. This further increases cost of IF based Transmitters and receivers.
Refer advantages and disadvantages of Homodyne architecture >>.