Superheterodyne Receiver: Advantages and Disadvantages

This page explores the advantages and disadvantages of the superheterodyne receiver architecture. We’ll compare it to the heterodyne receiver and discuss the pros and cons of each.

What is a Superheterodyne Receiver?

Introduction:

• A Heterodyne receiver uses a single RF mixer to convert a modulated RF signal to baseband I/Q signals.
• A Superheterodyne receiver employs dual RF mixers for the same conversion process.

Both heterodyne and superheterodyne receivers use a Local Oscillator (LO) frequency that is different from the received signal frequency.

Figure 1: Heterodyne receiver architecture

In the heterodyne receiver (Figure 1), the Intermediate Frequency (IF) is calculated as:

fIF = fRF - fLO

To understand more about up and down conversion, refer to RF Mixer basics and the RF Mixer tutorial.

Figure 2: Superheterodyne receiver architecture

The superheterodyne receiver (Figure 2) uses a two-stage down conversion process. The equations are:

fIF1 = fRF - fLO1 (Equation 1, Stage I) fIF2 = fIF1 - fLO2 (Equation 2, Stage II)

The modulated fIF2 is then processed to get baseband I/Q signals at zero frequency.

You may want to refer to Homodyne Vs Heterodyne Receiver for additional information.

Benefits of Superheterodyne Receivers

The following are the benefits (advantages) of superheterodyne and heterodyne receiver architectures:

• Lower Frequency Processing: Converting the high RF frequency to a lower IF allows all subsequent processing to occur at these lower frequencies. Components are generally cheaper at lower frequencies compared to higher ones.
• Easier Filtering: It’s easier to filter the IF signal compared to filtering the original RF signal.
• Better Sensitivity: Superheterodyne receivers offer better sensitivity compared to homodyne receiver architectures.
• Image Noise Reduction: The superheterodyne receiver architecture, with its dual conversion, helps prevent image noise foldover due to the use of two IF frequencies before conversion to baseband. The heterodyne receiver architecture uses single conversion.

Drawbacks of Superheterodyne Receivers

The following are the disadvantages of superheterodyne and heterodyne receiver architectures:

• Increased Complexity and Cost: Superheterodyne receivers require additional Local Oscillators (LOs) and RF mixers to convert the signal from RF to IF before converting to baseband. This increases the overall receiver cost.
• Need for Additional Filtering: Filters are also needed to remove any LO leakage and undesired frequency components to prevent image frequencies. This further adds to the cost and complexity of the receiver.