PIN/Schottky Diode in RF Mixing: Working & Benefits

Introduction : RF mixing is the process of combining two radio signals to produce sum and difference frequencies, essential in receivers and transmitters. PIN and Schottky diodes are often utilized due to their speed, low capacitance and good switching characteristics. This page explains how RF mixing works with these diodes and the key performance benefits they bring.

Diode based RF Mixing Circuit Working

The figure depicts simple circuit which can be used as RF mixer. It consists of two LO inputs provided as input to single diode (1N4148) after they are passed through respective capacitors and resistors.

RF mixing multiplies two signals creating sum and difference frequencies. If there are two input frequencies i.e. f1 and f2, output contains various components of these input frequencies. Output can be f1 +/- f2 , 2f1 +/- f2, f1 +/- 2f2, 3f1 +/- f2 etc. Desired products are filtered out from these output combinations.

• For up conversion : f_RF = f_LO + f_IF
• For down conversion : f_IF = f_RF - f_LO

Advantages of diode in RF Mixers

Following are some of the benefits of diode based rf mixers.

1. Due to use of passive mixers in its design, it does not require external DC power. Hence it reduces power consumption and simplifies design.
2. Balanced diode mixers offer good linearity by suppressing even order harmonics and reducing intermodulation distortion.
3. Diode mixers operate over wide bandwidth.
4. Passive diode mixers are more tolerant to handle high RF input signal levels compared to some active mixers counterpart.
5. Double balanced or ring diode mixer configurations offer good port isolation between LO, RF and IF.
6. Diode mixers are simpler to implement and cheaper to produce.
7. Passive diode mixers are passive which do not introduce noise from internal biasing.

Conclusion: Using PIN or Schottky diodes in RF mixing delivers high speed, low loss and reliable frequency conversion with minimal distortion.