[Circuit] RF Mixers

Where is an RF mixer? 

1) a general description of RF mixers 

2) consisted of three passive ports or active devices that can modulate a signal. 
  a. RF input port (R)
  b. Intermediate frequency output port (I) 
  c. Local input port (LO)
3) The purpose of RF mixers
  a. changing the frequency of an electromagnetic signal with conserving other quantities (amplitude and phase) from the initial signal 
   - i.e. Heterodyning (a process in which output frequency is shifted from one frequency range to another) 
  b. 

Where is an RF mixer used? 

1) RF/microwave applications 
2) military radar 
3) cellular base stations

Three different ports of RF mixer? 

1. Local input port (LO) 
  - depending on the purpose, the LO is typically driven by square or sinusoidal waves 
  - In concept, the LO play a role as a gate of the mixer in which the mixer is considered on(off) when the LO has a large(small) voltage
  - the LO cannot be used as an output port.
    (Note that RF and Intermediate ports can be used as input or output ports)

Downconversion and upconversion of RF mixers 

 

 

Active RF mixer and Passive RF mixer 

Note that active and passive RF mixers have their own advantages and disadvantages. Thus, depending on the purpose, these two mixers are used respectively. 

1) Active RF mixer 
   - made up of active devices such as transistors and vacuum tubes (i.e. amplifying devices) to increase the strength of the product signal
   - improvement of isolation between ports 
   - higher noise and more power consumption
   - less tolerant of overload  
   - mostly used for RFIC implementation 
2) Passive RF mixer 
   - made up of passive devices such as diode
   - due to diode, it relies on nonlinear characteristics between voltage and current
   - widely used due to its simplicity, wide bandwidth, and good intermodulation distortion (IMD) performance
   - In a passive RF mixer, the desired power of the output signal is always lower than the input signals 

Three different types of RF mixers 

 

Important parameters associated with mixers 

 

 

 

Example: ZAD-3 mixer
1) Manual: https://www.minicircuits.com/pdfs/ZAD-3+.pdf   

 

Reference 
[1] https://www.digikey.com/en/articles/the-basics-of-mixers   
[2] https://www.markimicrowave.com/assets/appnotes/mixer_basics_primer.pdf