RF content learning

Superheterodyne receiver notes ：5. Communication electronic circuit RF transceiver structure (1)_ Bili, Bili _bilibili

1 Superheterodyne - Image interference problem

Can't block wIM There is also a certain frequency , This causes the same phenomenon after mixing wIF interfere

Useful signals 1 And jamming signals 2, If to if wLO The interval difference is the same , There will be mirror interference .

2 Image interference solution

2.1 Front end filter

To filter Q High value requirements , Band stop filters are commonly used in engineering

2.2 Increase if

In short ： Stay away

  But the frequency increases , The difficulty of design will increase . Therefore, if frequency should be designed reasonably .

After high frequency , Yes

2.3 Zero IF receiver

  High and medium frequency , Therefore, zero if is also feasible .

2.3.1 Advantages of zero if

 2.3.2 The disadvantage of zero intermediate frequency

  Zero if - LO leakage problem

  Zero if - DC offset problem

Capacitive coupling technology Eliminate DC offset ：

Large coupling capacitance is required , Difficult to integrate
Establishment time is too long , example 200Hz The turning frequency requires 2ms Set up time
Only applicable to Dc Communication system without modulation information nearby

DSP Compensation technology Eliminate DC offset ：

Use the... In the digital baseband DSP, Calculate DC offset , And feed back to the front end for offset
The difficulty is that the self mixing signal is generally a time-varying signal , Difficult to eliminate dynamically

  Zero if - Even intermodulation distortion

 

 

  Zero if -IQ Mismatch problem

 

Zero if - Flicker noise problem

 

2.4 Low IF receiver

Focus on one problem ： Image suppression problem

 

6. Communication electronic circuit RF transceiver architecture (2)_ Bili, Bili _bilibili

The following introduces Hartley structure 、90 Degree phase shift network 、Weaver Structure anti mirror frequency domain characteristics 、 Index and calculation of the system

1：12：11 Begin to introduce Low noise amplifier