RF chip ATE test transceiver from entry to abandonment

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3. Introduction to transceiver

First, a brief introduction to the transceiver , At present, the mainstream has superheterodyne structure Super heterodyne Architecture（ It requires two or more mixers to modulate the modulated RF signal to the intermediate frequency signal , Then apply I/Q Demodulator , Decompose the signal directly into I、Q baseband signal ）
Direct frequency conversion / Zero if architecture Direct Conversion (Zero-IF)【 RF signals do not need to be mixed , Directly through IQ Demodulator , Demodulate I、Q baseband signal 】
Direct RF sampling RF Sampling（ It's the one with higher frequency ADC, Direct will RF Radio frequency signal , Convert to digital signals , This method is suitable for occasions with low frequency and adoption rate , image 12bit ADC 10GS/s The price is still considerable , Accuracy is not high , Generally, the starting point of testing machine is 16-24bit）

This is a RFIC Basic principle block diagram of , The hardware involved is introduced in detail ：

（1） Antennas are divided into active and passive , Active antennas only have more amplifiers inside than passive antennas . Determining the shape and size of the antenna has 3 factors , frequency （ The lower the frequency , The larger the antenna size , It's usually 1/4 wavelength ）, Direction （ Omnidirectional antennas are usually larger than directional antennas ）, power （ Usually, the higher the radio wave transmission and reception power , The larger the antenna size ）. Of course, antenna is specially related to a discipline , It still involves a lot of content , If you're just doing tests , Feel that these are enough , If you are interested, you can also study the antenna gain （ Its essence is directional gain dBi）; Polarization （ Because radio frequency waves are transmitted in the air ,sine The wave itself has a direction , Vertical or horizontal , This direction is polarization . The combination of horizontal polarization signal and vertical polarization signal is circular polarization , Divided into right-hand circles RHC, Left hand round LRC）;

（2） The amplifier mainly involves 3 class , Low noise (LNA), It has a relatively low noise figure （NF）, Generally, the lower the noise, the more time it takes , Price cost . There is also high power （HPA）, Scale times LNA A little bigger , Part of the power is lost in the form of heat . Finally, a variable gain amplifier is introduced （VGA）, Most amplifier gains are fixed and VGA It can be adjusted by the control signal .
Usually the amplifier needs to measure linearity , Linearity is used to measure the degree to which the amplifier distorts the shape of the signal , among P1dB（1dB Compression point ） Is the highest linear power output of an amplifier . The other one is IP3(3 Order intermodulation point ) It's a fictional point. It doesn't exist in fact , It can be deduced by algorithm , generally speaking IP3 Than P1dB Big 10dB

（3） The filter is divided into low pass , qualcomm , Bandpass , Band stop , generally , The higher the frequency is. , The smaller the filter . filter (Filter） It is a passive component , No power required , Essentially, filters change their insertion loss （RL） Come to work , There is a special filter called SAW filter , Not satisfied with this conclusion ,SAW The working principle of the filter is to convert the RF signal into sound signal , Then turn the filtered sound signal into RF signal .

（4） Mixers , Evil mixer , Why? ？ Such a notorious nickname , It is because it introduces noise into the RF system , So usually there is a filter behind the mixer .mixer The purpose is to change the frequency of the signal but keep other characteristics unchanged , There are up conversion and down conversion , The signals are F+LO and F-LO. Generally speaking, the wider the frequency range , The greater the mixer loss , The worse the performance .