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Semi Conductor Readiness

 

Up until 5G implementation, we didn't have to worry too much of this level of readiness : Semi Conductor/Transistor level readiness since the technology in semi conductor was mostly going ahead of Wireless communication technology requirement and the semicoductor technology to meet 5G requirement was available before 5G requirement was finalized. But the situation seems to be different in 6G. The semiconductor technology available now seems to be far from being ready to meet 6G requirement. Therefore, we would need to keep close eye on the technical evolution in this aready as we form the detailed 6G requirement and check the feasibility of achieving those requirement.

 

Following is the summary of status on the semiconductor technologies that would be critical to implement the electrical components for 6G.

 

Source : Hera-X : Deliverable D2.1 Towards Tbps Communications in 6G: Use Cases and Gap Analysis

 

Source : ETSI GR mWT 022 V1.1.1 (2021-04)

 

Highligts to note : Followings are some of the highlights that you would notice from the data shown above.

  • Most of the technologies can cover the 10~100 Ghz range.
  • Below 10 Ghz : CMOS would be dominant for low/mid power and GaAs would be dominant for high power.
  • Over 100 Ghz : SeGe would be better option.
  • Over 200 Ghz : InP would be dominent option.
  • In general, as frequency goes higher. The saturation Tx power tend to decrease.

 

 

Some important parameters to be noted for the performance / characteristics of this technology are as follows :

  • f_T : the frequency at which Transistor Current Gain drop to 1 (0 dB)
  • f_max : the frequency at which Transistor Power Gain drop to 1 (0 dB)
  • Power Generation Capability : Important for PA
  • Noise Figure : Important for LNA
  • Linearity
  • Signal Combining
  • Power Consumption
  • Spectral Efficiency
  • Form Factor

NOTE : As a rule of thumb, the transistor f_T/f_max should be more than twice the operating frequency (i.e. the RF carrier frequency) to obtain decent gain and efficiency in amplifier design (quoted from WHITE PAPER ON RF ENABLING 6G – OPPORTUNITIES AND CHALLENGES FROM TECHNOLOGY TO SPECTRUM)

 

WHITE PAPER ON RF ENABLING 6G – OPPORTUNITIES AND CHALLENGES FROM TECHNOLOGY TO SPECTRUM states as follows :

    Although there are already technologies that can achieve operation in the range of 100–1,000 GHz, the implementation of any larger system like an RF transceiver will be much more difficult than for 5G frequencies in the lower mmW region. One must remember that even at lower mmW frequencies, it is impossible to achieve similar performance to frequencies below 6 GHz with the same power consumption. The limitations arise from physics and the boundaries of different semiconductor technologies.

 

 

 

Considerations on the overal Radio Front End

 

As the technologies for individual transistor evolves to meet the 6G requirement, we have to re-evaluate those technologies in terms of the structure of the whole front end. The overall sturcture of transmiter and reciver front end can be illustrated as below and we need to check if the technology for each segment of the frontend is ready and also need to consider how to integrate each of the segment to build the whole frontend module.

 

 

A,H - ADC/DAC : The critical question at this stage would be 'Is there ADC/DAC which can provide such a huge sampling rate and enough bit resolultion to meet the 6G Bandwidth requirement ?'.  Usually as sampling rate and bit resolution goes higher in ADC/DAC, power consumption increase. Then another question is 'how to improve power efficiency ?'

 

B,G - PLL : Would there be any PLL technology that can operate in 6G spectrum in fundamental frequency mode ? If it cannot operate in fundamental mode in 6G spectrum, we need to multiply the frequency or use harmonic frequency, but the performance would degrade in such cases.

 

C - Power Amplifier : The critical questions at this stage would be 'Is there Power Amplifier working at such a high frequency with enough power ?'. Usually the operating frequency goes very high like 6G spectrum, the maximum power that a power transistor can output tend to be limited.

 

C - Low Noise Amplifier : Would there be any LNA operating in 6G spectrum with low enough Noise Figure ?

 

 

 

AD Converter

 

Regarding AD Converters, generally several questions as follows are the important ones to be answered.

  • What is the maximum sampling rate ?
  • What is the bit resolution ? (i.e, How many bits are required for each sample ?)
  • What is the power consumption ?

In general, maximum sampling rate would be limited by the available semiconductor technology, the bit resolution would vary depending on processing performance and the power consumption would be affected by sampling rate and bit resolution.

A common way to estimate a ADC taking all three factors is to use FOM (Figure of Merits) as described below.

 

 

 

 

Noise Factors on Rx Chain

 

As described above, the major issue on Tx chain is how to develop Power Amplifiers that can pump up enough power. What is the major issue (critical factor) on Rx chain. It is how to decrease the noise factor of the whole reciever chain. The estimation of noise factor on reciever chain can be summarized as below based on Hera-X : Deliverable D2.1 Towards Tbps Communications in 6G: Use Cases and Gap Analysis