Biography
Enrollment Date: 2014
Graduation Date：2017
Degree：M.S.
Defense Date：2017.05.24
Advisors：Ziqiang Wang
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Research on Key Technology of High Linearity IF Analog Baseband for Superheterodyne Receivers
Abstract:
Nowadays, wireless communication technology plays an increasingly important role in our world. In the future, wireless communication technology will continue to play a key role in the application of artificial intelligence, smart home, Internet of things and intelligent transportation, aerospace and other applications. These application backgrounds require wireless communications to develop toward a highly integrated, low power consumption, portable direction. Therefore, it is vital for realizing the on-chip integration and high performance of the wireless communication chip.
The analog baseband chip of this paper was used in superheterodyne receiver. Although superheterodyne receivers commonly used in the external mirror suppression filter and analog IF filter so that affecting the stability of the system, the communication quality of the transceivers with the superheterodyne structure is very good, so it is widely used. The analog baseband circuit of the superheterodyne receiver consists of an analog IF filter and a programmable gain amplifier (PGA). Analog IF filter is generally a low-pass filter or band-pass filter, mainly plays a role in suppressing the out-of-band signal. PGA is based on the strength of the received signal to sure the different magnification so that the output signal in a certain power range. The analog IF filter in the superheterodyne receiver needs to be switched in a very narrow frequency band and has a high rejection capability for adjacent channels, which makes it necessary to have a high Q value and order N. As a result, on-chip integration of analog IF filters becomes difficult.
This thesis designed a bandpass filter with a center frequency of 70MHz and a bandwidth of 22 MHz. The linearity of the bandpass filter is greater than 25dBm, and such high bandwidth and linearity require the bandwidth gain product (GBW) of the Op-amp reach to at least 250GHz, so the Op-amp cannot be achieved at all. In this thesis, through the integrated frequency compensation (IFC) technology to effectively reduce the requirements of Op-amp, and making the analog IF filter can be integrated on-chip. In addition, for the cascade system such as filters, the noise and linearity of the system are mutually constrained. Therefore, the thesis introduces the optimization techniques of the filter`s linearity and noise. Through the optimization, the output 1dB compression point of the filter from 5dBm to 10.5dBm, the noise figure also has a certain improvement, but increased the area of the layout. For the analog baseband circuit of high bandwidth and high linearity, the design of high-performance Op-amp is the core. In this thesis, through the feedforward compensation technology and anti-pole splitting technology to effectively reduce the power consumption of op-amps, and ultimately achieved a high-performance op-amp of GBW greater than 10GHz. In the process of Tsmc90nm, the layout area of bandpass filter with a center frequency of 70MHz reached to 413um*1058um. In addition, this thesis also designed a low-pass filter with 30MHz, 50MHz, 180MHz bandwidth adjustable and a PGA with a dynamic range from 0dB to 25dB in the process of Tsmc65nm. Since the resistors and capacitors of the filter are deviated from the process when they are manufactured, this thesis introduces the automatic calibration technique, which automatically calibrates the center frequency and bandwidth of the filter.
The thesis presents a measurement results of a bandpass filter which with a center frequency of 70 MHz and a bandwidth of 22 MHz cascaded a PGA which with AGC loop. The measurement results showed that the center frequency was 70MHz, the bandwidth was 22.73MHz, the out-of-band suppression reached to 46.7dB, the output 1dB compression point achieved 3.4dBm, the band without ripple and tilt condition.