DESIGN STABILITY CONTROLLER CIRCUIT OF CHANNEL SELECT FILTER IN WIMAX DIRECT CONVERSION RECEIVER WITH VARIABLE BANDWITH

• Main Author: WIDYO ISWORO (NIM 13203142), LAKSONO
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/10788
• Institution: Institut Teknologi Bandung

<p align="justify">During the last decades more and more wireless standards have been introduced. These various kinds of wireless standards provide us more alternatives communication ways. A standard usually has a certain specification for its device, thus it makes us adjust in providing communication devices. This situation encourages innovation in design a multistandard receiver. To achieve this, a receiver RF front end needs to have re-configurable building blocks.<p align="justify"><p>With using direct-conversion receiver, a multistandard communication receiver can be realized. This architecture has lower power consumption, cheaper, and higher integrity aspect than superheterodyne that is used in communication devices mostly. Direct conversion's RF front end part that needs to be configured is baseband channel select filter.<p align="justify"><p>In this final project, the writer together with Faisal Rachmadianto design a baseband channel select filter direct conversion receiver for WiMAX standard with 1.75 MHz, 3.5 MHz, 7 MHz, and 10 MHz bandwidth. The writer designs the stability controller circuit for baseband filter, whereas the baseband filter circuit is designed by Faisal.<p align="justify"><p>From the calculation result, that derived from WiMAX receiver spesification, known that the system needs 7th order baseband filter. The distribution of the filter order is the first pole is already part of the mixer output stage and the remaining is implemented in baseband filter. The 6th order filter is split into three 2th order filters which are arranged cascaded. The writer uses 2th Butterworth filter to design the baseband filter. For its implementation, GmC topology is chosen due to its easily configurable feature by adjust its transconductance. Realizing GmC topology to be the active filter is achieved by gyrator method. This method is used to synthesize active filter from passive filter prototype.<p align="justify"><p>The baseband channel select filter circuit consist of two main parts, they are the baseband filter circuit and the stability controller circuit. The baseband filter circuit uses the fully differential folded-cascoded OTA topology. This topology has noise robustness and high impedance output. Whereas the stability controller circuit consist of the biasing circuit and the common-mode feedback (CMFB) circuit. CMFB circuit controls the common-mode signal that can't be stabilized using negative feedback and suppress the common-mode signal that can affect the output signal level and saturate the other component. The biasing circuit supplies bias current for all of the transistors in order to be in active region.<p align="justify"><p>The stability parameters that watched are step response, common-mode rejection ratio (CMRR) and power supply rejection ratio (PSRR). From the simulation result known that the designed baseband filter circuit has slew rate 1.81 V/us and settling time 0.3 us. It also has good resistance of common-mode signal and ripple voltage of power supply, this shown by the high CMRR and PSRR about 60-130 dB and 50-85 dB respectively. So it can be concluded that the designed baseband filter has good stability aspect.