A 3^rd order OTA-C low pass filter for W-CDMA standard applications in zero-IF receiver

Abstract

This work presents the design of a 3 rd -order low-pass OTA-C filter for W-CDMA protocol wireless communications applications. The filter is designed for Butterworth response with corner frequency of 2.68 MHz, stop-band frequency of 10 MHz, pass-band ripple of 3 dB and stop-band attenuation of 34 dB. Filter design is performed in OnSemi 0.5µm CMOS process. The involved transconductor consists of a single-stage fully-differential OTA with dynamic source degeneration and common mode feedback. 978-1-4673-6155-2/13/$31.00

A Configurable Interface for Analog Sensor Outputs

“…In order to achieve linear transconductance or Gm characteristics, linearization techniques such as current division [11] and source degeneration [12] are required. Transconductance of the OTA is the same as the transconductance of the differential PMOS transistors gm1,2, which is equal to √ 2.…”

“…Therefore, source degeneration method has also been applied to the OTAs because current division method alone is not sufficient to remove the third harmonic term. Unlike in the conventional approach, source degeneration method uses resistors; however, they are replaced by transistors operating in triode region because resistors add parasitics, cause thermal noise, occupy large area, and decrease individual and overall transconductance of OTAs [12]. As shown in Figure 11, when degeneration transistors M3, M4, M33, and M44 are matched well, it is possible to obtain higher transconductance.…”