Gm-C Filter Design Research Articles

A new controllable adaptive biasing linearization technique for a CMOS OTA and its application to tunable Gm-C filter design

This paper presents a new linearized operational transconductance amplifier which uses a fully controlled adaptive biasing scheme. The differential input voltage is sensed through a squarer circuit and is compared with a controllable reference voltage to create appropriate auxiliary tail currents. The proposed adaptive biasing circuit can be adjusted to make best linearization for each tuning condition of OTA. While the adaptive biasing circuit consumes a little portion (about 13%) of the total power consumption (about 475μW), it significantly reduces the third-order nonlinearity of OTA׳s output current in whole of its tuning ranges. By applying a two-tone 0.6Vp-p input voltage at 20MHz, IM3 is degraded by more than 13dB throughout the transconductance tuning range from 8.2μA/V to 47μA/V. Proposed OTA is employed to implement a wide tunable Gm-C filter. The cutoff frequency of low-pass filter is tunable from 584kHz to 10.6MHz, thus, it covers several standards of wireless applications. IIP3 of filter is 22.3dBm, 19dBm and 17.4dBm, respectively, for Bluetooth, UMTS and IEEE 802.11a/g standards. The OTA and Gm-C filter are designed and simulated in 0.18-μm TSMC CMOS technology with Hspice simulator. Monte Carlo and corner case simulations show the good robustness of proposed circuits against the fabrication errors.

A linear compact tunable transconductor for Gm-C applications

A CMOS highly linear voltage-controlled transconductor suitable for Gm-C filter design is presented. The control loop to program the transconductance maintains the input transistors in triode region with a compact topology. Measurement results for the transconductor fabricated in a 0.5-μm CMOS technology feature a spurious-free dynamic range (SFDR) of 72 dB for 1 Vpp differential inputs at 1 MHz. The voltage to current converter ensures a high linearity level for a wide transconductance range. Functionality of the transconductor is shown in a fifth-order Gm-C tunable complex filter well suited for a dual-mode Bluetooth/Zigbee transceiver.

CMOS linear programmable transconductor suitable for adjustable Gm-C filters

A novel CMOS linear programmable transconductor is presented. It is based on a telescopic cascode operational transconductance amplifier with source degeneration implemented by means of highly linear tunable active resistors. The transconductor has been designed in a 0.5 µm CMOS technology featuring a third-order intermodulation (IM3) of −54.8 dB at 10 MHz for a 1 Vpp output voltage. Its feasibility for Gm-C filter design has been experimentally validated with a 1 MHz tunable third-order Chebyshev lowpass filter suitable for Bluetooth applications.