A Very Linear Low-Pass Filter with Automatic Frequency Tuning

Abstract

A Gm-C third-order Chebyshev low-pass filter with a novel switched capacitor frequency tuning technique for a zero-IF Bluetooth receiver has been designed. The frequency tuning scheme is simpler and has more relaxed specifications than conventional ones. Furthermore, a highly linear pseudo-differential transconductor with a compact feedback loop able to operate with low supply voltage has been used. This control loop holds the input transistors in triode region and provides high output resistance, keeping high linearity in a wide range of transconductance. The filter bandwidth is 0.5 MHz and the overall scheme consumes 1.1 mA from a 1.8-V supply. The measured third-order intermodulation (IM3) distortion of the filter for a 1 Vpp two-tone signal centered at 300 kHz is 65 dB.

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

“…4) are used in the adaptive biasing circuit to adjust the value of r ds Ma8 in (8) and V Ref in (6), respectively. By this way, the adaptive biasing circuit can be adjusted to result highest linearization for each tuning condition of OTA.…”

“…Hence, direct conversion receivers with most integration capability and design of tunable circuits as building blocks have been interested in recent research [5][6][7][8][9].…”

CMOS Analog Filter Design for Very High Frequency Applications

“…On the other hand, some drawbacks related to the use of CMOS gm-C filters also poke out: their parasitic capacitances are often considerable and require to be taken into account in advance in the design procedure [13]; at high frequencies, the value of the transconductance varies with frequency [15]; their useful signal dynamic range is rather low due to the nonlinearity inherent to the MOS transistors [14]. Despite those disadvantages, huge efforts have been made in order to achieve gm-C structures with a salient functionality at very high frequencies [16,17], and with improved linearity [18,19].…”

Adaptive cancellation linearisation and its application to wide‐tunable Gm‐C filter design

“…Highest level of integration is achievable by hardware sharing through employing reconfigurable building blocks [1,2]. Hence, recently most research on the design of receivers is focused on the multi-standard direct conversion type which can support two or more applications and therefore has advantages of lower cost and lower area usage [3][4][5][6]. Channel select filter as an important part of the direct conversion receivers is responsible for selecting desired channel, blocking interferers and providing anti-alias filtering before the subsequent analog-to-digital conversion stage [7,8].…”

“…However, the open loop operation of operational transconductance amplifiers (OTA) leads to more non‐linearity of Gm‐C filters [11–14]. The solution that has been presented in many literatures [1–29] is to design highly linear OTA.…”