High-frequency two-input CMOS OTA for continuous-time filter applications

Abstract

A high-frequency fully differential CMOS operational transconductance amplifier (OTA) is presented for continuous-time filter applications in the megahertz range. The proposed design technique combines a linear cross-coupled quad input stage with an enhanced folded-cascode circuit to increase the output resistance of the amplifier. SPICE simulations show that DC-gain enhancement can be obtained without significant bandwidth limitation. The two-input OTA developed is used in hgh-frequency tuneable filter design based on IFLF and LC ladder simulation structures. Simulated results of parameters and characteristics of the OTA and filters in a standard 1 . 2~ CMOS process (MOSIS) are presented. A tuning circuit is also discussed.

Bulk linearized CMOS differential pair transconductor for continuous-time OTA-C filter design

“…There are many papers describing gate driven [7][8][9][10][11][12][13] and bulk driven MOS pairs [14][15][16][17][18][19][20][21]. A simple gate driven MOS pair unfortunately has poor linearity of voltage to current conversion, therefore the other voltage to current converters are often used when the linearity is important [7].…”

“…The transconductance-capacitor (OTA-C) approach is often used for continuous-time filter design [1][2][3][4][5][6]. For high frequency applications, numerous circuit techniques to design OTA-C filters have been developed, using the gate-driven differential pair transconductors as input stages of the OTAs [7][8][9][10][11][12][13]. On the contrary, the transconductors with bulk-driven differential pair have been proposed for low frequency OTA-C filter applications [14][15][16][17][18][19][20][21].…”

Performance comparison of high-order IFLF and LF linear phase lowpass OTA-C filters with and without gain boost

“…For fully differential voltage-mode MLF filters [4], multiple input OTAs are needed [35], while multiple output OTAs [36] are required in fully differential currentmode filters [7]. The seventh-order lowpass LF and IFLF OTA-C filters designed in the above are simulated for the cut-off frequency of 125 MHz using the proposed multiple input OTA given in Fig.…”

“…A number of OTAs have been proposed in the literature [32][33][34][35][36]. For fully differential voltage-mode MLF filters [4], multiple input OTAs are needed [35], while multiple output OTAs [36] are required in fully differential currentmode filters [7].…”

Second-order OTA-C filters using a single OTA

“…1 requires a multiple-input OTA with two output currents both flowing out of the OTA. To benefit from its advantages of linearity and tunability [5,6] we use the cross-coupled type OTA in the filter simulation, shown in Fig. 3.…”