A linear fully balanced CMOS OTA for VHF filtering applications

Abstract

A linear, fully balanced, voltage-tunable CMOS operational transconductance amplifier (OTA) with large dc gain and wide bandwidth is described. The approach uses a twodifferential-pair transconductor with a cross-coupled input stage together with a negative resistance load for compensating the parasitic output resistance of the OTA. Since no additional internal nodes are generated, dc gain enhancement is obtained without bandwidth limitation. SPICE simulations show that total harmonic distortion at 1.42 V p -p is less than 1% with dynamic range equal to 66 dB at a power consumption of 2.7 mW from a single 5-V supply. As an example, the OTA is used to design a third-order elliptic lowpass filter in the very-high-frequency range, simulated in a standard 2 m CMOS process (MOSIS).The cutoff frequency of the filter is tunable in the range of 12-50 MHz.

A field programmable analog array for CMOS continuous-time OTA-C filter applications

“…There is tradeoff between noise performance and large-signal handling capability at the input of the cross-coupled OTA. Some simulation results confirming this were given in [16].…”

“…The simplified schematic diagram of the OTA based on two cross-coupled differential MOS pairs [16] and digitally programmable current mirrors is shown in Fig. 2.…”

“…2, thermal channel noise is assumed to be the dominant noise source. Thus, the equivalent input-referred voltage noise can be approximated by [16], [20], [21] as (7) where is Boltzman's constant, is the absolute temperature, --, , , and with . From (7), it is seen that optimum noise performance of the OTA stage is achieved by minimizing .…”

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

“…One of the standard techniques to improve the CMRR, PSRR and dynamic range of analogue integrated filters is to use fully differential structures [6, 71. Many OTAs suitable for such applications have been reported in recent years [2][3][4][5][8][9][10].…”

“…An analysis of the influence of second-order effects on a smilar transconductance stage has been reported in [9]. The input stage remains linear if the following scaling condition is fulfilled:…”