A low-power, high-frequency, all-NMOS all-current-mirror sinusoidal quadrature oscillator A. Leelasantitham, B. Srisuchinwong * School of Communications, Instrumentation and Control Systems, Sirindhorn International Institute of Technology, Bangkadi, Thammasat University, 160 Moo 5, Tiwanont Road, Bangkadi, Muang Pathumtani 12000, Thailand Received 5 March 2004; received in revised form 14 June 2004; accepted 17 June 2004 Available online 29 July 2004 Abstract A low-power, high-frequency, sinusoidal quadrature oscillator is presented through the use of only current mirrors where the small-signal paths are realized through all NMOS transistors. The technique is relatively simple based on (i) inherent time constant of current mirrors, i.e. the internal capacitances and the transconductance of a diode-connected NMOS, (ii) a negative resistance formed by a transconductance of a diode-connected NMOS load of a current mirror. No external passive components are required. As a particular example, a 2.83 GHz, 0.374 f T , 0.38 mW sinusoidal quadrature oscillator is demonstrated. Total harmonic distortions are less than 0.8%. The oscillation frequency is current-tunable over a range of 640 MHz or 22.62%. The amplitude matching and the quadrature phase matching are better than 0.04 dB and 0.178, respectively. A figure of merit called a normalized carrier-to-noise ratio is 158.23 dBc/Hz at the 2 MHz offset from 2.83 GHz. Comparisons to other approaches are also presented. q 2004 Elsevier Ltd. All rights reserved. Keywords: Sinusoidal quadrature oscillator; All-NMOS; Only current mirrors; Negative resistance; Low power; High frequency; Figure of merits 1. Introduction Quadrature oscillators (QOs) typically provide two sinusoids with 908 phase difference for a variety of applications such as in Hartley and Weaver image-reject receivers or in direct-conversion receivers [1]. Generally, QOs can be either non-linear or linear types. Non-linear QOs such as relaxation and ring QOs are usually realized using periodically switching mechanisms and therefore outputs may not be readily low-distortion sinusoids [2]. In contrast, linear QOs employ frequency-selective networks such as RC or LC circuits and consequently low-distortion sinusoids can be readily generated [3]. Existing RC techniques for QOs include all-pass filters [4] (or commonly known as phase shifters), operational transconductance amplifiers using capacitors (OTA-C) [5], operational transresistance amplifiers (OTRA) [6], negative resistance [3] and BJT current mirrors [7]. A related attempt to use only BJT current mirrors has been reported but only for a RC non-quadrature oscillator [8]. Such RC techniques, however, have suffered not only from relatively low oscillation frequencies between 1 and 8 MHz due to the use of relatively large off-chip capacitors, but also from relatively high power consumptions. Although alternative LC techniques using BJTs [9,10] or CMOS [11] offer high oscillation frequencies between 0.9 and 5 GHz, the ratios of the oscillation frequency (f 0 ) to the unity-gain frequency (f T ) [3] of a transistor are relatively small between 0.1 and 0.17 whilst their power consumptions are relatively high between 4.5 and 165 mW. Recently, non-linear QOs have exploited techniques using internal capacitances of either BJTs [12,13] or MOS [14] for high oscillation frequency between 1.4 and 11.5 GHz. However, the ratios of (f 0 /f T ) are in the region of 0.2–0.38 whilst the power consumptions are relatively high between 5.7 and 100 mW. On the other hand, existing linear (sinusoidal) quadrature oscillator has exploited the internal capacitances of only BJTs but suffers from 0026-2692/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2004.06.007 Microelectronics Journal 35 (2004) 713–721 www.elsevier.com/locate/mejo * Corresponding author. Tel.: C66-2-501-3505-20x1102; fax: C66-2- 501-3524. E-mail address: banlue@siit.tu.ac.th (B. Srisuchinwong).