A Colpitts CMOS Quadrature VCO Using Direct Connection of Substrates for Coupling

Abstract

A new low-phase noise low-power quadrature voltage-controlled oscillator (QVCO) using differential Colpitts oscillator is presented. The proposed QVCO is composed of two identical current-switching differential Colpitts VCOs in which the first core VCO is coupled to the second in an in-phase manner, and the second core VCO is coupled to the first in an anti-phase manner. To couple the two core VCOs, the substrates of the cross-connected transistors as well as the substrates of MOS varactors are used; alleviating the need for any extra elements for coupling, which could add noise and increase power dissipation. A linear (sinusoidal) analysis is presented that confirms that the proposed circuit generates quadrature waveforms. The proposed coupling technique can be generalized to differential Colpitts VCOs for multiphase signals generation.Index Terms-Current-switching Colpitts-oscillator, low-phase noise, multiphase, quadrature oscillator.

Work in process: Integrated low phase noise Colpitts quadrature voltage controlled oscillator and mixer with charge-injection for Wimax communications and wireless networking application

“…The proposed VCO achieves the best phase noise of -121 dBc/Hz at 1 MHz offset frequency. Comparing with [3,5] and [6], 2 dB, 6 dB and 8 dB phase noise improvements respectively are obtained and 3 dB improvement with that of CMOS process [15][16][17]. The double-balance mixer measured by S parameter 4-port networking analyser the double-balance mixer result as show Table 2 and Table 3.…”

Analysis and review of main characteristics of Colpitts oscillators

“…Some of the Colpitts QVCOs 47–52 have been configured by coupling two VCOs through the body terminal of their transistors. These QVCOs should be designed based on the available triple well process.…”

Analysis and design of a new low‐phase noise and Gm‐enhanced class‐C quadrature VCO

“…In comparison with cross‐connected VCOs, while Colpitts cores have a better performance in terms of phase noise, they suffer from troublesome start‐up condition [4]. In order to alleviate this issue, several configurations are presented that relatively improve the start‐up condition and power dissipation [9–12].…”

“…Moreover, these structures [9–12] have reduced the flicker noise that degrades the close‐in phase noise of the circuit. However, most of these methods are based on Gm‐boosting and current switching techniques.…”