Switched-capacitor Oscillator Research Articles

An area‐efficient switched‐capacitor relaxation oscillator with digitally controlled frequency tunability

AbstractThis paper describes a programmable low‐jitter switched‐capacitor (SC) square‐wave oscillator for the use in a variety of voice‐band signal‐processing applications. The core of the circuit is a relaxation oscillator whose oscillation frequency programmability does not resort to variations either in capacitor values or in the sampling frequency. As a result, total capacitance is reduced and, hence, silicon area is minimized while low phase jitter and high resolution programmability are achieved. Simulation results referred to the design of an SC oscillator in 0.35‐µm CMOS technology are presented to demonstrate the feasibility of the proposed approach. Copyright © 2008 John Wiley & Sons, Ltd.

Nonlinear Shaping SC Oscillator With Enhanced Linearity

A nonlinear shaping technique for a switched-capacitor (SC) bandpass filter (BPF) based oscillator yielding enhanced linearity is presented. Usually, for an SC oscillator consisting of a BPF and a two-level comparator, the linearity can only be improved by increasing the quality factor (-factor) of the BPF. This paper proposes an efficient way to improve the linearity of SC BPF-based oscillators. In particular, by replacing the conventional two-level comparator by a sound multilevel comparator, a nonlinear shaping of the signal at the output of the comparator causes a significant improvement in linearity. To illustrate the effectiveness of the proposed technique, one conventional SC BPF-based oscillator and the proposed oscillator have been designed and fabricated in a standard 0.35- CMOS technology. Each oscillator was designed to operate from a 1.65 V supply voltage and a master clock frequency of 80 MHz. The oscillation frequency is 10 MHz and the -factor of the BPF is 10. Experimental results demonstrate that the proposed scheme improves the third-order harmonic distortion by 20 dB with respect to the conventional SC BPF-based oscillator.

Excess phase jitter cancellation method for SC relaxation oscillators

A practical jitter cancellation method for relaxation SC oscillators is presented. Two versatile switched-capacitor (SC) oscillators using the proposed excess phase jitter suppression technique are described. The jitter and the dependence of the oscillation frequency on the saturation voltages of operational amplifiers (op-amp) or comparators are eliminated. Therefore, there is no oscillation frequency limitation, except the one determined by the Nyquist rate. Because the frequency of oscillation of the proposed SC oscillators depends on a capacitor ratio and a reference voltage, the oscillators have excellent stability and accuracy. Experimental results showed good agreement with theoretical ones.

A switched capacitor oscillator with precision amplitude control and guaranteed start-up

A description is given of the design and performance characteristics of a precision switched capacitor (SC) oscillator. Features of this circuit include precision control over both frequency and amplitude, as well as means to ensure that oscillations start regardless of power-up sequence, reasonable offsets, etc. Many attributes of this oscillator are obtained by exploiting the unique properties of switched capacitor circuits; the proposed circuit does not possess a direct active-RC counterpart. The authors include derivations of analytical expressions for output frequency, amplitude, and harmonic distortion.

New Rc-Active oscillator configuration employing unity-gain amplifiers

A new sinusoidal oscillator configuration is proposed which employs op-amps as unity-gain amplifiers. The proposed circuit offers independent single-element controls for adjusting the condition of oscillation and oscillation frequency and has very good frequency stability. Practically, the circuit works well over a frequency range much higher than possible with other known types of oscillators (which use op-amps as ±K-gain or infinite-gain VCVSs). The proposed configuration also provides useful prototypes to derive novel switched-capacitor oscillators.

Continuous and switched-capacitor multiphase oscillators

This paper presents novel designs of multiphase oscillators. These oscillators generate n symmetric signals, i.e., equal in amplitude and equally spaced in phase, which have a wide range of applications in communications and signal processing. First, multiphase oscillators based on active sequence discriminators (SD's) are proposed. Then multiphase oscillators based on the SD and two-integrator-loop circuits containing only capacitors, switches, and op amps are derived. In addition to the fact that these switched-capacitor oscillators (SCO's) are easily constructed in IC form using MOS technology, they are shown to possess other attractive features. The input to the switched-capacitor (SC) circuit is a clock and the output is a sampled-and-held sinusoid of a frequency that is related to the clock frequency by an arbitrarily chosen capacitor ratio. The oscillation frequency follows linearly a continuously varying clock. Thus there is no need to vary any of the oscillator components to change the oscillation frequency. Ultralow oscillation frequencies can be generated using practical component values. The harmonic content can be made very small by increasing the number of samples in each oscillation cycle. Also, the amplitude stabilization and control circuitry with excellent settling properties are presented. It is shown that the complexity of the amplitude stabilization circuitry does not increase with the number of oscillator phases in the SD oscillator design. Experimental results using both the continuous and SC realizations are given which are in agreement with the theory presented.

Micropower switched-capacitor oscillator

A CMOS sinusoidal integrated oscillator based on a switched-capacitor third-order phase-shift network is described. Frequency is proportional to that of a clock, but may be controlled by a voltage. Accuracy is a few percent for a power consumption below 0.1 /spl mu/W in the audio range.