Browse Prior Art Database

Current Division Based Delay Cell for Wide Frequency Range Voltage Controlled Oscillators

IP.com Disclosure Number: IPCOM000012806D
Original Publication Date: 2003-May-28
Included in the Prior Art Database: 2003-May-28
Document File: 5 page(s) / 52K

Publishing Venue

Motorola

Related People

Guilebaldo Gutiérrez Chávez: AUTHOR [+3]

Abstract

This paper deals with a differential delay cell based on the current division principle used for the implementation of a wide frequency range voltage controlled ring-oscillator. The frequency range is adjusted by controlling both the current flowing through the delay cell output and by the amount of delay cells used in the voltage controlled ring-oscillator.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Current Division Based Delay Cell for Wide Frequency Range Voltage Controlled Oscillators

Guilebaldo Gutiérrez Chávez, Sergio A. Solís Bustos, and Jesús L. Finol

Abstract

This paper deals with a differential delay cell based on the current division principle used for the implementation of a wide frequency range voltage controlled ring-oscillator. The frequency range is adjusted by controlling both the current flowing through the delay cell output and by the amount of delay cells used in the voltage controlled ring-oscillator.

1. Introduction

Wide frequency range Voltage Controlled Oscillators (VCOs) are mainly used in applications such as, frequency synthesizers and Radio Frequency (RF) circuits. Delay cell based VCOs have been successfully employed in these applications. Basically, there are two types of delay cells; differential pair based and inverter based both of them with a great variety of topologies. In this document, a differential delay cell, which uses two coupled differential pairs connected to a common current source, is presented. The cell is based on the current division principle used to control the current flowing into the output, thus the cell's delay is adjusted. This approach enables us to achieve a wide frequency range when used in a VCO either by adjusting the delay of each cell or by changing the number of delay cells used within the VCO.

The publication is organized as follows. The basic operation principle is discussed in section 2. The section 3 shows the simulation results for a four-stage VCO. In section 4 further applications for the delay cell are briefly described. Finally, in section 5 the conclusions are addressed.

2. Basic Delay Cell

The cell operates by controlling the current flow through different transistors. The current source, Ibias (see figure 1), must be kept constant for the entire operation range.

For low control voltages (vc - vcb < 0) most of the current flows through the transistors M3, M4, M9 and M10. These transistors will be called outer branch for future reference.

For high control voltages (vc – vcb > 0) most of the current flows through the transistors M1, M2, M7, M8, M11, M12, M13, M14, and M15. These transistors will be called inner branch for future reference.

As the control voltage increases from values below zero to values above zero, the current flow diminishes in the outer branch and increases in the inner branch. This is the basic idea behind the current division.

To keep linear the current division, the Ibias must drive the same load. In other words, load variations must be minimized while the current division occurs. Because current division linearity is highly dependent on Ibias then, Ibias should be designed to minimize its variations due to changes in the fabric...