Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Rectangular or pulse waveform amplitude control
Reexamination Certificate
1999-01-25
2001-05-22
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Rectangular or pulse waveform amplitude control
C327S108000, C327S172000
Reexamination Certificate
active
06236252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention is that of devices for generating current pulses, also known as charging pumps.
To be more precise, the invention concerns a low-noise device for generating current pulses.
The invention applies in particular, although not exclusively, to generating low-noise current pulses for a phase comparator included in a synthesizer of a radiocommunication terminal.
2. Description of the Prior Art
A device of the above type generally comprises current pulse generator means cooperating with polarizer means. The polarizer means supply a polarization voltage to the current pulse generator means.
There are two major families of current pulse generator devices according to the basic structure formed by the polarizer means and the current pulse generator means. The basic structure is either of the switched current mirror type or of the cascode current source type.
A switched current mirror current pulse generator device generally generates current pulses by switching switch means &phgr; and {overscore (&phgr;)} (see
FIG. 1
) at a frequency depending on the required frequency of the pulses. A current pulse is generated in two successive phases. In a first phase the switch means &phgr; are closed and the switch means {overscore (&phgr;)} are open to cause current to flow to the output (at the source of the transistor of the current pulse generator means). In this first type of device the algebraic value of the current corresponds to that of the current leaving the source of the transistor of the polarizer means. In a second phase the switch means &phgr; are open and the switch means {overscore (&phgr;)} are closed to prevent the flow of current. To generate a stream of current pulses the two phases are repeated at a frequency equal to that required for the output current pulses and corresponding to that imposed by the opening and closing of the switch means.
The cascode current source current pulse generator device generates current pulses by switching the switch means {overscore (&phgr;)} alone (see
FIG. 2
) at a frequency depending on the required frequency of the pulses. In a first phase the switch means {overscore (&phgr;)} are open allowing current to flow at the output (at the source of the cascode transistor). During a second phase the switch means {overscore (&phgr;)} are closed to prevent the flow of current at the output. To generate a stream of current pulses the two phases are repeated, as in the first type of device, at a frequency equal to the required frequency of the output current pulses and corresponding to that imposed by the switching.
However, the polarizer means of the above two types of current pulse generator devices generate undesirable noise. The components of the polarizer means do not exhibit ideal behavior and therefore generate noise. Such noise (in particular that due to the current source or sources and that due to the imperfections of the various components of the polarizer means) is recovered by the current pulse generator means and also transmitted on the output side of those means, possibly amplified.
Also the polarizer means are subject to power supply rejection that is equally problematic. Insufficient power supply rejection disturbs the operation of most of the components on the output side of the polarizer means.
A prior art solution aimed at reducing noise consists in isolating the power supplies of the system using them. A solution of this kind is not satisfactory because it is not readily compatible with an integrated system. There remain high levels of coupling within the system, generating interference.
Another prior art solution is to use a low charge injection logic circuit. This solution is also relatively disadvantageous because it is not readily compatible with a system whose overall size is to be reduced. A low charge injection logic circuit of the above kind necessitates the addition of new components.
One objective of the present invention is to alleviate the various drawbacks of the prior art.
To be more precise, one objective of the present invention is to provide a current pulse generator device which can be integrated into the system using it.
An additional objective of the invention is to provide a device of the above kind that strongly reduces or even eliminates the various kinds of noise generated by the polarizer means.
Another objective of the invention is to provide a device of the above kind that is simple to manufacture.
An additional objective is to provide a device of the above kind optimizing the costs of manufacture.
SUMMARY OF THE INVENTION
The above objectives, together with others that will become apparent hereinafter, are achieved in accordance with the invention by means of a current pulse generator device comprising current pulse generator means and polarizer means supplying a polarization voltage to said generator means wherein said device further comprises maintaining means for maintaining said polarization voltage to said generator means said maintaining means connected via switch means to said polarizer means, where said switch means can assume the following two positions in succession:
a closed or adjustment position in which said switch means connect said maintaining means to said polarizer means so that said maintaining means acquire said polarization voltage supplied by said polarizer means,
and an open or operating position in which said switch means isolate said maintaining means from said polarizer means, said maintaining means supplying to said generator means said previously acquired polarization voltage so that said generator means generate at least one low-noise current pulse.
The general principle of the invention is therefore based on isolating the polarizer means from the current pulse generator means when a pulse must be generated.
In other words, transmission of the noise generated by the polarizer means is prevented.
In this way the invention proposes a simple architecture that can easily be integrated into the system using it.
Note that the introduction of the maintaining and switch means is relatively low in cost.
Said polarizer means and said generator means advantageously together form a basic structure constituting either a switched current mirror or a cascode current source.
Thus the present invention can be implemented using the two major families of current pulse generator devices.
In an advantageous variant of the invention said basic structure is duplicated so that positive pulses and/or negative pulses can be generated. Clearly the present invention can be put into practice regardless of modifications known in themselves made to the basic structures.
In a first preferred embodiment of the invention said maintaining means comprise at least one capacitive component.
In a second preferred embodiment of the invention said maintaining means comprise in part the gate capacitance of an MOS transistor in said generator means.
Compared to the first embodiment, this feature has the advantage of not requiring any additional component for a cascode current source type basic structure.
Said switch means advantageously comprise at least one switching transistor.
Clearly any switching device known in itself can be used.
In one particular embodiment of the invention said switch means further comprise at least one filter resistor shunting said at least one switching transistor.
The resistor shunting the switching transistor therefore cooperates with the capacitive component of the maintaining means to filter the noise.
This feature also reduces the number of pulses required to reach the required amplitude of the current. In other words, it enables faster starting. When an MOS (metal oxide semiconductor) transistor is used as the switch means, spurious components of the transistor prevent ideal switching. The resistor shunting the switching transistor alleviates the greater part of the effects of such spurious components.
This also enables a single acquisition and therefore a single adjustment phase.
The invention also concer
Genest Pierre
Yang Fuji
Alcatel
Callahan Timothy P.
Englund Terry L.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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