Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synchronizing
Reexamination Certificate
2000-07-24
2004-05-11
Nguyen, Linh M. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synchronizing
C327S157000, C327S148000
Reexamination Certificate
active
06734708
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a current source circuit and phase locked loop equipped with such a circuit, by means of which the phase angle of an output signal is controlled with respect to the phase angle of a reference signal, if required with a desired phase offset.
The general design of such phase locked loops is known from “IEEE Transactions on Communications”, Vol. COM-28, No. 11, November 1980: “Charge-Pump Phase-Lock Loops” by F. M. Gardner, pages 1849 to 1858, where a current source circuit (charge pump) is connected between the outputs of a phase detector and a loop filter which controls an oscillator and contains a capacitance, and this current source circuit feeds the loop filter with current or draws current from the loop filter depending on the respective phase comparison result.
The general design of such phase locked loops is also known from “IEEE Journal of Solid-State Circuits”: “A 2.7-V GSM RF Transceiver IC”, Yamawaki et al, Vol. 32, No. Dec. 12, 1997, pages 2089-2096, in which the output signal of the oscillator whose phase is to be controlled is applied, after mixing with the local signal, to the phase comparator, to whose other input a reference signal in the form of an intermediate frequency signal is applied. A current source circuit is connected between the output of the phase comparator and the loop filter which actuates the oscillator, and this current source circuit contains transistor switches in the same way as in the document already discussed, which switch the current supply of the loop filter as a function of the respective phase angle, so that the loop filter capacitance is either charged or discharged. However, the switching of the driver transistors (charge pumps) is in each case associated with switching interference signals so that the overall signal-to-noise ratio deteriorates owing to the switching processes carried out by the driver transistors. In addition, the required circuit complexity is rather high owing to the switching transistors and their circuitry.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a current source circuit, in particular for a phase locked loop, in which the number of switching processes is reduced, and the signal-to-noise ratio is thus improved.
This object is achieved by the features cited in patent claim 1. Furthermore, a phase comparator is provided, according to claim 7. Advantageous refinements of the invention are specified in the dependent claims.
Only a single switch is now provided in the current source circuit according to the invention, which is switched as a function of a control signal, for example the phase comparison result, and either charges or discharges the component connected on the output side, for example a loop filter. The other function, that is to say the discharging or the charging of the component, is carried out by a continuously switched-on driver transistor. In consequence, this driver transistor does not carry out any switching processes and thus produces no switching noise. The total switching noise produced is thus reduced, and the signal-to-noise ratio is improved. The circuit also provides the advantage that the component which produces the control signal, for example the phase comparison circuit, now need be equipped with only a single output, to which the driver switch is connected, being switched as a function of the control signal, for example the phase comparison result. The required circuit and wiring complexity is thus also reduced at the same time.
The continuously switched-on driver stage is preferably designed in such a way that it carries a current which differs from the current carried by the switched driver stage when it is switched on. This results in a net current difference which acts as a bias current and is used for frequency coverage during a search and lock-on process. In consequence, the circuit design is even further simplified. Yet another simplification can be achieved by the continuously switched-on driver stage being part of a current mirror circuit into which a desired stabilized current flows. This current mirror circuit is preferably also connected to the phase comparison circuit and causes a stabilized current to flow into it.
The total number of circuits and control components required is thus reduced, so that temperature drift problems, matching problems and the like are also reduced. Good circuit characteristics are thus ensured.
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Floyd M. Gardner: “Charge-Pump Phase-Lock Loops”, IEEE Transactions on Communications, vol. COM-28, No. 11, Nov. 1990, pp. 1849-1858.
Taizo Yamawaki et al.: “A 2.7-V GSM RF Transceiver IC”, IEEE Journal of Solid State Circuits, vol. 32, No. 12, Dec. 1997, pp. 2089-2096.
Herrmann Helmut
Herzinger Stefan
Zhang Xiaopin
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Nguyen Linh M.
Stemer Werner H.
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