Oscillators – Automatic frequency stabilization using a phase or frequency... – Particular error voltage control
Patent
1996-12-06
1998-05-12
Grimm, Siegfried H.
Oscillators
Automatic frequency stabilization using a phase or frequency...
Particular error voltage control
331176, H03L 102, H03L 7085, H03L 718
Patent
active
057511942
DESCRIPTION:
BRIEF SUMMARY
This application is a national phase of international application PCT/F195/00320, filed Jun. 5, 1995.
The present invention relates to a method for controlling a phase-locked loop, which loop comprises a phase comparator, a charge pump, a loop filter and a voltage-controlled oscillator, and in which method the loop is provided with information on the measurement result of external temperature.
The operation of phase-locked loops is sensitive to variations in external temperatures, as is usually the case with electronic components and devices. Phase-locked loops are used, for example, in base stations and subscriber telecommunication terminals whose operation conditions vary greatly.
Phase-locked loops are designed and their adjustment is carried out, if possible, in such a way that when a loop moves from one frequency to another, the lock-in time of the loop onto the new frequency would be as short as possible. Best results are obtained, if loop adjustment is critically attenuated. In such a case, frequency error decreases fastest and the lock-in time is minimized. In phase-locked loops, variations in temperature cause the dynamic response of the loop to change. In cases the dynamic response changes due to variations in temperature, the adjustment either becomes supercritical or subcritical which results in an increase in the lock-in time.
The aforementioned phenomenon is especially problematic in systems which utilize frequency hopping, such as a cellular radio network, in which the frequency used changes time-slot-specifically. In the prior art solutions, it is well known to implement frequency hopping as a so-called baseband hopping in which a frequency synthesizer remains on a fixed frequency and does not change frequency time-slot-specifically. In cases frequency hopping synthesizers are used, the aim is to stabilize the lock-in time by an analog coupling in which the amplification of the operational amplifier of the loop filter is temperature controlled.
The drawback of baseband frequency hopping is that its implementation in a base station of a cellular radio network requires complete units and several transceivers in the base station. The number of hopping frequencies, however, is restricted to the number of transceivers. It is not possible to apply said method in a subscriber telecommunication terminal.
The dynamic response of a phase-locked loop is determined by a phase comparator, a loop filter and a voltage-controlled oscillator all of which are temperature dependent components. Furthermore, temperature dependent behaviour varies from one frequency of the voltage-controlled oscillator to another. For this reason, it is very difficult to perform temperature dependent amplification adjustment of a loop filter by an analog coupling, and to perform adjustment by both temperature and frequency is virtually impossible.
It is thus an aim of the present invention to implement an adjustment of a phase-locked loop, which adjustment stays critically attenuated in the required temperature range. Thus, by a method in accordance with the invention it is possible to minimize the lock-in time when moving from one frequency to another regardless of variations in temperature.
This is obtained by a method described in the introductory section, characterized in that the output signal of the charge pump is controlled on the basis of external temperature and the frequency being monitored.
The invention further relates to a phase-locked loop which comprises a phase comparator, a charge pump, a loop filter and a voltage-controlled oscillator, and which loop has measurement information on external temperature as an input. It is characteristic of a phase-locked loop of the invention that the loop comprises a means for controlling the output signal of the charge pump on the basis of the external temperature and the frequency being monitored.
The method of the invention enables temperature compensation of a frequency hopping synthesizer without external components. The method of the invention and the phase-locked loop can
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patent: 5173665 (1992-12-01), Norimatsu
patent: 5477194 (1995-12-01), Nagakura
Van Paemel, Mark, Analysis of a Charge-Pump PLL; A New Model, IEEE Transactions On Communications, vol. 42, No. 7, Jul. 1994. pp. 2490-2498.
Gardner, Floyd M., "Charge-Pump Phase-Lock Loops", IEE Transactions On Communications, vol. com-28, No. 11, Nov. 1980. pp. 1849-1858.
Dekker Andre
Haapanen Mika
Grimm Siegfried H.
Nokia Telecommunications Oy
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