Oscillators – Automatic frequency stabilization using a phase or frequency... – Particular error voltage control
Reexamination Certificate
2000-02-18
2002-04-30
Kinkead, Arnold (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Particular error voltage control
C455S260000, C455S226100, C455S226200
Reexamination Certificate
active
06380809
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to tuning of a local oscillator, and more particularly, to a method for increasing the speed with which a local oscillator tunes to a predetermined frequency in order to more quickly step through a set of power measurements on a number of neighbor list stations.
2. Description of Related Art
Within a digital mobile station, there is a need to be able to adjust the local oscillator to a predetermined frequency as quickly as possible when stepping through a set of power measurements on neighbor list stations. By quickly stepping through the frequencies on which power measurements are made the mobile station hardware may be turned off for longer periods of time once the power measurements are completed. This saves battery charge and provides longer operating periods for a mobile station operating solely on battery power.
A conventional, prior art mobile station
10
is shown in FIG.
1
. The mobile station
10
includes a controller
12
which controls the functions of the mobile station
10
. The controller
12
typically includes a central processing unit (CPU) (not shown), memory (not shown), and I/O ports (not shown). The controller
12
processes voice or data signals to and from a transceiver
14
. The transceiver
14
converts a voice or data signal from the controller
12
to a radio wave and also detects and demodulates a received radio wave into a voice or data signal. The transceiver
14
is connected to an antenna
16
for transmission and reception of radio waves.
The controller
12
is also connected to a microphone
18
, speaker
20
and user interface
22
. The microphone
18
includes a dynamic microphone, condenser microphone, or the like, to transduce a user's voice into an electrical signal. An analog to digital converter (ADC) (not shown) converts the electrical signal into a digital voice signal. The speaker
20
outputs a received voice signal, and typically includes a digital-to-analog converter (DAC) (not shown) and amplifier (not shown). The user interface
22
includes a display, such as an LED or LCD, and a keypad or other controls. A rechargeable battery
24
provides power to the mobile station
10
.
A synthesizer
26
is connected to the controller
12
and transceiver
14
. The synthesizer
26
generates signals at variable frequencies in response to an input frequency value from the controller
12
. The generated signals are communicated to the transceiver
14
for reception or transmission of a channel about that frequency. The synthesizer
26
includes a phase detector
28
, loop filter
30
, and voltage controlled oscillator (VCO)
32
. A reference crystal
34
is connected to the synthesizer
26
and generates a reference signal
35
at a set frequency f
r
. The controller
12
controls the frequency output of the synthesizer
26
by transmitting a channel data signal
11
to the synthesizer
26
to store a divisor N value in a Divide-by-N Register
36
. The controller
12
then transmits a control signal
13
to the synthesizer
26
to latch the divisor N value. In response, a frequency f
o
of output signal
33
from the VCO
32
is divided by N. The phase detector
28
compares the phases of the output signal
37
of the Divide-by-N Register
36
and the reference signal
35
from reference crystal
34
to generate an error voltage (V
e
) signal
29
proportional to the phase difference between the two signals. The loop filter
30
is a low pass filter that filters the voltage error V
e
, signal
29
prior to inputting the signal to the VCO
32
. The frequency f
o
of the output signal
33
of the VCO
32
stabilizes to f
o
=N*f
r
and is transmitted to the transceiver
14
.
The conventional operation of the mobile station
10
of
FIG. 1
during a measurement operation of a set of channels is now described. The mobile station
10
receives a measurement order or a neighbor cell list from the radio base station
4
over a traffic or control channel. The controller
12
waits until the next idle state to perform measurements of the channels designated. During the next idle period, the controller
12
determines the number of channels to measure. The controller
12
stores data for the first channel to be measured in the Divide-by-N Register
36
of the synthesizer
26
and transmits a “latch new channel data” signal
13
to the synthesizer
26
. In response, the synthesizer
26
generates a VCO output signal
33
at a frequency f
o
specified by the channel data in the Divide-by-N Register
36
. The VCO output signal
33
is communicated to the transceiver
14
which then receives a measurement command
15
from the controller
12
. The transceiver
14
measures the signal strength of the first channel and transmits a measured signal strength data signal
17
to the controller
12
.
The controller
12
receives the measured signal strength data and decrements the number of channels to measure. The controller
12
determines if additional channels are to be measured. If no more channels are to be measured, the controller
12
again enters an idle period and is ready to transmit or receive on a traffic channel or an active state. Otherwise, the controller
12
loads the channel data for the next channel to be measured into the synthesizer
26
. If there is not sufficient time to complete the measurements during the idle period between transmitting or receiving, the mobile station
10
must wait until the next idle period to continue the measurements.
The power measuring operation in a mobile station needs to be performed quickly and efficiently, especially when a mobile station is measuring channels during an idle period, since there is limited time to perform the operation. The process normally taking up the greatest amount of time is the tuning of the local oscillator
32
to the frequency being measured. A need has thus arisen in the industry for a more efficient manner for tuning an oscillator to enable faster measurement of varying sets of channels in a neighbor list by a mobile station.
One solution involves the use of so-called speedup mechanisms within the phase locked loop of the mobile station. These mechanisms push additional charge current into the phase locked loop in an effort to more quickly adjust the frequency of the oscillator. However, this method has an inherent limit on how fast the frequency can change before effects of changing the loop gain cause longer settling transients within the phase locked loop. Thus, an improved method for more quickly tuning a local oscillator signal to a desired frequency in order to more rapidly step through power measurements for neighbor list of mobile stations is needed.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing and other problems with a method and apparatus for more quickly tuning an oscillator to a selected frequency within a mobile station during power measurements. A switch, controller and associated analog to digital and digital to analog converters are located between an output of a phase locked loop and the voltage control input of a local oscillator. The phase locked loop consists of all the parts of the synthesizer and reference crystal less the voltage controlled oscillator. The switch has a first and second positions. In the first position, the output of the phase locked loop is passed directly to the voltage control input of the local oscillator. In the second position, an output from the controller, via a digital to analog converter, is provided to the voltage control input of the local oscillator.
In response to a request to perform power measurements on frequencies for members of a neighbor list within a mobile station, an initial determination is made by the controller as to whether the local oscillator has previously tuned to the requested frequency. If not, the switch is place in the first position such that the voltage control signal applied to the local oscillator comes from the phase locked loop. During this time, the applied voltage c
Coats & Bennett PLLC
Ericsson Inc.
Kinkead Arnold
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