Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
1998-03-27
2001-01-30
Tsang, Fan (Department: 2746)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S136000, C455S164100, C455S173100, C455S182200, C455S192100, C455S258000, C455S260000, C455S264000, C372S038060, C372S038060, C327S047000, C327S175000
Reexamination Certificate
active
06181923
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to, for example, automatic frequency control circuit and method of automatic frequency control preferable for use with portable telephone terminal.
(2) Description of the Related Art
Generally, automatic frequency control circuit (AFC circuit) is a circuit which controls reference frequency in the synthesizer (received local generation unit) of terminal station (portable station) according to the quantity of a drift, after counting stable terminating frequency from the base station, when a drift with predetermined theoretical value exists. Also, terminating frequency is configured to be counted at the point of received intermediate frequency signal (hereinafter called as received IF signal).
Because the status of radio wave at the portable station (portable telephone terminal) is always changing by receiving fading phenomena, and etc., to average these effects, sufficient counting time is necessary for precise measurement. On the other hand, the equipment, like a digital portable telephone, which operates with TDMA (Time Division Multiple Access) system during receiving period, can only measure frequency of receiving slot of itself during TDMA operation (that is, during conversation), thus, longer counting time is also necessary for sufficient counting process. Therefore, a longer time (T/S)×F becomes necessary, where T is a time, F is a time of one frame, and S is a time of the receiving slot of itself.
Because of this, in portable station, there are many cases counting not received IF signal itself, but reference carrier of detected signal which is regenerated in the demodulator circuit (DEM circuit) in receiving unit of portable station. That is to say, because influence of fading is suppressed, regenerative carrier signal can be counted more precisely within short period of time than counting received IF signal directly.
However, as stated above, in case of automatic frequency control circuit counting reference carrier of detected signal regenerated in demodulator circuit, the limit of frequency follow up of the demodulator circuit becomes the limit of frequency follow up of the automatic frequency control circuit itself. That is to say, the demodulator circuit, in most cases, is simplified as not to be equipped with unnecessary circuit other than enough circuit for detection, in order to reduce the scale of the circuitry, and to easily integrate in large scale. Therefore, frequency limit of follow up as stated above has been produced. In certain instances, there may be some cases when the frequency limit of follow up will theoretically be produced by the detection system.
Specifically, as shown in
FIG. 9
, the carrier regeneration circuit which is configured with the digital circuit of demodulator circuit has the limit of follow up range [“−FL~+FL” (2|FL|) cf. A in FIG.
9
] against input frequency (received IF frequency). With the input frequency which is out of this limit of follow up range, output frequency (regenerative carrier frequency) repeats identical value. Therefore, in the area out of the limit of follow up range, ratio of value between output frequency and input frequency does not coincide with. On the other hand, when a synthesizer using highly stable local oscillator is equipped in portable station, this synthesizer becomes expensive, and the total cost of whole portable station will be boosted in turn.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an automatic frequency control circuit and a method of automatic frequency control, which is able to expand follow up range of the automatic frequency control circuit, by employing a circuit which directly counts the received signal and a circuit which counts regenerative carrier signal in combination.
Therefore, the automatic frequency control circuit according to the present invention is characterized in that, the automatic frequency control circuit processing frequency control of the received signal frequency based on the incoming received signal, comprising; a first control circuit for processing frequency control based on precision counter by using above mentioned incoming received signal; and a second control circuit for processing frequency control based on coarse counter by using above mentioned incoming received signal; wherein above mentioned first control circuit and above mentioned second control circuit are used interchangeably in response to the incoming received signal.
Moreover, the automatic frequency control circuit according to the present invention is characterized in that, the automatic frequency control circuit processing frequency control of the received signal frequency based on the incoming received signal, comprising; a first counter for counting frequency of regenerative carrier signal which is generated based on above mentioned incoming received signal; a second counter for counting frequency of above mentioned incoming received signal; a first reference value setting circuit having first reference value for regenerative carrier signal; a second reference value setting circuit having second reference value for received signal; a first comparator for comparing the first reference value outputted from above mentioned first reference value setting circuit with the output of above mentioned first counter; a second comparator for comparing the second reference value outputted from above mentioned second reference value setting circuit with the output of above mentioned second counter; a selection circuit for selecting either of output from above mentioned first comparator and output from above mentioned second comparator; a frequency control signal generation unit for outputting frequency control signal for processing frequency control of above mentioned received signal frequency based on the output of the selection circuit; a control signal output unit for outputting selective switching control signal in response to incoming received signal.
In addition, the automatic frequency control circuit according to the present invention is characterized in that, the automatic frequency control circuit, wherein above mentioned frequency control signal generation unit comprises; a control pulse generation circuit for generating control pulse signal based on output from above mentioned selection circuit; and an up/down counter for outputting frequency control signal by increasing or decreasing count value in response to control pulse signal from the control pulse generation circuit.
Moreover, the automatic frequency control circuit according to the present invention is characterized in that, the automatic frequency control circuit, wherein above mentioned control signal output unit comprises; a selection control signal generation unit for outputting selection control signal for selecting either of output from above mentioned first comparator and output from above mentioned second comparator; and a gate generation circuit for outputting each of the counting time in above mentioned first counter and in above mentioned second counter based on the selection control signal from the selection control signal generation unit.
Therefore, according to the automatic frequency control circuit of the present invention, when drift of received frequency exceeds the limit of follow up of the demodulator circuit, the frequency of the regenerative carrier signal can be controlled within the limit of follow up range, by counting the received IF signal directly using auxiliary counter, thus the follow up range of the automatic frequency control circuit can be expanded, and the processing capability is greatly increased.
In addition, the automatic frequency control circuit according to the present invention is characterized in that, the automatic frequency control circuit processing frequency control of the received signal frequency based on the incoming received signal, comprising; a selection circuit for selecting either of the frequency of regenerative carrier signal gene
Inagami Fujio
Kawano Osamu
Fujitsu Limited
Helfgott & Karas P.C.
Nguyen Simon
Tsang Fan
LandOfFree
Automatic frequency control circuit and method of automatic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Automatic frequency control circuit and method of automatic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Automatic frequency control circuit and method of automatic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2450736