Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2000-11-29
2004-08-31
Nguyen, Simon (Department: 2685)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S165100, C455S168100, C455S183100, C455S188100, C455S552100, C331S002000, C331S179000
Reexamination Certificate
active
06785525
ABSTRACT:
The present invention relates to a multiband frequency generation with a PLL-circuit. In particular, the present invention relates to a multiband frequency generator to generate an output signal in a plurality of frequency bands and, further to a sending/receiving unit wherein the multiband frequency generator according to the present invention may be used.
FIG. 8
shows a typical method for sending and receiving signals in mobile phones. In the receiving path, a first mixer stage
204
comprising a multiplier
200
and a band pass filter
202
is supplied with a local oscillator signal outputted through a frequency generator
206
such that at the output of the mixer stage
204
the receiving signal is available according to a fixed intermediate frequency (IF) for the further processing in downstream circuit unit (not shown).
As also shown in
FIG. 8
, when sending a modulated sending signal (provided in the base-band) this sending signal is converted to an intermediate frequency-band specified through a sending intermediate frequency signal using a second mixer stage
208
with a second multiplier
210
and a second band-pass
212
. Then, the conversion to the sending channel is executed through a third mixer stage
218
comprising a third multiplier
214
and a third band-pass filter
216
.
FIG. 9
shows a detailed schematic diagram for the frequency generation unit
206
. Here, the object is to tune the frequency of a voltage-controlled oscillator
220
such that it is coincident to a frequency of a basic oscillator
222
multiplied with a dividing factor of a second programmer divider
228
. In
FIG. 9
, specific numerical values are given for a GSM-application example in square brackets.
The basic oscillator
222
comprises a reference oscillator
224
and in addition a first programmable divider
226
to variably pre-specify a reference frequency. A second programmable divider
228
is provided to convert the frequency generated by the voltage-controlled oscillator
222
into the pre-specified reference frequency outputted by the basic oscillator
222
.
A phase detector
230
enables a comparison of the sending signal converted with the second programmable divider
228
and the reference signal outputted through the first programmable divider
226
. The phase error between the divided reference signal and the divided output signal of the voltage-controlled oscillator
220
determined by the phase detector
230
is supplied to a loop filter
232
where an integration takes place.
Using this integrated error signal, the voltage-controlled oscillator
220
is controlled until there exists no further frequency and phase difference, respectively, between the signals used for comparison. Herethrough, the voltage-controlled oscillator
220
has a relative stability that is identical to the relative stability of the basic oscillator
222
. For the example shown in
FIG. 9
, e.g., in case the relative stability of the basic oscillator is (1 Hz)/(200 kHz) the relative stability for the voltage-controlled oscillator
220
is (3860 Hz)/(772 Mhz).
For applications such as GSM 900, GSM 1800 or PCS-mobile telephony, the tuning of the receiving or sending channel is carried out through determination of the divider ratio for the first and second programmable divider
226
and
228
, respectively. Therefore, the voltage-controlled oscillator
220
may easily be tuned to different sending frequencies within a stable operation. Here, the adjustment behaviour and the stability is essentially determined through the design of the loop filter
232
.
The design shown in
FIG. 9
is suitable for mobile phones being operated in one frequency band. However, this single-band operation is no longer suitable in view of the increasing number of subscribers and the limited number of sending frequencies in existing cellular mobile networks.
To the contrary, a combination of technical advantages being related to different approaches seems to be promising, in particular through providing multiband cellular networks and multiband mobile phones being related thereto, e.g., through combining the GSM 900, GSM 1800 and PCS frequency bands.
However, a prerequisite to this approach is the frequency generation for the respective frequency bands while simultaneously meeting the strict requirements explained with respect to
FIGS. 8 and 9
. For a dual band operation two frequency generators will be required for the two frequency bands. However, it is not possible to use only a single voltage-controlled oscillator since the tuning range that will be necessary in case of a single voltage-controlled oscillator would lead to an influence of noise onto the system that is too large and therefore to a violation of pre-defined specifications. Therefore, two voltage-controlled oscillators operating independently should be provided for the dual band operation mode.
The direct generalization of the approach explained with reference to
FIG. 9
would be a duplication of the components according to the number of pre-specified frequency bands. While this allows to provide frequency signals in an independent manner through related phase-locked loop circuits, this may only be achieved with significant additional circuitry and additional costs. Further, increased space requirements constitute a barrier against this approach, since a plurality of frequency synthesis units are necessary, e.g., in the form of a plurality of integrated circuits.
In view of the above, the object of the present invention is to provide a multiband frequency generator with minimized circuitry requirements.
According to the present invention, this object is achieved through a multiband frequency generator to generate an output signal in at least two frequency bands, comprising a voltage-controlled multiband oscillator to generate an output signal in each frequency band at one output for each frequency band, a frequency synthesis means to derive a phase difference between a control input signal for the frequency and the generated output signal, at least one control means for the voltage-controlled multiband oscillator using the phase difference generated through said frequency synthesis means as correcting or manipulating variable, respectively, wherein each output terminal of said multiband oscillator is coupled to the frequency synthesis means via a frequency selective coupling means.
Therefore, according to the present invention, only a single frequency synthesis means must be used since different output branches of the multiband frequency generator are always coupled to the same frequency synthesis means in a frequency selective way. The frequency selective behaviour of the coupling unit enables an excellent decoupling of the different single oscillator units of the voltage-controlled multiband oscillator.
Further, the invention enables a low loss between the different oscillator units of the voltage-controlled multiband oscillator and the phase-locked loop circuit comprising the frequency synthesis means and the control means.
Still further, the frequency selective coupling means also enables an impedance matching between the oscillator units of the voltage-controlled multiband oscillator and the phase-locked loop circuit and in addition a DC-decoupling.
According to a further preferred embodiment of the present invention, a control means is provided for each frequency band.
The provision of a single control means for each frequency band enables the individual determination of the adjustment behaviour and the stability of the different voltage-controlled oscillators.
According to a further preferred embodiment of the present invention, the voltage-controlled multiband oscillator comprises a plurality of voltage-controlled single band oscillators connected in parallel. Alternatively, there may be provided a switchable voltage-controlled oscillator. Both approaches enable the flexible handling of pre-defined specifications in that the number of voltage-controlled single band oscillators and switching stages of the switchable voltage-controlled oscillator
Nguyen Simon
Telefonaktiebolaget L M Ericsson (publ)
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