Communication transmitter using offset phase-locked-loop
A translational-loop transmitter generates RF signals using at most one phase-locked-loop (PLL) circuit. In one embodiment, a single PLL generates two local oscillation signals. The first oscillation signal is mixed with a baseband signal to generate an intermediate frequency signal. The second oscillation signal is input into the translational loop to adjust a voltage-controlled oscillator to the desired carrier frequency. In order to perform this type of modulation, the frequencies of the local oscillation signals are set so that they are harmonically related to one another relative to the carrier frequency. Other embodiments generate only one oscillation signal. Under these conditions, the intermediate frequency signal is generated using the oscillation signal, and a frequency divider in the translational loop is used to generate a control signal for adjusting the voltage-controlled oscillator to the carrier frequency. In still other embodiments, a transmitter signal is generated without using any phase-locked-loop circuits. This is accomplished by generating an intermediate frequency signal using a crystal oscillator, and then using a frequency divider in a feedback loop to generate a control signal for adjusting the voltage-controlled oscillator to the carrier frequency. By minimizing the number of phase-locked-loop circuits in the transmitter, the size, cost, and power requirements of mobile handsets may be significantly reduced.
1. A method for generating oscillation signals, comprising:
generating a first oscillation signal from a reference oscillation signal; and
generating a second oscillation signal from the reference oscillation signal;
wherein the first oscillation signal and the second oscillation signal relative are non-harmonically related relative to a desired carrier frequency, wherein the first oscillation signal is equal to
N
1
M
1
F
C
and the second oscillation signal is equal to
N
2
M
2
F
C
,
where F c is said desired carrier frequency, and wherein:
[
N
1
M
1
+
N
2
M
2
]
=
1
,
where
M
i
and
N
i
are
integer
numbers
,
N
i
M
i
×
K
≠
1
,
where
K
is
an
integer
number
and
i
is
an
integer
number
,
and
N
1
M
1
×
S
R
=
N
2
M
2
,
where
S
and
R
are
integer
numbers
.
2. The method of claim 1 , further comprising: mixing the second oscillation signal with a baseband signal to generate an intermediate frequency signal; and
setting a frequency of a voltage-controlled oscillator in a translational-loop based on the first oscillation signal, said frequency of the voltage-controlled oscillator corresponding to said desired carrier frequency.
3. The method of claim 1 , wherein the first oscillation signal and the second oscillation signal are generated from a single phase-locked loop device.
4. A system for generating oscillation signals, comprising:
a phase-locked-loop unit which generates a reference oscillation signal;
a local oscillator signal generator which generates a first oscillation signal and a second oscillation signal from the reference oscillation signal, wherein the first oscillation signal and the second oscillation signal are non-harmonically related relative to a desired carrier frequency, wherein the first oscillation signal is equal to
N
1
M
1
F
C
and the second oscillation signal is equal to
N
2
M
2
F
C
,
where F c is said desired carrier frequency, and
[
N
1
M
1
+
N
2
M
2
]
=
1
,
where
M
i
and
N
i
are
integer
numbers
,
N
i
M
i
×
K
≠
1
,
where
K
is
an
integer
number
and
i
is
an
integer
number
,
and
N
1
M
1
×
S
R
=
N
2
M
2
,
where
S
and
R
are
integer
numbers
.
5. The system of claim 4 , further comprising:
a first mixer which mixes the second oscillation signal with a baseband signal to generate an intermediate frequency signal; and
a translational-loop which receives an output of said first mixer, said translational-loop including a voltage-controlled oscillator having a frequency set based on the first oscillation signal, said frequency of the voltage-controlled oscillator corresponding to said desired carrier frequency.
6. The system of claim 5 , wherein said translation-loop includes:
a second mixer which mixes an output of the voltage-controlled oscillator with the first oscillation signal to produce a feedback signal; and
a phase/frequency detector which compares the feedback signal to the intermediate frequency signal to derive a control signal for setting the voltage-controlled oscillator to said desired carrier frequency.
7. The system of claim 4 , wherein the local oscillator signal generator generates the first oscillation signal and the second oscillation signal from a single reference oscillation signal, the single reference oscillation signal being output from a single phase-locked loop unit.