Multiphase receiver and oscillator

Details Multiphase receiver and oscillator Multiphase receiver and oscillator

1998-03-04

2002-05-07

Chang, Vivian (Department: 2682)

Telecommunications

Receiver or analog modulated signal frequency converter

Frequency modifying or conversion

C455S205000, C331S057000, C331S045000, C327S238000, C375S332000

Reexamination Certificate

active

06385442

ABSTRACT:

BACKGROUND OF INVENTION
The present invention relates to radio transmitters and receivers, and to oscillators for use therein. In particular, the present invention, in its various aspects, addresses problems that arise in connection with designing and fabricating radio circuits on integrated circuit chips, and particularly on CMOS integrated circuit chips.
FIG. 1
discloses a known technique for reception of Amplitude-Shift-Keyed (ASK) radio signals using a local oscillator having quadrature phase components, including systems for direct conversion to baseband. In the receiver
10
, a modulated carrier signal, x(t), is provided on input line
12
to mixers
14
and
16
. The mixers multiply the modulated carrier x(t) by two local oscillator signal components in phase quadrature, to thereby detect in-phase and quadrature-phase components of the received signal at the intermediate frequency (IF). The in-phase and quadrature-phase components of the received signal at IF are isolated from the mixers' (
14
and
16
) outputs by low-pass filters
18
and
20
. The instantaneous signal energies of the in-phase and quadrature-phase components of the received signal at IF are detected by energy detectors
22
and
24
. The detected in-phase and quadrature-phase instantaneous signal energy outputs are summed in combiner
26
to produce an output signal J representative of the instantaneous baseband signal energy, which is independent of the phase relation between the local oscillator and the transmitted carrier. In amplitude-shift-keying systems, the instantaneous baseband signal energy is also representative of the original baseband signal which modulates the transmitted carrier. Hence, the demodulation process is achieved.
One difficulty associated with using a detector having the arrangement of
FIG. 1
is the requirement of providing local oscillator signal components having quadrature-phase relation.
FIG. 2
illustrates one possible arrangement for providing quadrature phase components of a local oscillator in an integrated circuit configuration. The oscillator
30
of
FIG. 2
comprises a four-stage differential ring oscillator having differential amplifiers
32
,
34
,
36
and
38
. The circuit of
FIG. 2
oscillates with period equal to the total time delay of the four differential amplifiers. The time delay of each differential amplifier can be varied, thereby to change the frequency of oscillation, by providing a voltage control on lead
40
which changes the propagation delay through each of the differential amplifiers. Since the total phase delay around the loop in the differential ring oscillator
30
is 360°, quadrature local oscillator signal components can easily be obtained at the outputs of adjacent differential amplifiers, such as amplifiers
32
,
34
, as shown in FIG.
2
.
The oscillator of
FIG. 2
can be difficult to implement where the required oscillation frequency is relatively high, such as 2.4 GHz allocated to the unlicensed ISM (Industrial, Scientific and Medical) frequency band. In attempting to implement differential ring oscillator
30
using CMOS technology, it has been found that the maximum frequency available with four stages is about 1.9 GHZ. Differential ring oscillator
30
can be implemented with three differential amplifier stages, but such arrangement will not provide the quadrature or orthogonal phase local oscillator components required in the receiver
10
of FIG.
1
.
FIG. 3
is a graph showing the relation of the control voltage V for the oscillator
30
to the operating frequency. Typically, small variations in the control voltage &Dgr;V, can produce significant variations in the frequency of the oscillator output. Where the control voltage has a periodic component, as may arise by reason of leakage of a reference oscillator signal in a phase locked loop, the resulting variation in control voltage V will produce undesired FM sidebands in the output signal of oscillator
30
.
FIG. 8
discloses a classic quadrature direct-conversion technique for reception of frequency modulated (FM) radio signals. In the receiver
120
, a modulated carrier signal, x(t), is provided on input line
122
to mixers
124
and
126
. The mixers multiply x(t) by two local oscillator signal components in phase quadrature, to thereby detect in-phase and quadrature-phase components of the received signal at the intermediate frequency (IF). The in-phase and quadrature-phase components of the received signal at IF are isolated from the mixers' (
124
and
126
) outputs by low-pass filters
128
and
130
. The frequency modulation of the in-phase and quadrature-phase components of the received signal at IF are detected by differentiators
132
and
134
. The detected in-phase and quadrature-phase frequency modulation outputs are multiplied in mixers
136
and
138
by the quadrature-phase and in-phase components, respectively, of the low-pass filtered received signal at IF and then are summed in combiner
140
to produce an output signal y(t) representative of the demodulated frequency deviation. The in-phase and quadrature-phase components of the received signal at IF are also each squared in detectors
142
and
144
and then summed in combiner
146
to produce an output signal J(t) representative of the instantaneous received signal energy, which is independent of the phase relation between the local oscillator and the transmitted carrier.
It is an object of the present invention to provide a radio frequency receiver which can be implemented in an integrated circuit without suffering from the disadvantages of the art.
It is a farther object of the invention to provide an integrated circuit oscillator having an improved suppression of undesired FM sidebands in the oscillator output.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided an amplitude-modulated signal receiver including a local oscillator providing at least three equally-phased local oscillator signal components. The local oscillator signal components are mixed with a modulated carrier signal and the resultants are provided to corresponding signal detectors. The output of the signal detectors are combined to provide a received signal,
In accordance with the present invention the local oscillator may be implemented as a voltage-controlled oscillator in a phased-locked loop. The voltage-controlled oscillator has a frequency which is controlled by first and second current control devices, including coarse and fine current control devices. Preferably the coarse current control device is controlled by a signal which is selected in discrete steps, while the fine current control device is controlled by an analog signal.
The phase locked loop may include signal comparators for comparing a phase error signal to upper and lower values to implement adjustments of the coarse control signal in discrete steps. The phase error signal is used for controlling the fine current control device.
In accordance with the invention, there is also provided a frequency-modulated signal receiver including a local oscillator having at least three equally phased components. Each of the phase components of the local oscillator is mixed with the received signal and the outputs of all but one of the mixers are additively combined. A discriminator responsive to the outputs of the one uncombined mixer and the combiner provides an output signal representative of the demodulated frequency modulation. Preferably, the discriminator includes a first differentiator responsive to the one uncombined mixer output, a second differentiator responsive to the combiner output, a first mixer responsive to the first differentiator output and the combiner output, a second mixer responsive to the second differentiator output and the one uncombined mixer output and a second combiner for combining the outputs of the first and second mixers.
In accordance with the invention, there is also provided a receiver for receiving phase modulated signals including the frequency modulated signal receiver and a device for integrating t

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