Active quadrature signal generator using load having...

Details Active quadrature signal generator using load having... Active quadrature signal generator using load having...

2002-06-24

2004-12-14

Nguyen, Minh (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Phase shift by less than period of input

C327S238000, C327S256000

Reexamination Certificate

active

06831497

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a semiconductor circuit, and more particularly to a circuit for producing poly-phase quadrature signals necessary in high frequency transmitter and receiver of a communication system, in which the quadrature signals are produced using the phase difference between a load having a low-pass filter characteristic and a load having a high-pass filter characteristic and the quadrature signal is then used in the differential structure to produce amplified signal having 4 quadrature phases.
2. Description of the Prior Art
In a digital communication system, generally, if the frequency band of a signal to be transmitted does not match with the property of a medium, it is required that the signal be moved to an adequate frequency band and then transmitted. Among modulation methods, as identifying the phase difference of 180° is much easier than identifying variations in the frequency, phase shift-keying (PSK) technique has been widely employed. In a modern high-speed communication system for processing a lot of data, quadrature phase shift-keying(QPSK) technique which four values can be identified by a single symbol with phase shift by 90° has been widely used. In this QPSK technique, the phase shift by 90° of a series of binary data pair can be generated by a pair of a mixer using a carrier wave of a cosine component and a mixer using a carrier wave of a sine component. At this time a poly-phase quadrature signal generator produces the quadrature signals of sine wave and cosine wave.
FIG. 1
a
shows a conventional poly-phase quadrature signal generator of the most simple structure. The poly-phase quadrature signal generator includes two resistors
104
and
107
, and two capacitors
105
and
106
. If differential input signals v
in
(0°), v
in
(180°) are inputted through input terminals
100
and
101
, differential output signals v
out
(90°), v
out
(270°) are produced through the output terminals
102
and
103
. At this time, assuming that R
1
=R
2
=R and C
1
=C
2
=C, the transfer function between the input and the output is expressed as follows: V
out
*/V
in
*=(1−sRC)/(1+sRC). As a result, phase shifts by −2 tan
−1
&ohgr;RC. V
in
* and V
out
* represent the differential input signals v
in
(0°), v
in
(180°) and v
out
(90°), v
out
(270°), respectively. s indicates j&ohgr; and &ohgr; indicates an angular frequency. Therefore, when &ohgr;=1/RC, the output is the differential quadrature signal (poly-phase quadrature signal) having same amplitude and phase difference of 90° compared with the input. In a typical integrated circuit manufacturing process, however, there exist errors in the amplitude and phase as the range in an error of the resistor and the capacitor is high. In order to correct the errors between the quadrature signals, therefore, it is required that a variable resistor or a variable capacitor be used.
Hereinafter, signals having relative phases of 0° and 180° are called I-signal (in-phase signal) and signals having relative phases of 90° and 270° are called a Q-signal (quadrature-phase signal), according to common high frequency communication terminology.
FIG. 1
b
illustrates a conventional poly-phase quadrature filter. Resistors
118
~
121
and capacitors
126
~
129
form a first order filter network. Also, resistors
122
~
125
and capacitors
130
~
133
form a second order filter network. However, a high order filter network can be designed depending on its purposes. If the values of the resistors forming respective filter networks are same and are called R, and the values of the capacitors are same and are called C, the transfer function of the output signal to the differential input signal v
in
(0°), v
in
(180°) when the differential input signal v
out
(90°), v
out
(270°) is grounded can be expressed as Equation 1.
V
I
—
out
*/V
in
*=2
sRC
/{(
sRC
)
2
+4
sRC+
1},
V
Q
—
out
*/V
in
*={1−(
sRC
)
2
}/{(
sRC
)
2
+4
sRC+
1}  [Equation 1]
where, V
I
—
out
* is the differential output signal, v
out
(0°), v
out
(180°), in other words, the I-signal. Also, V
Q
—
out
* is the differential output signals, v
out
(90°) and v
out
(270°), in other words, the Q-signal. As the poly-phase quadrature filter is basically a passive circuit network, attenuation of the signal becomes great as the order of the circuit network is increased. The errors of the amplitude and the phase of the differential quadrature signal are also significantly increased by errors in the manufacturing process of the resistors and the capacitors. As shown in Equation 1, the I-signal represents a low-pass characteristic and the Q-signal represents a high-pass characteristic. Thus, as the frequency characteristics of the two differential quadrature signals are different, there exists difference in the modulation of the I-signal and the Q-signal by the low-frequency coupling or the high-frequency coupling due to the leakage, which causes errors in the amplitude and the phase. In order to generate exact differential quadrature signal in a desired frequency range, therefore, there is a need for a quadrature signal generator having a bandpass characteristic through which corresponding frequency components are passed but unnecessary signal by the leakage are rejected.
FIG. 1
c
shows a modified version of the poly-phase quadrature signal generator in
FIG. 1
a
. Transistors
141
~
144
which are bipolar junction transistors(BJT) operate as an input buffer. A P type MOSFET Qc
1
and Qc
2
which are driven in a linear region, and resistors R
1
and R
2
, are connected in parallel to form variable resistors
134
and
135
. Thus, the gate voltage of the P type MOSFET is varied to control the effective resistor value, so that errors in the amplitude and the phase between two differential quadrature signals(I-signal and Q-signal) can be controlled. At this time, necessary control voltage is supplied from the outside through a node
136
. As this type of the structure basically includes the resistors and the capacitors, the pole frequency is increased as the frequency is increased. Therefore, desired values of the resistors and capacitors become small. Consequently, there are problems that the structure could not be reliably implemented and implementation at the high frequency band is limited.
SUMMARY OF THE INVENTION
The present invention is contrived to solve the above problems and an object of the present invention is to provide a quadrature signal generator by which amplified quadrature signals are produced using a load having a low-pass filter characteristic using resistors and capacitors and a load having a high-pass filter characteristic using the resistors and inductors in a signal amplifier structure and variation in the phase representing respective loads, and quadrature signals are produced by implementing it as the differential structure, thus controlling amplitude errors and phase errors using a variable resistor and a variable condenser and removing signal errors(amplitude errors, phase errors) by coupling the bandpass resonators.
Another object of the present invention is to provide a quadrature signal generator that can be used in microwave and millimeter-wave regions as well as the radio frequency(RF) region, using an inductor other than an existing resistors-the capacitor structure.
In order to accomplish the above object, a quadrature signal generator according to the present invention, comprising a means for generating two-phase quadrature signals using a low-pass filter having resistors and a capacitors and a high-pass filter having resistors and a inductors, and a differential amplifier for generating amplified poly-phase quadrature signals, wherein the low-pass filter and the high-pass filter are connected to respective loads.
The values of the resistors and the capacitor in the low-pass filter are varied depending on the amplitude and phase of signal

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