Pulse or digital communications – Transceivers
Reexamination Certificate
2000-09-29
2004-02-17
Bocure, Tesfaldet (Department: 2631)
Pulse or digital communications
Transceivers
C375S297000
Reexamination Certificate
active
06693956
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a power amplifier having a negative feedback circuit for a transmitter and more particularly to a negative feedback circuit for compensating for a nonlinear distortion used in the transmitter and a method for controlling the phase of the circuit in the power amplifier.
A radio system arranged to use a linear digital modulation system such as 16QAM (Quadrature Amplitude Modulation) or &pgr;/4 shift QPSK (Quadrature Phase Shift Keying) essentially needs nonlinear distortion compensation for a power amplifier. In actual, the radio system utilizes various kinds of nonlinear distortion compensating systems (linearizers). Of those systems, a Cartesian loop negative feedback type linearizer has been conventionally used. The conventional linear feedback amplifier will be described with reference to FIG.
2
.
FIG. 2
is a block diagram showing an arrangement of a transmitting section of a digital radio transmitter provided with the Cartesian loop negative feedback type linenarizer.
A numeral
1
denotes a baseband signal generator, which operates to output an in-phase component (called an I-component) and a quadrature component (called a Q-component) of a baseband signal. The I-component is added to the feedback signal in an adder
2
-
1
and then the added signal is outputted and is applied into a loop filter
3
-
1
. Likewise, the Q-component is added to the feedback signal in the adder
2
-
2
and then the added signal is applied into a loop filter
3
-
2
. The loop filters
3
-
1
and
3
-
2
operate to restrict the bandwidths of the I-component and the Q-component and then apply the resulting components into a quadrature modulator
4
.
A numeral
11
denotes a reference signal generator, which operates to generate a reference frequency signal and then apply the reference signal into PLL frequency synthesizers
12
and
13
. The PLL frequency synthesizer
12
operates to generate a first local oscillating signal (called an LO signal) on the basis of the reference signal and then apply a first LO signal into a quadrature modulator
4
and a phase shifter
18
. The PLL frequency synthesizer
13
operates to generate a second LO signal on the basis of the reference signal and then apply the second LO signal into mixers
6
and
15
. The phase shifter
18
operates to control the phase of the first LO signal through the use of a control signal to be applied from a phase controller
19
and then apply the first LO signal whose phase is controlled into the quadrature demodulator
16
.
The quadrature modulator
4
operates to orthogonally modulate the first LO signal (carrier) into a signal of an intermediate frequency band (called an IF frequency band) by the I-component I′ and the Q-component Q′ of the baseband signal to be applied therein. Then, the modulated signal is applied into a bandpass filter (BPF)
5
. The bandpass filter
5
operates to remove unnecessary components from the modified signal and then apply the resulting signal into the mixer
6
. The mixer
6
operates to convert the signal applied therein into a desired frequency through the use of the second LO signal outputted from the PLL frequency synthesizer
13
and then apply the converted signal into a bandpass filter (BPF)
7
. The bandpass filter
7
operates to remove unnecessary spurious components from the applied signal and then send the resulting signal into the power amplifier (PA)
8
. The power amplifier
8
operates to amplify the input signal up to a specified output level and then transmit the amplified signal through an antenna
9
.
This negative feedback amplifier is arranged as a negative feedback linearizer based on the Cartesian loop. Hence, part of the output signal of the power amplifier
8
is fed back through a directivity coupler
10
and then is given to an attenuator (ATT)
14
. The attenuator
14
operates to adjust the power level of the input signal into a proper value and then give it to the mixer
15
. The mixer
15
operates to convert the signal applied from the attenuator
14
into the IF frequency through the use of the second LO signal and then apply the converted signal into the quadrature demodulator
16
.
The quadrature demodulator
16
operates to produce respectively the baseband signals i and q of the I- and the Q-components by orthogonally demodulate the converted signal using the first LO signal applied from the phase shifter
18
. The I-component is applied as the I-component i of the feedback signal into a subtracting input side of the adder
2
-
1
through a switch
20
-
1
, while the Q-component is applied as the Q-component q of the feedback signal into the subtracting input side of the adder
2
-
2
through a switch
20
-
2
. At this time, the output sides of the switches
20
-
1
and
20
-
2
are connected to the adders
2
-
1
and
2
-
2
, respectively.
In this type of negative feedback, for stabilizing the system, it is necessary to keep the input signals I and Q the same as the feedback signals i and q in phase (no phase difference) on the input sides of the adders
2
-
1
and
2
-
2
. That is, if the phase difference takes place between the input signal and the feedback signal, it is necessary to make the phase difference zero by controlling the phase to be shifted by a radian at the maximum.
In turn, the method for controlling the phase will be described below. At first, the switches
20
-
1
and
20
-
2
shown in
FIG. 2
are switched to be connected to the phase controller
19
so that the feedback loop is held in an open state.
The baseband signal generator
1
operates to apply a predetermined DC voltage into only the I-component for the purpose of adjusting the phase. The Q-component is kept zero (Q=0). In this state, the quadrature modulation is proceeded along the foregoing operation and then the signal is sent out through the antenna
9
. Then the output waveform of the power amplifier
8
takes a non-modulated carrier. The output of the power amplifier
8
is partially fed back by the directivity coupler
10
. Consider the output of the feedback signal of the quadrature demodulator
16
along the foregoing operation. If the phases coincide with each other, the DC voltage appears only on the I-component side, while no signal (DC) appears only on the Q-component side. However, if the phases do not coincide with each other, the DC voltage corresponding to the phase shift appears on the output of the Q-component side. Hence, the angle of rotation of the phase can be derived from the DC voltages of the I and the Q-components.
In the phase controller
19
, the phase corresponding to the derived angle of rotation is reversely controlled by controlling the phase shifter
18
so that the phase of the first LO signal may be adjusted. By coinciding the output of the feedback signal of the quadrature demodulator
16
with the input signal, the negative feedback may be stabilized. Since the phase fit of the input signal and the feedback signal makes the output on the Q-component side zero, then the switches
20
-
1
and
20
-
2
are changed to the adders
2
-
1
and
2
-
2
, respectively, so that the loop is made closed.
In the foregoing prior art, each time the phase is adjusted, it is necessary to open and close the feedback loop. It means that the loop is open while the phase is being adjusted. Hence, the phase adjustment cannot be executed for the change of phase while the transmission is in operation (closed loop). Further, the switching means for opening and closing the loop is located so that the phase may be controlled by the DC voltage of the feedback signal on the input side of the switching means. Hence, the voltage drop in the switching means in the open loop is different from that in the closed loop, so that the compensation of the offset voltage of the system set in the closed loop is not adaptive to the open loop. It means that the precise phase control cannot be executed. Further, if the phase is changed by changing the phase characteristic because of the temperature varia
Antonelli Terry Stout & Kraus LLP
Bocure Tesfaldet
Hitachi Denshi Kabushiki Kaisha
LandOfFree
Power amplifier having negative feedback circuit for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power amplifier having negative feedback circuit for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power amplifier having negative feedback circuit for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3305034