Pulse or digital communications – Testing
Reexamination Certificate
2000-06-29
2003-05-27
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Testing
C375S296000, C375S298000, C375S345000, C370S252000, C324S076130
Reexamination Certificate
active
06570914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an amplitude calculation circuit. More particularly, the invention relates to an amplitude calculation circuit for accurately calculating an amplitude in a base band (I signal and Q signal) of a communication device employing a quadrature phase modulation.
2. Description of the Related Art
In the conventional amplitude calculation circuit, an amplitude of a base band [I (In-phase) signal and Q (Quadrature-phase) signal] of a communication device employing an quadrature phase modulation is accurately calculated. In this circuit, from the I, Q base band signals, an amplitude expressed by:
A
(
t
)=|
G
(
t
)|={square root over ( )}[
I
(
t
)
2
+Q
(
t
)
2
] (1)
can be accurately derived.
wherein A(t) is an amplitude of an quadrature modulation wave, t is a time, G(t) is an quadrature modulation wave, I is an amplitude of a component (in-phase component) in-phase relationship with a carrier, and Q is an amplitude of a component (quadrature phase component) in an quadrature phase relationship with the carrier. The foregoing technology will be an important technology toward future in an quadrature phase modulation type communication system.
For example, it becomes necessary to derive an amplitude from received I and Q signals, to compare with a predetermined value, and to perform AGC (Automatic Gain Control). Conventionally, there is no method for deriving the amplitude from the I and Q signals simply and in high precision. In this circumstance, currently, an approximated value expressed by:
A
′=max (|
I|,|Q
|)+½·min(|
I|,|Q
|) (2)
has been used. This contains significant error in comparison with the correct amplitude.
On the other hand, if a instantaneous amplitude can be accurately calculated from the base band signal at a transmission side, it becomes possible to perform control for increasing a bias current of a transmission power amplifier when the amplitude is large and for decreasing the bias current of the transmission power amplifier, using the result of calculation of the instantaneous amplitude. By performing such control, a distortion at a peak of the amplitude can be reduced with maintaining an average consumption of current.
Furthermore, currently, in order to achieving improvement of efficiency of a transmission amplifier, a predistorter which is a kind of linearizer is considered as promising. In the predistorter, accurate amplitude calculation is inherently required. An example of this is shown in FIG.
11
.
In
FIG. 11
, an input signal Sr is consisted of a base band signal Ir of an in-phase component with a transmission carrier and a base band signal Qr of quadrangular-phase component of the transmission carrier. The input signal can be considered as a complex number taking the signal Ir as a real number portion and the signal Qr as an imaginary number portion.
The input signal Sr, namely the signal Ir as the real number portion and the signal Qr as the imaginary number portion operated by complex multiplication with a distortion correction data (real number portion is Re and imaginary number portion Im) from a ROM (read-only-memory) by a complex multiplier
20
. The complex multiplier
20
comprises multipliers
1
to
4
and adder and subtracter
5
and
6
.
The output of the complex multiplier
20
is a complex signal Sp, in which amplitude and phase of the input signal Sr are corrected so that a characteristics of a non-linear amplifier
11
becomes linear. As a result of complex multiplication, the complex signal Sp is expressed by:
Sp=Sr·a·exp
(
j
&thgr;) (3)
wherein a is an amplitude correction value and &thgr; is a phase correction value.
Accordingly, correction data are expressed by:
Re=a
·cos(&thgr;)
Im=a
·sin(&thgr;) (4)
The complex signal Sp is a signal derived by multiplying the amplitude of the input signal Sr by a and phase thereof is rotated for &thgr; and can be calculated by using the real number portion Re and the imaginary number portion Im.
Assuming the real number portion of the complex signal Sp is Ip and the imaginary number portion is Qp, Ip and Qp are expressed by:
Ip=Re·Ir−Im·Qr
Qp=Re·Qr+Im·Ir
(5)
The signals of the real number portion Ip and the imaginary number portion Qp are converted into analog signals by D/A (digital-to-analog) converters (DACs)
7
and
8
and then are converted into high frequency signals by a quadrature modulator
9
.
On the other hand, an amplitude calculation circuit
15
calculates and outputs an instantaneous amplitude |Sr| of the input signal Sr. The instantaneous amplitude |Sr| is expressed by:
|
Sr|={square root over ( )}[Ir
2
+Qr
2
] (6)
This equation (6) is the same as the equation (1).
On the other hand, the output of the non-linear amplifier
11
is branched by a coupler
12
and is rectified by a rectifier
19
. Then, an average transmission amplitude is derived by a low-pass filter (LPF)
18
. This signal converts into a digital signal by an A/D (analog-to-digital) converter (ADC)
17
to derive an average transmission amplitude.
The instantaneous amplitude |Sr| and the average transmission amplitude of the input signal Sr are multiplied by a multiplier
30
. The result (product) of multiplication represents an instantaneous amplitude. This value is used as an address input for a distortion compensation ROM (look-up table) 14.
In the conventional amplitude calculation circuit set forth above, it is required to calculate quite accurately. In order to realize this, a method to read out the amplitude from ROM table with taking the I and Q signals as addresses.
This method has been disclosed in “Quantization Analysis and Design of a Digital Predistortion Linearizer for RF Power Amplifiers” (Sundstrom. L.; Faulkner, M.; Johansson, M., Vehicular Technology, IEEE Trans., Vol. 45 4, page 707-719).
However, in such method, ROM having quite large capacity becomes necessary for deriving accurate amplitude. This has been the most important problem. As set forth above, it has been important task for calculating accurate amplitude from the I, Q base band signals irrespective of transmission side or reception side in the quadrature phase modulation type communication device.
SUMMARY OF THE INVENTION
The present invention has been worked out in view of the problems set forth above. Therefore, it is an object of the present invention to provide an amplitude calculation circuit which can calculate an accurate amplitude with quite small circuit scale and quite small power consumption.
According to the first aspect of the present invention, an amplitude calculation circuit comprises:
a plurality of circuits, each including
an absolute value calculating circuit receiving a pair of base band signals and calculating respective absolute values thereof; and
a phase rotation circuit receiving the absolute values as components of two-dimensional vector and rotating the two-dimensional vector over a predetermined rotational angle for outputting as component of the vector;
the plurality of circuits being connected in cascade connection for receiving respective of the base band signals as input signal at a first stage and outputting an output of the phase rotation circuit of a final stage as a result of amplitude calculation.
Namely, the amplitude calculation circuit of the present invention relates to the circuit for calculating the amplitude of a high frequency signal from a values of I and Q base band signals in a radio transmitter device generating a high frequency signal through an quadrature phase modulation of I and Q base band signals or in a radio receiver device reproducing the I and Q base band signals by quadrature demodulation of a received high frequency signal.
The amplitude calculation circuit
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