Amplifiers – Hum or noise or distortion bucking introduced into signal...
Patent
1997-01-28
1998-12-08
Mullins, James B.
Amplifiers
Hum or noise or distortion bucking introduced into signal...
330 85, 330110, H03F 132
Patent
active
058476040
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase of international application PCT/FI96/00151, filed Mar. 12, 1996 which designates the U.S.
BACKGROUND OF THE INVENTION
The invention relates to a linearizer comprising an amplifier and a compensating non-linearity located in its feedback path. A linear control voltage applied to the input of the amplifier is transformed in the linearizer such that the non-linearity of the non-linear element controlled by the transformed control voltage is essentially compensated, such that the output voltage of the non-linear element is essentially linearly dependent on the linear control voltage.
In radio unit transmitters, voltage-controlled components, such as RF attenuators and amplifiers, are used. The attenuation/amplification of these components in the adjustment range should be linearly dependent on the adjustment voltage. A typical embodiment is a power levelling loop in which the input power of an RF signal supplied to an amplifier of a transmitter is essentially a constant, and the power of a signal output from the amplifier must be adjusted over a wide range at submicrosecond speed. The characteristic of most voltage-controlled components is non-linear, i.e. without any specific linearization the attenuation G of the amplifier, i.e. the ratio of output voltage V.sub.out to input voltage V.sub.in as a function of control voltage V.sub.c, is as illustrated by the graph of FIG. 1 of the attached drawings. As the control voltage increases from zero, the graph first shows a leakage region 1, where attenuation G has a minimum value. It is almost independent of control voltage V.sub.c. As the control voltage increases, a first linear transition region 2 follows. In this region, attenuation is a linear function of the control voltage. The next region is an exponential or dB-linear region 3, where attenuation is an exponential function of the control voltage. With a further increase in the control voltage, a second linear transition region 4 follows. Here, too, attenuation is a linear function of the control voltage. The last region is a saturation region, where attenuation has a maximum value which is almost independent of the control voltage.
In most embodiments, a required property of voltage-controlled components is linearity. As previously known, this can be achieved by the use of a specific linearizer. The objective of the linearizer is to transform the linear control voltage supplied thereto to non-linear control voltage whose characteristic is inverse to the characteristic of the voltage-controlled component, whereby they combine to form a linear characteristic of a voltage-controlled component.
FIG. 2 shows the principle of a typical inverting linearizer known in the field. A non-linear circuit 22 is placed in the feedback path of a high-gain non-linear operation amplifier 21. The input of the amplifier is the voltage V.sub.LIN to be linearized, and from the output is obtained non-linear control voltage V.sub.c, which is supplied to a voltage-controlled attenuator/amplifier 23, where it compensates for non-linearity G.
In order that non-linearity G could be compensated, it should be either a monotonically ascending or monotonically descending function of control voltage V.sub.c, whereby it can be represented by formula (1): .+-.g.sub.01 (V.sub.0) (1) function. V.sub.01 is an offset term and A is a scaling factor, which are used for expressing non-linearity G as a function of voltage V.sub.0. The non-linear circuit 22, which can be called a compensating non-linearity, produces a feedback current I.sub.0 =I.sub.00 .+-.I.sub.01 (V.sub.0), where I.sub.00 is a constant part and I.sub.01 is a part dependent on voltage V.sub.0. Voltage V.sub.0 is obtained from output voltage V.sub.c by scaling by A and offsetting by V.sub.01. The scaling and offsetting can be performed using resistor networks. The plus sign is used when the amplifier is a non-inverting amplifier, and the minus sign when it is an inverting one. Non-linearity I.sub.01 is called the compensating non-linearity, wh
REFERENCES:
patent: 3686555 (1972-08-01), Younkin
patent: 4549146 (1985-10-01), Cowans et al.
patent: 4774476 (1988-09-01), Ecklund et al.
patent: 4816722 (1989-03-01), Klotz
Mullins James B.
Nokia Telecommunications Oy
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