JPH0691389B2 - Gain control amplifier - Google Patents

Description

The present invention relates to a gain control amplifier having a variable current source.

[Outline of Invention]

The present invention relates to a gain control amplifier having a variable current source, in which a plurality of differential amplifiers having different operating points are connected in parallel so that the gain changes linearly with respect to a control voltage. Is.

[Conventional technology]

A conventional gain control amplifier is constructed as shown in FIG. 4, for example.

In FIG. 4, (10) and (20) are differential amplifiers, in which the signal input terminal (1) is connected to the base of one transistor (11) of the first stage differential amplifier (10) and the other transistor is connected. A bias power supply E ₁ for setting the operating point is connected to the base of (12). Resistors (13) and (14) are connected to the emitters of both transistors (11) and (12), and a power supply V is connected to each collector via diodes (15) and (16).
_cc is supplied. The collectors of both transistors (11) and (12) are connected to the bases of transistors (21) and (22) of the next-stage amplifier (20), respectively, and the emitters of both transistors (21) and (22) have a common constant. It is grounded via a current source (23). The collector of one transistor (21) is directly connected to the power supply V _cc and the other transistor (2
The collector of 2) is connected to the power supply V _cc via the load resistor (24) and is also connected to the output terminal (2).

Reference numeral (30) is a differential amplifier as a variable current source, in which the control input terminal (3) is connected to the base of one transistor (31) and the bias power supply E ₃ is connected to the base of the other transistor (32). Connected. Transistors (31) and (3
Each emitter in 2) is connected to a common constant current source (35) via resistors (33) and (34). The collector of one transistor (31) is directly connected to the power supply V _cc, and the collector of the other transistor (32) is at the connection midpoint P of both emitter resistors (13) and (14) of the first stage amplifier (10). Connected. Further, the connection midpoint P is grounded via the constant current source (4).

The operating currents of the first-stage and second-stage differential amplifiers (10) and (20) are I ₁ and I ₂ , respectively, and the resistance values of both emitter resistors (13) and (14) are both R _e1 and the load resistor. When the resistance value of (24) is R _l , the gain G from the signal input terminal (1) to the output terminal (2) is expressed by the following expression (1).

[Problems to be Solved by the Invention] By the way, as is apparent from FIG.
The operating current I ₁ of 0) is the current I ₀ of the constant current source (4) and the collector current of the other transistor (32) of the variable current source (30).
It is the sum of I ₃₂ . Then, the collector current I ₃₂ in response to the control voltage E _c supplied from the voltage and the terminal of the bias power supply E ₃ (3), shall apply those current I ₃ of the constant current source (35) is diverted And changes linearly from the maximum value I ₃ to the minimum value 0. Therefore, the operating current I ₁ of the first stage amplifier (10) is
As shown in FIG. 5, as the control voltage E _c increases, it changes linearly from the maximum value I ₀ + I ₃ to the minimum value I ₀ .

However, as shown in the above equation (1), since the gain G of the gain control amplifier of FIG. 4 is inversely proportional to the operating current I ₁ of the first stage amplifier (10), the gain characteristic with respect to the control voltage V _c is the sixth. It becomes a hyperbola as shown in the figure, and the slope of the characteristic curve becomes steep in the high gain portion. This means that the control sensitivity is high in the high gain portion, and therefore, the gain control amplifier of FIG. 4 has a problem that the control becomes difficult at the high gain.

In addition, such a gain control amplifier has a comparator and a D-
When used with an A converter or the like, there was a problem that the bit error becomes large at high gain.

In view of this point, an object of the present invention is to provide a gain control amplifier whose gain changes linearly with respect to a control voltage.

[Means for solving problems]

The present invention provides a gain control amplifier having a variable current source, a variable current source, each of the operating points _{E 3, E 4, E 5} ... plurality of differential amplifiers having different _{E n (30), (40} ), (50) ... A gain control amplifier configured by connecting N in parallel.

[Action]

According to the present invention, the gain of the amplifier is linearly controlled with respect to the control voltage.

[Embodiment] An embodiment of the gain control amplifier according to the present invention will be described below with reference to FIGS. 1 to 3.

The configuration of one embodiment of the present invention is shown in FIG. In FIG. 1, parts corresponding to those in FIG. 4 are designated by the same reference numerals, and redundant description will be omitted.

In FIG. 1, reference numerals (40), (50), ... N denote differential amplifiers, which have the same structure as the differential amplifier (30).
The control voltage E _c from the terminal (3) is applied to each differential amplifier (30),
(40), (50) ... One of the N transistors (31),
(41), (51) ... N1 are commonly supplied to the bases of the other transistors, and the other transistors (32), (42), (52) ... N2.
Bias power supply E ₃ , E ₄ , E ₅ … E _N
Are connected. The collectors of the transistors (31) to N1 on one side are directly connected to the power source V _cc, and the collectors of the transistors (32) to N2 on the other side are connected to the emitter resistors (13) and (14) of the first stage amplifier (10). ) Connected midpoint P. Each differential amplifier (40), (50) ... N pair of emitter resistors (43), (44); (53), (54); ... (N3),
(N4) are connected to common constant current sources (45), (55) ... N5, respectively. The remaining structure is the same as that of the conventional example shown in FIG.

In the present embodiment, the resistance values R _e3 , R _e4 , R _e5 ...... R of the respective pairs of emitter resistors of the differential amplifiers (30), (40), (50), ... _en , current value of each constant current source I ₃ , I
The _4, I ₅ ... I _N and the voltage value E ₃ of the bias power _{supply, E 4, E 5 ... E} N,
For example _{I 3 R e3 <I 4 R} e4 <I 5 R e5 <... <I N R en ... (2) E 3 <E 4 <E 5 <... <E N ... (3) appropriately set to as As a result, the control characteristic of the operating current I ₁ of the first-stage amplifier (10) with respect to the control voltage E _c becomes hyperbolic polygonal lines l _{3 to} l _n , as shown in FIG.

As described above, from the signal input terminal (1) to the output terminal (2)
Since the gain G up to is inversely proportional to the operating current I ₁ of the means amplifier (10), the control characteristic of the gain with respect to the control voltage E _c in this embodiment becomes linear as shown in FIG. Regardless of the level, the control sensitivity is constant.

〔The invention's effect〕

As described above in detail, according to the present invention, a plurality of differential amplifiers having different operating points are connected in parallel to form a variable current source having a hyperbolic current control characteristic. A linear gain control amplifier can be obtained.

[Brief description of drawings]

FIG. 1 is a connection diagram showing the configuration of an embodiment of a gain control amplifier according to the present invention, FIGS. 2 and 3 are diagrams for explaining the operation of an embodiment of the present invention, and FIG. FIG. 5 is a connection diagram showing a configuration example of the gain control amplifier of FIG. 5, and FIGS. 5 and 6 are diagrams for explaining the operation of the conventional example. (30), (40), (50) ...... N differential amplifier as a variable current _{source, E 3, E 4, E} 5 ... E N denotes a bias power source.

Claims (1)

[Claims] 1. An amplifying means in which a gain changes hyperbolically in inverse proportion to a linear change of an operating current, and a variable current source for supplying an operating current according to a supplied control voltage to the amplifying means. A gain control amplifier capable of controlling the gain of the amplifying means by a control voltage supplied to the variable current source, wherein a plurality of differential amplifiers having different operating voltage points with respect to the control voltage are used as the variable current source. Are connected in parallel to the amplifying means, and the respective operating voltage points are set so that the change of the gain of the amplifying means with respect to the control voltage becomes substantially linear. .