Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2000-06-30
2002-07-02
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
Reexamination Certificate
active
06414548
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a differential amplifier having two channels, each channel having an input, an output and a transistor.
Differential amplifiers of this type are disclosed, for example, in the textbook “Halbleiter-Schaltungstechnik” [“Semiconductor Circuit Technology”], pages 361 ff, Tietze/Schenk, 11th Edition, Springer Publishers. These conventional differential amplifiers are symmetrical amplifiers having two inputs and two outputs. The differential amplifier is formed of two common emitter circuits or two common source circuits, if field-effect transistors are being used, and the differential amplifier is used to amplify a differential voltage between the two inputs. The differential amplifier is generally operated using a positive and a negative supply voltage, which are preferably in symmetrical form. If only one positive or only one negative supply voltage is available, ground may be used as the second supply voltage.
Such differential amplifiers are frequently used as voltage-controlled current sources. Important criteria for these differential amplifiers are high linearity, that is to say a constant conversion factor between the input voltages and the output voltages or output currents, a high bandwidth and low noise. If high linearity is achieved only at the expense of a high voltage requirement and a low transmission factor, this may have disadvantageous effects, particularly with low operating voltages, such as in mobile radio appliances, which are operated using rechargeable batteries.
In order to linearize differential amplifiers, emitter resistors may be used for example, but these impair the noise properties and a high level of negative feedback is required for high linearity, so that the necessary input voltage becomes correspondingly higher and higher. This is particularly disadvantageous if the operating voltage available is low. An operational amplifier is therefore frequently also used in order to linearize the amplifier. However, this results in additional costs and offset voltages. Also, a pnp-npn Darlington transistor may be used, but this is unfavorable in the manufacturing process for large-scale production, since pnp transistors have, in standard processes, disadvantageous properties with regard to bandwidth, current-gain etc. Modern manufacturing processes allow high-quality pnp transistors to be produced, albeit at the expense of additional process steps in the manufacturing process, and hence at the expense of additional manufacturing costs.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a differential amplifier which overcomes the above-mentioned disadvantages of the heretofore-known amplifiers of this general type and which requires only low operating voltages, is additionally inexpensive to manufacture and which presents no problems with regard to mass production as an integrated circuit.
With the foregoing and other objects in view there is provided, in accordance with the invention, a differential is amplifier, including:
a first channel and a second channel;
each of the first and second channels having an input, an output and a terminal to be connected to a supply voltage, a transistor with a first controlled path, a first current source connected to the first controlled path, the first controlled path being connected to the terminal via the first current source, a second current source having a second controlled path connected in series with the first controlled path, the second current source being a voltage controlled current source, a third current source connected to the output, the third current source being a controlled current source, a potential-shifting device connected to the first current source, the second and third current sources being controllable via the potential-shifting device; and
a resistor connected to the first controlled path in the first channel and to the first controlled path in the second channel for connecting the first channel to the second channel.
In other words, the inventor proposes to modify the conventional type of differential amplifier including two channels, each having an input, an output, an emitter transistor and a first current source, the channels being connected to one another via a resistor, by assigning a potential-shifting device or level shifter to the current source in at least one channel, and by providing a voltage-controlled, second current source for linearization purposes, the output of the differential amplifier being formed by a further, third controlled current source. The further, third current source can then supply a current which is proportional to the current from the second current source, and, in this way, ensures that the linearity of the differential amplifier according to the invention is significantly improved in the context of the circuit configuration.
The differential amplifier may preferably be configured such that at least one of the two first current sources is in the form of a constant current source.
In addition, it is particularly advantageous if the two channels of the differential amplifier are of a symmetrical configuration.
Advantageously, a diode or a transistor connected as a diode may also be used as the potential-shifting device. The result of this is that the circuit is kept simple and retains a high bandwidth.
In accordance with another feature of the invention, the potential-shifting device is formed by a resistor, a voltage source or a Z-diode instead of the transistor or the diode.
In accordance with yet another feature of the invention, at least one of the two voltage-controlled, second current sources is formed of a transistor.
In accordance with a further feature of the invention, at least one linearization device may also be in the form of a transistor or a voltage-controlled current source, for example the second current source.
In accordance with yet a further feature of the invention, the at least one transistor of the linearization device and the at least one transistor of the current source in at least one respective channel are connected by their respective bases.
With regard to mass production, it is particularly advantageous if at least one transistor of the differential amplifier, but preferably all the transistors of the differential amplifier, is/are in the form of (an) npn transistor(s). In this way, high frequencies can also be processed using the circuit.
Alternatively, it is also possible for the transistor or transistors of the differential amplifier to be in the form of pnp transistors, however disadvantages with regard to mass production and amplifier properties have to be accepted.
Another possibility for the configuration of the circuit configuration according to the invention is for at least one transistor of the differential amplifier, preferably all the transistors of the differential amplifier, to be (an) FET transistor(s).
The controlled path of an npn or pnp transistor is its collector/emitter path. The control connection of the bipolar transistor is its base electrode. The controlled path of a MOS field-effect transistor is its drain/source path. The control connection of the MOS field-effect transistor is its gate electrode.
It is noted that the features of the invention which are mentioned above and are yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or alone, without departing from the scope of the invention.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a differential amplifier, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with addi
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Mottola Steven J.
Stemer Werner H.
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