JPS5995708A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To obtain selectively a positive and a negative output with a few lead terminals by switching one of different polarities of the 1st and the 2nd differential amplifiers selectively by means of an output of a voltage comparator and leading the result to an output terminal. CONSTITUTION:When a voltage of a reference voltage source 9 is 5V and a voltage at a terminal 3 is 0-5V, a switch 10 connects a positive output of a differential amplifier 2 to a terminal 4 by an output of a voltage comparator 8. When a voltage at the terminal 3 is 5-10V, the output of the comparator 8 is inverted and a negative output of the differential amplifier 6 is outputted to the terminal 4 via the switch 10. Since a voltage of 5-10V is applied to the terminal 3, the voltage is corrected into the original range (0-5V) by a level shift circuit 7 and the result is impressed to the amplifier 6. Thus, the polarity is switched selectively by a voltage at the terminal 3, and the ratio of performance to cost of an IC is improved.

Description

[Detailed description of the invention] The present invention relates to an amplifier circuit capable of switching output polarity.

Conventionally, differential amplifiers have been widely used in integrated circuit devices (hereinafter referred to as ICs). In order to unnecessarily increase the number of terminals and worsen the price/performance ratio, only the normally necessary terminals are brought out of the IC.

SUMMARY OF THE INVENTION An object of the present invention is to provide an amplifier circuit that can selectively draw out positive and negative polarity outputs of a differential amplifier with a smaller number of lead-out terminals.

The amplifier circuit of the present invention has first and second differential amplifiers, at least one level shift circuit, a voltage comparator circuit, and input and output terminals, A first polarity input terminal of each amplifier and a second polarity input terminal of each amplifier are formed as a pair, at least one of which is connected via the level shift circuit, and the other pair is connected to the input terminal, An input terminal of the input terminal is applied to the voltage comparator circuit, and an output of the voltage comparator selectively switches the negative polarity of the first and twentieth differential amplifiers and outputs the negative polarity to the output terminal. It is characterized by what it did.

Next, a detailed explanation will be given with reference to the drawings. FIG. 1 shows an example of an IC including a conventional differential amplifier, in which 1 is an integrated circuit device;
In the 2-digit differential amplifier, 3 is a negative input terminal used as a reference voltage input, 41 is a positive output terminal, and 42 is a negative output terminal. Further, the positive polarity input of the differential amplifier 2 is connected to other circuits (not shown) within the ICI. Such examples are widely used in ICs including negative feedback amplifiers and voltage comparators.

FIG. 2 is a block diagram showing an embodiment of the present invention. 1st
Components that are the same as those in the figure are given the same reference numerals. This amplifier circuit has a differential amplifier 6 in addition to the conventional differential amplifier 2, and uses the former for positive polarity output and the latter for negative polarity output, and connects the output terminal 4 to the desired output via an electronic switch 10. The polarity of the output is obtained. Here, the voltage at the input terminal 3 is used as the polarity switching signal. To be more specific, for example, if the voltage of the reference voltage source 9 is 5V, when the voltage of the terminal 3 is 0 to 5V, the output of the voltage comparator 8 causes the electronic switch 10 to connect to the positive terminal of the differential amplifier 2. The output is connected to terminal 4. Further, when the voltage at the terminal 3 is 5 to IOV, the output of the voltage comparator 8 is inverted, and the negative polarity output of the differential amplifier 6 is outputted to the terminal 4 via the electronic switch 10. At this time, since the voltage of 95 to 10V is applied to the terminal 3 as mentioned above, the level shift circuit 7 transfers it to the original range (
0 to sV) and applied to the differential amplifier 6. In this way, the polarity can be selectively switched by the voltage of the terminal 3, and there is no need for a terminal corresponding to the terminal 5 in FIG. 1, so 1. The performance M curvature ratio can be improved in C.

Furthermore, the level shift circuit 7 does not necessarily have to be placed in the position shown in FIG. p5V is higher than that of dynamic amplifier 2. Until now, differential amplifiers 2 and 6 were used more than other circuits in the IC.
It was assumed that the voltage applied to the positive input of the circuit was approximately within the range of 0 to 5V, but if this is not the case, level shifting may be performed as necessary.

FIG. 3 is a circuit diagram specifically showing the embodiment of FIG. 2.

Q1 to Q9 represent transistors, and R1 to R6 represent resistors. A signal from another circuit (not shown) in the IC (its variation range is within 2 to 6 V) is applied to the pace of Q6, and the signal as shown in FIG. The pace of Q5 corresponds to the positive polarity input of the differential amplifier 2 in FIG.
It is applied to the pace of 3. On the other hand, the terminal 3 is connected to the differential amplifier 2 of FIG.
is connected to the pace of Q4, which corresponds to the negative polarity input of It is connected to the pace of Q2, which corresponds to the negative input of the differential amplifier 6 in the figure, and is further connected to the base of Q2. R
2 and corresponds to the comparator 8 in FIG.
This and Q8 constitute a comparator), and its reference voltage (corresponding to 9 in FIG. 2) is applied to the pace of Q8 as Vref (1.5 V in this case).

Note that I is a constant current source. Also, when the voltage of terminal 3 is 6V, the pace voltage of Ql is set to 1.5V. R
The ratio of 2 has been determined. With the above connection, terminal 3 is 6V
In the following cases, Q8 is ON and Q4. The differential amplifier consisting of Q5 operates, and conversely, when 6V or more (7), HQ7 becomes O.
NL, Q2. It also has the function of an electronic switch that operates a differential amplifier consisting of Q3. The collector of Q5, which corresponds to the negative polarity output of the differential amplifier 2 in FIG. 2, and the collector of Q2, which corresponds to the positive polarity output of the differential amplifier 6 in FIG. The signal is amplified by an inverting amplifier, and multiple outputs can be obtained from terminal 4.

Therefore, when the voltage at the terminal 3 is 2 to 6 V, it operates as a positive polarity amplifier, and when it is 6 V or more, it operates as a negative polarity amplifier.

The present invention is not limited to the embodiments; for example, level shifting may be performed by resistor division, or other types of level shifting circuits may be used. As the electronic switch, a method of pulling up the emitter of a differential amplifier to turn it off, or another method may be used.

According to the present invention, the performance/price ratio can be improved.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional differential amplifier; Figure 2 is a block diagram showing a conventional differential amplifier;
FIG. 3 is a block diagram 9 circuit diagram showing an embodiment of the present invention. 1...IC12...Differential amplifier, 3.
...Input terminal, 4, 5...Output terminal, 6
... Differential amplifier, 7 ... Level shift circuit, 8 ... Voltage comparator, 9 ... Reference voltage source, 10 ... Electronic switch, Q1~Q9・
...Transistor, ■1 to R6...Resistor, ■...Constant current source, vref...Reference voltage, zD...Zener diode.

Claims (1)

[Claims] The first polarity input terminal of each of the first and second differential amplifiers and the second polarity input terminal of each of the first and second differential amplifiers are formed as a pair, and at least one of them is connected via a level shift circuit, and the other An amplifier circuit characterized in that one of outputs of different polarities of the first and second differential amplifiers is selectively switched and outputted to the output terminal.