JPS6110340Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching amplifier, and more particularly to a single-ended or balanced broadband amplifier that selectively amplifies and transfers an input signal to an output terminal.

Switching amplifiers are widely used in various electrical/electronic equipment, but especially in electronic measurement equipment such as oscilloscopes, switching amplifiers select multiple input signals applied to multiple input terminals and output one or more of them. Many are used to amplify and transmit common loads. For example, in the case of a two-phenomenon oscilloscope, the input signal of channel 1 or 2 may be selectively transmitted to a common vertical amplifier, or an internal trigger signal derived from the signal of channel 1 or 2 may be used in a synchronous relationship with the input signal of channel 1 or 2. It is used to selectively supply some external trigger signal or line periodic signal related to the power supply frequency to the trigger pulse regeneration circuit. Such an amplifier can also be used in the so-called "external trigger signal observation mode" in which an external trigger signal is applied to the vertical input circuit as required. Regarding this mode, please refer to the patent application filed in 1973.
No. 76107 "Oscilloscope" is disclosed in sufficient detail, so please refer to the specification.

An example of such an amplifier is shown in block diagram form in FIG. The two input signals applied to input terminals 10 and 12 are transmitted via switching amplifiers 14 and 16, respectively, to a common output amplifier 18 and then to output terminal 20. The switching amplifiers 14, 16 are controlled by a control logic circuit 24 which may be a flip-flop operating under the control of a control signal applied to a control terminal 22. For example, when the Q output of the logic circuit 24 is high and the output is at a low level, the channel 1 signal applied to the terminal 10 is amplified and transmitted to the output amplifier 18, while the channel 2 signal applied to the terminal 12 is blocked (blocked). be done. On the other hand, when the output of the logic circuit 24 is inverted, the channel 2 signal is selectively amplified and transmitted to the output amplifier 18.

An electrical circuit diagram of a conventional example of such a switching amplifier is shown in FIG. In the balanced amplifier of FIG. 2, the amplifier circuit 30 includes a pair of common base transistors 3.
4, 34' and a switching circuit 32,
Input terminals 26, 26' and output terminals 28, 2, respectively.
8' are connected in series. Switching circuit 32
are two diodes 36, 36' in series with the signal path.
and two diodes 38, 38' in parallel. parallel diode 3
A control signal is applied to the common connection point 40 of the diodes 38, 38' or 36, 36' alternately on or off depending on the control voltage.
When series diodes 36, 36' are on and parallel diodes 38, 38' are off, transistor 3
4, 34' collector current is output terminal 28, 2
8'. On the other hand, the diode 36,3
When 6' is off and diodes 38, 38' are on, the collector signal current is short-circuited and cannot reach the output terminals 28, 28'. However, the inductance associated with each of these switching diodes leaks, especially at high frequencies. This signal leakage is caused by transistors 34 and 3 when no signal transmission is desired.
It can be reduced somewhat by turning off 4'. For this purpose, transistors 34,3
A switch 46 and a diode 48 are connected to both transistors 34, 3, in addition to voltage divider resistors 42, 44 which normally apply a forward bias voltage to the bases of transistors 4'.
4', which closes switch 46 and raises the base voltage of transistors 34 and 34', turning them off.

The case of FIG. 2 has the disadvantage that the circuit configuration is complicated and many circuit elements are required.

It is therefore an object of the invention to provide a switching amplifier that does not have the drawbacks of conventional circuits.

The switching amplifier of the present invention will be explained in detail below with reference to FIGS. 3 and 4. 3A to 3C show different embodiments of the switching amplifier of the present invention. The first two are single-ended, and the last is balanced. FIG. 4 shows a practical balanced amplifier circuit including a switching amplifier according to the present invention.

In the embodiment of FIG. 3A, the first transistor 50
The main current path, that is, the emitter collector is the input terminal 2.
6 and the output end 28. The emitter of a second transistor 52 having the same conductivity type as the first transistor 50 is connected to a reference potential source (a chassis potential in this embodiment), and the collector is connected to a positive power source via a load resistor 58. A diode 54 is connected between the collector and emitter of the second transistor 52.
Further, the other diode 56 is connected to the second transistor 5
2 and the emitter of the first transistor 50, and this emitter is further connected to a negative power supply via a bias resistor 60. The bases of the first and second transistors 50, 52 are connected together to form a control terminal 62, which is connected to control logic represented by a switch 64 and a pull-up resistor 66.

The operation of the switching amplifier shown in FIG. 3A is as follows. When the control signal is high, i.e., switch 64 is off, second transistor 52 is forward biased, thus transistors 50, 52
The base voltage of transistor 52 is approximately +0.7 volts, and the collector voltage of transistor 52 is approximately 0 volts. Therefore, the first transistor 50 is conductive (on) and its emitter voltage is approximately 0 volts, so that
Both diodes 54 and 56 are off. The input signal is then transmitted to the output terminal 28 substantially without loss. The reason for this is that under this condition, the input impedance of transistor 50 is extremely low, and since diode 56 is off, it has a high impedance and substantially no signal flows.
When the control voltage is at a low level, i.e., switch 64 is on, second transistor 52 is off and the current flowing through load resistor 58 is diverted from diodes 54 and 5.
Flows through 6. These diodes 54, 56 provide a low impedance signal path and maintain the emitter voltage of first transistor 50 at approximately 0 volts.
Under this condition, the base-emitter voltage is 0 volts, so the first transistor 50 is just turned off.

As can be seen from the above description, by applying a logic high or low level to the control terminal 62, the series signal path (first transistor 50) or the parallel signal path (diodes 54, 56) can be selectively turned on and off. The input signal is selectively amplified and transmitted to the output terminal 28. The emitter voltage of the first transistor 50, ie, the voltage at the input terminal 26 which is the output voltage of the preamplifier, is a constant value of approximately 0 volts regardless of the switch state. Furthermore, first and second transistors 50,
52 effectively avoids being excessively reverse biased, thus maintaining maximum switching speed.

Figure 3B shows the first and second transistors.
This is a single-ended switching amplifier similar to the embodiment of FIG. 3A except that PNP transistors are used. Since this circuit operates in substantially the same manner as in FIG. 3A, no special detailed explanation is considered necessary.
The emitter voltage of the first transistor 50 also remains at a constant value of approximately 0 volts.

Figure 3C is a balanced switching amplifier, similar to Figure 3A except that transistor 50', diode 56' and bias resistor 60' are added.
It is similar to the amplifier of A push-pull input signal is applied to the input terminals 26, 26' which is selectively transmitted to the output terminals 28, 28'. A control signal to control terminal 62 causes parallel path diodes 56-56'
When turning off (or on) the series path transistors 50-50' can be turned on (or off). That is, when the control terminal 62 is at a high level, the transistor 52 is turned on, and the transistors 50,
The base potential of 50' and 52 is approximately +0.7 volts. The emitter potential of transistors 50, 50' is approximately 0 volts, and diodes 54, 56 and 5
6' are both off. On the other hand, when the control voltage is at a low level, the transistor 52 is turned off and the current flowing through the resistor 58 is partially transferred to the diode 5.
4 and the rest are diodes 56, 56'.
Furthermore, it flows through resistors 60, 60' to the negative power supply. Therefore, since the collector voltage of transistor 52 is approximately +0.7 volts, transistors 50,
The emitter voltage of 50' is approximately 0 volts as before. This means that all of the effects described above with respect to FIG. 3A also apply to FIG. 3C. Of course, in the circuit of FIG. 3C, a balanced switching amplifier similar to that of FIG. 3B can also be obtained by changing all the transistors to PNPs and changing the polarities of the diodes and power supply.

FIG. 4 shows an example of a practical circuit of a balanced amplifier including the switching amplifier of the present invention. Of the two switching amplifiers 68 and 70 used, only the former is shown in detail, but both may have the same circuit configuration, and three or more switching amplifiers may be used as necessary. 1 in the latter case
The portion may be a conventional circuit as shown in FIG. The outputs of the switching amplifiers 68, 70 are connected to two stages of common emitter transistors 74-74' and 76-7.
6' and feedback resistors 78-78'. This output amplifier 18
The bases of transistors 74-74' forming the inputs of are interconnected through a pair of equal resistors 80-80'. The collectors of transistors 76-76' form output terminals 28, 28' and are interconnected through a pair of resistors 82-82'. A DC level correction circuit including an operational amplifier 84 and an emitter follower transistor 86 is connected between the midpoints of resistors 80-80' and 82-82'.

To explain the operation, when the switch 64 is off, that is, the control signal is at a high level, the input terminal 26-2
A first input signal applied between terminals 6' and 6' can be selected, and this signal is transmitted to output amplifier 18. The voltage gain of such an amplifier circuit is approximately determined by the resistance ratio of the feedback resistors 78, 78' and the input resistors 61, 61'. Similarly, when second switching amplifier 70 is enabled, a second input signal applied across input terminals 72-72' is amplified and appears at output terminals 28-28'. Of course, the switch 64 of the first switching amplifier 68 is disabled in this state.
It is. As mentioned above, the unselected input signals are completely shunted by the parallel path diodes 56-56' and do not leak to the output terminal, so that no signal interference occurs. A feedback path including operational amplifier 84 maintains the average DC level at output terminals 28-28' at a constant value, zero volts in this embodiment.

As is clear from the above description and the accompanying drawings, the switching amplifier according to the present invention basically uses two transistors of the same conductivity type, two diodes, and a small number of passive elements, and in order to make it a balanced type, It is composed of three transistors of the same conductivity type, three diodes, and a small number of passive elements. The use of a transistor in a series signal path and a diode at its emitter as a parallel signal path ensures complete transmission or interruption of the input signal depending on the control signal without substantially changing the emitter voltage. Can be done. An optimum bias is applied to the base-emitter junction of this switching transistor, thereby ensuring optimum operation. Additionally, since the amplifier can be directly controlled by logic circuits, remote control is possible.

It should be noted that although the above explanation has been made only regarding the preferred embodiments of the present invention, the present invention is not limited to such embodiments in any way, and those skilled in the art will be able to understand the specific embodiments based on the gist of the present invention. It is easy to understand that optimal changes and modifications can be made depending on the application. Therefore, it should be understood that the technical scope of the present invention naturally includes such changes and modifications.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an application example of the switching amplifier of the present invention, FIG. 2 is a circuit diagram of a conventional switching amplifier, FIGS. 3A to C are circuit diagrams of a preferred embodiment of the switching amplifier of the present invention, and FIG. FIG. 4 is a practical amplifier circuit diagram including a switching amplifier according to the present invention. In the figure, 50 (or 50') is the first transistor, 52 is the second transistor, 56 (or 5
6') represents a first diode, and 54 represents a second diode.

Claims (1)

[Scope of utility model registration request] a first transistor whose emitter and collector are connected to input and output terminals, respectively; and a first transistor whose base and collector are connected to a desired power source via the base and resistor of the first transistor, respectively, and whose emitter is connected to a reference potential source. a second transistor of the same conductivity type as the first transistor; and first and second diodes connected in series in opposite directions between the emitter of the first transistor and a reference potential source, with their midpoints connected to the collector of the second transistor; Equipped with
A switching amplifier configured to control base voltages of the first and second transistors.