JPH0528596Y2 - - Google Patents

Description

[Detailed explanation of the idea]

Industrial Application Fields This invention can be used, for example, in audio equipment such as tape recorders, tape players, tape decks, etc., to electronically switch playback channels and select a desired frequency correction for the output of the selected channel. The present invention relates to a signal processing circuit. Conventional technology Magnetic tapes include popular types of general tape,
Various tapes with different frequency characteristics are commercially available, such as low noise, high output tape, high performance tape such as chrome tape using chromium oxide, and recording signals recorded on these magnetic tapes. When reproducing a magnetic tape, it is necessary to apply a desired frequency correction to faithfully reproduce the frequency characteristics of each magnetic tape. Further, tape recorders and playback-only tape players used for recording or playing back magnetic tapes are compatible with at least two recording channels, and channel switching is required in recording or playback mode. Conventionally, in audio equipment such as tape recorders, tape players, and tape decks, switching circuits for switching channels, switching characteristics corresponding to magnetic tapes, etc. are constructed using mechanical multi-contact switches. Problems that the invention aims to solve When switching between multiple channels or modes using such a mechanical switch, the number of contacts is large, making it expensive, and wear of the contacts over long periods of use reduces switching reliability. Even if the device is constructed from a semiconductor integrated circuit, the switching circuit is a separate component, which has drawbacks such as hindering miniaturization and increasing the number of components. Furthermore, when such a mechanical switch is used, it is not suitable for arithmetic processing such as storing switching modes and selecting them based on switching control inputs. Therefore, this invention aims to provide an amplifier in which channel switching, mode switching, etc. are made electronic, and mechanical contact parts are reduced. Means for Solving the Problems The signal processing circuit of this invention includes a first amplifier (amplifier 4A) receiving a first input signal from a first signal source (magnetic head 2A), and a second signal source (magnetic head 2A). a second amplifier (amplifier 4B) that receives a second input signal from the magnetic head (magnetic head 2B), amplifies the output of the first or second amplifier, and imparts specific frequency characteristics to the output side; Filter circuit 30
A third amplifier (buffer circuit 26) to which is connected
and the first, whose emitters are shared and form a differential pair.
second, third and fourth transistors 16, 18,
20 and 22, the bases of the first and second transistors are shared, and the first switch 24
Depending on the high level voltage or low level voltage, the bases of the third and fourth transistors are made common and a constant DC voltage (bias voltage) lower than the high level voltage and higher than the low level voltage is applied.
V _B ), and the first and second transistors or the third and fourth transistors are selectively switched to a conductive state. a first current mirror circuit 6A that uses a current source (constant current source 14) to flow an operating current from the current source to the first amplifier when the fourth transistor is in a conductive state; A second current mirror circuit 6 which has a current source connected to a switch circuit and causes an operating current to flow from the current source to the second amplifier when the second transistor is in a conductive state.
B, a second switch circuit 42 connected to the filter circuit and causing the filter circuit to enter an active state when the first transistor or the third transistor is in a conductive state;
The second switch 48, 50 is added to the switch circuit to arbitrarily release the conduction state. Accordingly, this invention operates a desired amplifier by selectively passing an operating current from the first switch circuit to one or more of the one or more amplifiers based on the first switching input. and performs a desired frequency correction on the amplified output based on the second switching input. Embodiments Hereinafter, embodiments of this invention will be described in detail with reference to the drawings. The figure shows an embodiment of the signal processing circuit of this invention.
This embodiment is a signal processing circuit in a tape player. This signal processing circuit sets frequency correction switching to four modes for switching two channel signal systems. That is, the magnetic heads 2A and 2B constitute the first and second signal sources of a two-channel signal system, and a constant bias voltage V _B is applied to the common connection point of each magnetic head 2A and 2B. The reproduced signals generated at the output terminals of the magnetic heads 2A and 2B are transmitted to the first and second channels installed for each signal system.
It is applied to the non-inverting input terminals (+) of amplifiers 4A and 4B. Each of the amplifiers 4A and 4B is a differential amplifier whose amplification gain can be adjusted by adjusting the operating current. Each amplifier 4A, 4B has first and second current mirror circuits 6A, 6B that flow an operating current through a transistor as a constant current source installed inside the amplifier 4A, 4B.
is added, and each current mirror circuit 6A, 6B
is composed of transistors 8 and 10. That is, a constant current from the constant current source 14 flows into the transistor 8 side of the current mirror circuits 6A and 6B via the first switch circuit 12, and the current flows from the transistor 10 to the amplifier 4A and the amplifier 4A through the current mirror effect. 4B is selectively supplied. The first switch circuit 12 has a common emitter and a first and second transistor 1.
6 and 18 have a common base, and the third and fourth transistors 20 and 22 have a common base. Transistors 16, 18
The voltage Vcc applied from a power supply connected between the power supply terminal 23 and the ground side and the ground potential are selectively applied to the bases of the transistors 20 and 22 via the first switch 24. A bias voltage V _B is set as a reference voltage.
That is, by switching the first switch 24, a constant current from the constant current source 14 is selectively passed through the current mirror circuit 6A or the current mirror circuit 6B. The output of the amplifier 4A or 4B is applied to a buffer circuit 26 as a third amplifier, and the output of the buffer circuit 26 is fed back to the inverting input terminal (-) of the amplifiers 4A, 4B to provide a predetermined signal. An equalizer circuit 28 is installed to apply frequency correction to the signals of each signal system, and a filter circuit 30 is also installed to apply frequency correction required for so-called metal tape to the signals. The signal to which is given is taken out from the output terminal 32. In this embodiment, the equalizer circuit 28 is composed of resistors 33 and 34 and a capacitor 36, and the filter circuit 30 is composed of a resistor 38 and a capacitor 40. A second switch circuit 42 is installed on the ground side of the capacitor 40 of the filter circuit 30, and in this embodiment, the switch circuit 42 is composed of transistors 44 and 46. A base current is applied from the transistor 20 of the first switch circuit 12, and
A base current is applied to the transistor 46 from the transistor 16. Further, second switches 48 and 50 are installed between the bases of the transistors 44 and 46 and the ground point, so that the supply of base current to each transistor 44 and 46 can be switched. . It is also assumed that the switches 24, 48, and 50 are constituted by mechanical switches or semiconductor switches on a semiconductor integrated circuit. The operation will be explained based on the above configuration. When the switch 24 is closed to the a-side contact, the base potential of the transistors 16 and 18 rises higher than that of the transistors 20 and 22, so the transistors 16 and 18 are cut off, and the constant current supplied from the constant current source 14 is , transistor 2
Flows to the 0, 22 side. The constant current flowing through the transistor 22 flows to the current mirror circuit 6A side and provides an operating current to the amplifier 4A, so that the amplifier 4A becomes operational, and after the reproduced signal obtained from the magnetic head 2A is amplified by the amplifier 4A, the buffer is circuit 2
6. At this time, due to the cut-off state of the transistor 18, the current mirror circuit 6
Since no constant current is applied to amplifier B, the operation of amplifier B is stopped. Therefore, in this case, only the signal system on the A channel side is in the operating state. Further, the constant current flowing through the transistor 20 flows to the transistor 44 side of the second switch circuit 42, and when the switch 48 is open, the transistor 44 becomes conductive, so that the buffer circuit 26
A filter circuit 30 is added to the output side of the buffer circuit 26, and the signal passing through the buffer circuit 26 is subjected to frequency correction compatible with metal tape. Further, when the switch 24 closes to the b side contact, the base potential of the transistors 16 and 18 becomes lower than that of the transistors 20 and 22, so the transistors 16 and 18 become conductive instead of the transistors 20 and 22, so that the amplifier When the operating current of 4 A is released, the operating current flows from the transistor 18 to the amplifier 4B via the current mirror circuit 6B, and the amplifier 4B becomes in an operating state. In this case, only the signal system on the B channel side becomes operational. At this time, transistor 2 is connected to transistor 44.
When the current applied from 0 is released and a constant current flows from the transistor 16 to the transistor 46 side, and the switch 50 is open,
A predetermined frequency correction is applied from the filter circuit 30 to the signal passing through the B channel signal system. There is a mode in which the switches 48 and 50 are both closed or both open for switching channels A and B. In the mode where the switches 48 and 50 are both open, a predetermined frequency correction is applied from the filter circuit 30, and the switches 48 and 50 are both closed. In this mode, filter circuit 3
No such correction of 0 is applied, and the characteristics correspond to a normal magnetic tape. The switching patterns for channel switching and mode switching are as shown in Table 1.

[Table] Furthermore, since this signal processing circuit includes an equalizer circuit 28, frequency correction is performed on the signal output of each signal system regardless of mode switching. In the embodiment, a magnetic head was set as the signal source and a two-channel signal system was explained, but this invention can be applied to any signal source and can also be applied to multiple signal systems with three or more channels. It is adaptable and can be used for frequency characteristic correction other than frequency correction of metal tapes, etc. Effects of the invention As explained above, this invention provides the following effects. (a) The number of mechanical contacts can be reduced and the circuit configuration can be simplified, resulting in lower costs and improved switching reliability. (b) It is possible to have a circuit configuration suitable for semiconductor integrated circuits, and for example, by cooperating with a channel selector circuit, any mode can be stored and used to select a desired mode.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the signal processing circuit of this invention. 2A...magnetic head (first signal source), 2B...
...Magnetic head (second signal source), 4A...First amplifier, 4B...Second amplifier, 6A...First current mirror circuit, 6B...Second current mirror circuit, 12... First switch circuit, 14... constant current source (current source), 16... first transistor,
18... second transistor, 20... third transistor, 22... fourth transistor, 24
...First switch, 26...Buffer circuit (third amplifier), 30...Filter circuit, 42...
Second switch circuit, 48, 50... switch (second switch).

Claims (1)

[Claims for Utility Model Registration] A first amplifier receiving a first input signal from a first signal source; a second amplifier receiving a second input signal from a second signal source; a third amplifier connected to a filter circuit that amplifies the output of the first or second amplifier and imparts a specific frequency characteristic to the output side; a first amplifier that has a common emitter and forms a differential pair; second, third and fourth transistors, the bases of the first and second transistors are made common and a first switch causes a high level voltage or a low level voltage to be applied to the third and second transistors; The bases of the No. 4 transistors are shared and a constant DC voltage lower than the high level voltage and higher than the low level voltage is applied to the bases of the first and second transistors or the third and fourth transistors. a first switch circuit that is selectively switched into conduction; and a current source connected to the first switch circuit; when the fourth transistor is conductive, the current source connects the first amplifier to a first current mirror circuit that supplies an operating current to the second amplifier; and a current source connected to the first switch circuit, the current source transmits an operating current to the second amplifier when the second transistor is in a conductive state. a second current mirror circuit that allows current to flow; and a second switch circuit that is connected to the filter circuit and shifts the filter circuit to an active state when the first transistor or the third transistor is in a conductive state. and a second switch that is added to the second switch circuit to arbitrarily release the conduction state of the second switch circuit.