JPH0520795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multiplication circuit that multiplies two analog signals.

〔overview〕

The present invention inputs a first input signal to a first differential circuit having a load diode, a second input signal to a second differential circuit, and inputs their outputs to a bidifferential circuit. Then, the multiplication output of the first and second input signals is obtained. In the analog signal multiplication circuit, by providing a third differential circuit that performs differential amplification in place of the first differential circuit and its switching control means when the first input signal is at a low level, It is designed to operate satisfactorily even with low-level input signals.

[Conventional technology]

The conventional multiplier circuit, as shown in FIG.
18, a first input signal source 20
The first input signal 20a is input to the input terminal 24 of the differential circuit 22, and the differential circuit 22 consists of transistors 1 and 2, differential emitter resistors 3 and 4, and a constant current source 5. The output of 22 is taken out from the collectors of transistors 1 and 2 and input to the input terminal of a double differential circuit 23.

The double differential circuit 23 includes transistors 8, 9, 10
and 11, a second input signal 21a from a second input signal source 21 is input to an input terminal 25 of a differential circuit 27, which includes transistors 12 and 13, a differential emitter resistor 14 and 15, consists of a constant current source 16, and outputs a first input signal 20a and a second input signal 21 from an output terminal 26.
A multiplication output 26a, which is the product of a and a, is output. Note that 28 is a power supply terminal.

[Problems to be Solved by the Invention] In the conventional analog signal multiplication circuit described above, since the load of the differential circuit 22 is the load diodes 6 and 7, the linearity of the multiplication output is wide with respect to the input signal level. In order to remain within a range, the level of the input signal is limited to a certain range of magnitude.

By the way, in order to realize a detection operation such as FM demodulation using four-phase phase detection using this conventional circuit, transistors 8, 9, 1 of the double differential circuit 23 must be
An input signal of sufficient level must be provided to cause complete switching of 0 and 11.
However, if the input signal is small, this level may not be satisfied. Therefore, the conventional circuit in which the input signal level range is limited as described above has the disadvantage that operation at low levels is insufficient and detection cannot be performed by the switching operation as described above.

An object of the present invention is to provide a multiplication circuit that can operate satisfactorily regardless of the level of the input signal by eliminating the above-mentioned drawbacks.

[Means for solving problems]

The present invention includes: a first differential circuit having a load diode and having an input connected to a first input signal; a second differential circuit having an input connected to a second input signal;
A multiplication circuit including a double differential circuit to which the outputs of the first and second differential circuits are connected together and outputs a multiplication output of the first input signal and the second input signal, a third differential circuit having a load circuit connected to the first input signal and having an output connected to the input of the bi-differential circuit and having a characteristic different from that of the load diode of the first differential circuit;
The present invention is characterized in that it includes a switching control means for switching between the first differential circuit and the third differential circuit depending on the level of the first input signal.

[Effect]

The present invention includes a first differential circuit having a load diode, a third differential circuit having a level characteristic that is different from the characteristic of the load diode and extends to a lower level side, and a load circuit with a large load. , are switched and operated in accordance with the level of the first input signal. That is, when the first input signal is at a low level, the third differential circuit is operated, and when the first input signal is at a high level, the first differential circuit is operated as before.

This makes it possible to operate sufficiently even when the input signal, which has conventionally been insufficiently operated, is at a low level.

The load circuit described above only needs to have a large load extending to the low level side with respect to the load characteristics of the load diode of the first differential circuit, for example, a resistor, a series connection circuit of a diode and a resistor, or a diode with different characteristics. Any of these circuits performs the same function.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In this embodiment, the load diode 106
and 107, and a first input signal 120a from a first input signal source 120 is connected to an input terminal 124; a second differential circuit 127 to which a second input signal 121a is connected; and a first input signal 12 to which the outputs of the first and second differential circuits 122 and 127 are connected.
Multiplication output 12 of 0a and second input signal 121a
6a from the output terminal 126
23, the first input signal 120a is connected to the input, the output is connected to the input of the double differential circuit 123, and the load diodes 106 and 107 of the first differential circuit 122 are connected.
A third differential circuit 138 having load circuits 131 and 132 with different characteristics, and a first differential circuit 12 and a third differential circuit 127 are switched and used depending on the level of the first input signal 120a. It also includes a control circuit 130 as a switching control means.

Note that 128 is a power supply terminal, 129 is a control terminal, and the two outputs of the control circuit are respectively connected to the transistor 1 that constitutes the constant power supply of the first differential circuit 122.
05 and the base of a transistor 137 that constitutes a constant power source of the third differential circuit 138.

The feature of the present invention is that in FIG.
This is because a third differential circuit having circuits 31 and 132 and a control circuit 130 are provided.

Next, the operation of this embodiment will be explained. A first input signal 120 from one input signal source 120
a is input to the differential circuits 122 and 138 from the input terminal 124, and the output of the differential circuit 122 is taken out from the collectors of the transistors 101 and 102, and is input to the bidifferential circuit 132 through the load circuits 131 and 132. and the second input signal 121a from the other input signal source 121 is
The signal is input to the input terminal 125 of the differential circuit 127, the first input signal 120a and the second input signal 121a are multiplied by the bi-differential circuit 123 and the differential circuit 127, and the multiplication output is output from the output terminal 126. 123a
is taken out.

The control circuit 130 controls the transistor 105 in response to a control signal input to an external control terminal 129.
and 137 is turned on or off. Now, the first input signal 120a
When the level of transistor 10 is high level,
5 is turned on and the transistor 137 is turned off, the first input signal 120a and the second input signal 121a are multiplied as before, as described above.

Next, if the transistor 137 is turned on and the transistor 105 is turned off when the first input signal 120a is at a low level, the differential circuit 138 operates. The differential circuit 138 is composed of transistors 133, 134, and 137, and differential emitter resistors 135 and 136. , the load circuits 131 and 132 can be made larger. Therefore, the output of the differential circuit 138 can be increased. Therefore, the differential circuit 138
A large output is input to the bi-differential circuit 123, and a sufficiently multiplied output 126a of the first input signal 120a and the second input signal 121a is taken out from the output terminal 126.

At this time, the transistor 10 of the double differential circuit 123
8, 109, 110, and 111 mutually perform a switching operation to detect the second signal 121a input to the differential circuit 127 at the frequency of the first input signal 120a input to the differential circuit 138. conduct.

〔Effect of the invention〕

As explained above, the present invention provides a third differential circuit that performs differential amplification in place of the first differential circuit when the first input signal is at a low level, and a switching control means therefor. , there is an effect that a multiplication output can be obtained regardless of the level of the first input signal.

Therefore, the multiplier circuit according to the present invention can also be used as a four-phase phase detector, so that, for example,
In the recording mode of the VTR signal processing circuit, the phase detection of the chroma signal can be performed, and in the video mode, it can be used as part of the AGC amplifier for the reproduced chroma signal, resulting in a multifunctional multiplication circuit.

Furthermore, if the present invention is applied to a semiconductor integrated circuit, elements can be shared, and external terminals can also be shared, which has the additional effect of facilitating integrated circuit implementation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Second
The figure is a circuit diagram showing a conventional example. 1, 2, 8-13, 101, 102, 105,
108-113,133,134,137...transistor, 3,4,14,15,103,10
4,114,116,135,136... Differential emitter resistance, 5,16,116... Constant current source, 6,
7, 106, 107...Load diode, 17, 1
8,117,118,131,132...Load circuit, 19,119...Level shift circuit, 20,2
1, 120, 121...input signal source, 20a, 21
a, 120a, 121a...input signal, 22, 2
7, 122, 127, 138...differential circuit, 23,
123...double differential circuit, 24, 25, 124, 12
5...Input terminal, 26, 126...Output terminal, 26
a, 126a... Multiplier output, 28, 128... Power supply terminal, 129... Control terminal, 130... Control circuit.

Claims (1)

[Claims] 1. A first differential circuit having a load diode and having an input connected to a first input signal; a second differential circuit having an input connected to a second input signal; A multiplication circuit including a double differential circuit whose inputs are connected to both the outputs of the first and second differential circuits and which outputs a multiplication output of the first input signal and the second input signal, the input comprising: a third differential circuit having a load circuit connected to the first input signal and having an output connected to the input of the bi-differential circuit and having a characteristic different from that of the load diode of the first differential circuit; A multiplication circuit comprising switching control means for switching between the first differential circuit and the third differential circuit depending on the level of the first input signal.