JPH04278708A - Gyrator - Google Patents

Abstract

PURPOSE:To extend the input dynamic range and to prevent oscillation. CONSTITUTION:Output circuits 34 and 38 consisting of emitter follower circuits are installed on the output sides of gyration admittance cells Gm 32 and 36 which give an inductance characteristic to an input signal, and active circuits 330 and 370 are installed as loads of transistor differential pairs 320 and 360 constituting gyration admittance cells.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gyrator used as a built-in filter in an IC.

0002

[Prior Art] Conventionally, a gyrator has a gyration admittance cell (hereinafter referred to as "Gm") as shown in FIG.
2 and 4 (referred to as "cell") and a full feedback buffer circuit 6. That is, the Gm cells 2 and 4 are connected in series, the full feedback buffer circuit 6 is installed on the output side of the Gm cell 4 on the subsequent stage, and the output of the full feedback buffer circuit 6 is connected to each Gm cell.
It is configured to feed back to the negative phase input side of the m cells 2 and 4. This gyrator has capacitors connected to terminals 8, 10, 12, and 14, respectively, to form a filter. Therefore, when an input signal Vi is applied to the input terminal 12, an output signal Vo of a specific frequency component is obtained at the output terminal 14.

[0003] This gyrator is constructed as shown in FIG. 5, for example. That is, a pair of transistors 21 and 22 are installed in the Gm cell 2, and the emitters of each transistor 21 and 22 are coupled via a diode, that is, transistors 23 and 24 having a common base and collector. Transistors 21 and 22 form one transistor differential pair 25 via transistors 23 and 24.
It consists of A constant current source 26 through which an operating current flows is connected to the emitter side of each transistor 23, 24. The collector of the transistor 21 is directly connected to the power supply line 16, and the collector side of the transistor 22 is connected to a constant current source 27. If the constant current set in the constant current source 26 is I, then the constant current of the constant current source 27 is I/2
is set to . Similarly, the Gm cell 4 installed at the next stage of the Gm cell 2 has transistors 41, 42, 43,
44, a transistor differential pair 45, a constant current source 46,
47, and the relationship between constant currents I and I/2 is also the same.

Next, the full feedback buffer circuit 6 is provided with a transistor differential pair 63 consisting of a pair of transistors 61 and 62 whose emitters are directly connected. A constant current source 64 is installed on the side. transistor 61
Like the Gm cells 2 and 4, the collector is directly connected to the power supply line 16 side, and a constant current source 65 is installed on the collector side of the transistor 62. The output of the full feedback buffer circuit 6 is taken out from the collector side of the transistor 62, fed back to the base of the transistor 62 via the base-emitter of the transistor 66, and taken out from the output terminal 14. A constant current source 67 for passing an operating current through the transistor 66 is connected to the emitter side of the transistor 66 . Also in this full feedback buffer circuit 6, a constant current I is set to the constant current source 64,
A constant current I/2 is set to the constant current source 65. Then, the output of the total feedback buffer circuit 6 is
, 4 are fed back to the bases of the transistors 22, 42.

[0005]

By the way, in such a gyrator, the Gm cells 2 and 4 are directly connected and the full feedback buffer circuit 6 is installed on the output side to form the feedback circuit 18. Since the paths are tripled and oscillation is very likely to occur, it is difficult to handle, and furthermore, the input dynamic range is small and linearity can only be achieved within a narrow range, so there are disadvantages such as a limited range of use.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a gyrator which has an expanded dynamic range and is less likely to cause oscillation.

[0007]

[Means for Solving the Problems] That is, the gyrator of the present invention provides gyration admittance cells (Gm cells 32, 3
6) is characterized in that an output circuit (34, 38) consisting of an emitter follower circuit is installed on the output side.

The gyrator of the present invention also has a diode (transistors 323, 324 or transistors 363, 3) connected between the emitters of a pair of transistors (transistors 321, 322 or transistors 361, 362).
64 or transistors 331, 332, 334, 335
or a differential pair formed by coupling with transistors 371, 372, 374, 375 interposed
20, 360) and an active circuit (330, 370) as a load.
) are connected to the gyration admittance cells (Gm cells 32, 36), and the operating current is caused to flow by a constant current source (325, 365), and the output of the gyration admittance cells is received from the active circuit. , and an output circuit (34, 38) consisting of an emitter follower circuit for taking out the output.

[0009]

[Operation] By installing an output circuit consisting of an emitter follower circuit on the output side of the gyration admittance cell, a full feedback buffer circuit is no longer required.・When using an admittance cell and output circuit,
Although the feedback path is doubled, the number of feedback paths is reduced compared to a conventional gyrator using a full feedback buffer circuit.
This makes it difficult to oscillate.

Furthermore, by installing an active circuit with the gyration admittance cell as a load in the differential pair, the circuit symmetry of the gyration admittance cell is improved, that is, the current between the transistors constituting the differential pair is increased. Balance is improved and input dynamic range linearity is improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the gyrator of the present invention. This gyrator includes a first Gm cell (gyration admittance cell) 32 and its output circuit 34 on the first stage side, and a second Gm cell (gyration admittance cell) 36 and its output circuit 38 on the next stage side.
is installed. Each Gm cell 32, 36 is for obtaining desired inductor characteristics. In order to configure a filter to be built into the IC and obtain desired frequency characteristics, this gyrator is connected to terminals 40 and 42 with capacitors CA and CB (not shown), and also to an input terminal 46 and an output terminal 48 (not shown). No capacitor is connected. An input signal Vi from which a desired frequency component is to be extracted is applied to the input terminal 46, and an output signal Vo having the desired frequency component is obtained at the output terminal 48.

The output circuit 34 is an output extraction means of the Gm cell 36 for inputting the output of the Gm cell 32 to the next stage Gm cell 36, and is installed as an impedance conversion means, and is an emitter follower. It is made up of circuits. That is, an NPN type transistor 342 is installed in this output circuit 34, and a power supply line 50 is directly connected to the collector of this transistor 342.
A constant current source 344 is connected in series between the emitter side and a ground point which is a reference potential point.

The output of Gm cell 32 is applied to Gm cell 36 through output circuit 34, and the output of Gm cell 36 is outputted by output circuit 38. This output circuit 38 is constructed of an emitter follower circuit like the output circuit 34, that is, an NPN type transistor 382 is installed in this output circuit 38.
A power supply line 50 is directly connected to the collector of , and a constant current source 384 is connected in series to the emitter side of the power supply line 50 .

The output of the output circuit 38 is taken out from the emitter of the transistor 382 through the output terminal 48 and is fed back to the Gm cells 32 and 36 via the feedback circuit 52.

With the above configuration, the input signal Vi
is applied to the Gm cell 32, and the output of the Gm cell 32, which has been given an inductance characteristic according to the input signal, is applied to the base of the transistor 342 of the output circuit 34. Then, the output of this output circuit 34 is taken out from the emitter side of the transistor 342 with its level lowered by the base-emitter voltage, and is applied to the Gm cell 36 at the next stage.

The Gm cell 36 is given an inductance characteristic according to the input from the output circuit 34, and its output is applied to the base of the transistor 382 of the output circuit 38, and the level is lowered from the emitter side by the base-emitter voltage. The resulting output Vo is taken out from the output terminal 48 and sent to each Gm cell 32, 3 through the feedback circuit 52.
He will be returned on 6th.

In this way, the output circuits 34, 38 each consisting of an emitter follower circuit are provided on the output side of each Gm cell 32, 36.
This makes it difficult to oscillate compared to a conventional gyrator equipped with a full feedback buffer circuit, resulting in stable gyration characteristics.

Next, FIG. 2 shows a specific example of the circuit configuration of the gyrator of the present invention. In the Gm cell 32, a transistor differential pair 320 is installed, in which the emitters of a pair of transistors 321 and 322 are coupled through a diode, that is, transistors 323 and 324 whose bases and collectors are connected in common. Transistors 323, 32
A constant current source 325 for causing an operating current to flow through the transistor differential pair 320 is connected in series to the emitter side of the transistor 4. Furthermore, an active circuit 330 composed of transistors 326 and 327 and resistors 328 and 329 is installed as an active load between the collector sides of the transistors 321 and 322 and the power supply line 50.

A capacitor CA (not shown) is connected to a terminal 40 on the collector side of the transistor 322 of this Gm cell 32. Further, the output taken out from the collector side of the transistor 322 is applied to the Gm cell 36 through the output circuit 34. This output circuit 34 is composed of a transistor 342 forming an emitter follower circuit and a constant current source 344 as in the previous embodiment.

Gm installed at the next stage of this output circuit 34
Cell 36 is configured similarly to Gm cell 32. That is, this Gm cell 36 includes a pair of transistors 361.
, 362 are connected by a diode, that is, transistors 363 and 364 whose bases and collectors are connected in common. A differential pair of transistors 360 is provided. A constant current source 365 is connected in series to the emitter sides of the transistors 363 and 364 for supplying operating current to the transistor differential pair 360. Furthermore, an active circuit 370 consisting of transistors 366, 367 and resistors 368, 369 is installed as an active load between the collector sides of the transistors 361, 362 and the power supply line 50.

A capacitor CB (not shown) is connected to the terminal 42 on the collector side of the transistor 367 of this Gm cell 36. Further, the output taken out from the collector side of the transistor 362 is taken out from the output terminal 48 through the output circuit 38, and the output is taken out from the Gm cell 32.
is fed back to the base of transistor 322. The output circuit 38 is composed of an emitter follower circuit including a transistor 382 and a constant current source 384, as in the previous embodiment.

According to such a configuration, the input signal Vi is applied to the transistor differential pair 320 of the Gm cell 32 through the input terminal 46 and amplified, and after being given a predetermined inductance characteristic, the input signal Vi is sent through the output circuit 34. Gm cell 36
, and is taken out from the output terminal 48 through the output circuit 38 provided with a predetermined inductance characteristic.

[0023] As described above, since the active loads by the active circuits 330 and 370 are installed in the respective Gm cells 32 and 36, the active load between the transistors 321 and 322 and the transistor 36
The current balance between 1 and 362 is improved, the input dynamic range is increased, and the linearity is improved.

Furthermore, by installing the output circuits 34 and 38 consisting of emitter follower circuits, a gyrator is constructed in which oscillation is less likely to occur compared to when a conventional full feedback buffer circuit is installed, and furthermore, the input dynamic range is The signal-to-noise ratio is also improved because the signal can be increased.

Next, FIG. 3 shows a specific example of the circuit configuration of the gyrator of the present invention. In this embodiment, the transistor differential pair 320 of the Gm cell 32 includes four sets of diodes,
In other words, the transistor 3 with a common base and collector
31, 332, 334, 335 were installed, and Gm
The transistor differential pair 360 of the cell 36 is also provided with four sets of diodes, that is, transistors 371, 372, 374, and 375 having a common base and collector.

The constant current source 325 of the embodiment described above is composed of a transistor 337 and a resistor 338, and the constant current source 365 is composed of a transistor 377 and a resistor 378.
392 and a common current source 5 consisting of resistors 393 and 394
4 is installed. That is, transistors 337, 37
7, 391, 392 and resistors 338, 378, 393,
Reference numeral 394 constitutes a current mirror circuit, and an input current corresponding to the operating current to be passed through the Gm cells 32, 36 is supplied to the input terminal 56 from an external or internal current source of the integrated circuit.

In this embodiment, the power supply for the Gm cells 32 and 36 and the power supply and grounding point for the output circuits 34 and 38 are separated from each other, and power lines 50A and 50B are connected to each other.
This is why there are two systems of ground lines 58A and 58B.

Even with this configuration, the same gyration characteristics as in the embodiment described above can be obtained, and advantages such as improvement in the linearity of the input dynamic range and suppression of oscillation can be obtained.

[0029]

[Effects of the Invention] As explained above, according to the present invention, the following effects can be obtained. a. By reducing the number of oscillation paths, oscillation can be suppressed and reliability can be improved. b. Since the symmetry of the circuit is increased, the input dynamic range can be expanded and the linearity of the input dynamic range can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a gyrator of the present invention.

FIG. 2 is a circuit diagram showing a specific example of the circuit configuration of the gyrator of the present invention.

FIG. 3 is a circuit diagram showing a specific example of the circuit configuration of the gyrator of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional gyrator.

FIG. 5 is a circuit diagram showing a specific example of the circuit configuration of the gyrator shown in FIG. 4;

[Explanation of symbols]

32, 36 Gyration admittance cell 34, 38 Output circuit 320, 360 Transistor differential pair 321, 3
22,361,362 Transistor 323,3
24,363,364,331,332,334,33
5,371,372,374,375 Transistor (diode) 325,365 Constant current source 330,370 Active circuit

Claims (2)

[Claims] 1. A gyrator characterized in that an output circuit consisting of an emitter follower circuit is installed on the output side of a gyration admittance cell that imparts inductance characteristics to an input signal. 2. A gyration admittance cell in which an active circuit is connected as a load to a differential pair formed by coupling the emitters of a pair of transistors with a diode interposed between them, and an operating current is caused to flow by a constant current source. and an output circuit comprising an emitter follower circuit that receives the output of the gyration admittance cell from the active circuit and takes out the output.