JPS5941629Y2 - active inductance circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention aims to propose an active inductance circuit which can increase the apparent inductance of the coil to a maximum width by simplifying the circuit configuration.

For example, in the audio circuit of a stereo receiver, if you are trying to construct a low-frequency cutoff filter with an extremely low cutoff frequency of, say, 200Hz and an output impedance of about 3 ρ, the inductance of the coil must be very large, on the order of several Henrys. In this case, the coil itself becomes very large, which is not practical.

In view of this, the present invention proposes an active inductance circuit that can significantly increase the apparent inductance of the coil and substantially reduce the size of the coil using a very simple circuit configuration. This is what I am trying to do.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 01 is an input terminal, and 2 is the other input terminal which is grounded.

Reference numeral 3 denotes a field effect transistor (N-channel type in this case) as an active element, whose gate, which is an input electrode, is connected to the input terminal 1, and via a coil 4 to its source, which is an output electrode.

This source is grounded through a resistor 5 and connected to an output terminal 7, and 8 is the other grounded output terminal.

A drain serving as a common electrode of the transistor 3 is grounded via a DC power supply 6.

Next, equivalent circuits of the circuit shown in FIG. 1 described above are shown in FIGS. 2 and 3, and the operation thereof will be explained using mathematical formulas.

20, 21, and 22 are external electrodes of the field effect transistor 3, namely, a gate electrode, a source electrode, and a drain electrode, respectively.

30 is a capacitance of, for example, several pF between the gate and drain of the field effect transistor 3; 31 is a leakage resistance of approximately several hundred M/) between the gate and drain of the transistor 3;
These are connected in parallel between input terminals 1 and 2.

32 is several hundred M, Q between the gate and source of transistor 3
The leakage resistance 33 is a capacitance of about several pF between the gate and source.

4 is an inductance component of the coil 4 connected in parallel between the gate and source of the field effect transistor 3, and 35 is a loss resistance valve of the coil 4, which is connected in series.

Reference numeral 36 denotes a current source in this equivalent circuit, and assuming that the mutual conductance is gm and the gate-source voltage is VGS, the electromotive voltage thereof is gm·VGS.

37 is a channel resistance of several tens of kg as an output resistance.

Reference numeral 5 denotes a source load resistance, which is connected between the output terminal 7 and the other grounded output terminal 8.

Input voltage ei is supplied between input terminals 1 and 2, and output direct pressure e is supplied between output terminals 7 and 8.

is taken out, and this voltage e.

is supplied to the load resistor 5. Next, FIG. 3 shows a simplified version of the equivalent circuit shown in FIG. 2 described above.

In FIG. 3, the same parts as in FIG. 2 will be described with the same reference numerals.

That is, in this case, only the coil 4, the loss resistance molecule 135 of its inductance L, the current source 36, the channel resistance 37, and the source load resistance 5 are configured, and the other elements of the equivalent circuit shown in FIG. It was ignored.

Next, let's take a closer look at the circuit shown in Figure 3.

The impedance Zin viewed from the input terminals 1 and 2 to the right is expressed by the following equation (1), where the input voltage is eil and the current flowing into the gate electrode 20 of the transistor 3 is Ig.

Further, the gate electrode 20 and the source electrode 2 of the transistor 3
If the voltage applied during 1 g is VGS, then 1 g of current is expressed by the following equation (2).

Also, the gate-source voltage VGS is the input voltage ei and the output voltage e.

, the ratio is AV (=-2-) and i Then, it is expressed by the following equation (3).

By substituting equation (3) into equation (2), 1 g of current is calculated as follows (4
) is expressed by the formula.

Furthermore, by substituting equation (4) into equation (1), input impedance Zin is expressed by equation (5) below.

Therefore, the equivalent circuit of FIG. 3 is further simplified and represented as the circuit of FIG. 4.

In Figure 4, there is a coil 3 between the gate and drain.
8 and a resistor 39 are connected in series, and the coil 38
The inductance value L' and the value r1' of the resistor 39 are expressed by the following (6) and (7).

Therefore, the inductance L can be substantially increased by about 100 times.

Further, Q' of this circuit is expressed as in the following equation (8).

Therefore, the equivalent inductance L' is twice the previous indenotance L, and the circuit Q' is the same as when using the original i-AV inductance.

By the way, in this embodiment, since the source follower type field effect transistor 3 is used, the voltage amplification rate A is
V is Ay61, and the equivalent inductance increases by about 100 times.

The actual value of the above-mentioned □ -AV is expressed by the following equation (9), showing only the calculation result.

Then, by setting r D 3 >> RB, equation (9) is converted to equation 00).

Therefore, according to the active inductance circuit of the present invention, the apparent inductance when looking to the right of terminals 1 and 2 is increased, for example, by about 100 times.

5 and 6 are other examples of the present invention, in which the variable resistor 14 is inserted between the source of the transistor 3 and the output terminal 7 in FIG. 1 in FIG. In the figure, the resistor 5 is constructed from a variable resistor.

Even in the case of collapse, the inductance of the circuit on the right side from the input terminal 1.degree. 2 can be easily and continuously varied by adjusting the variable resistor 8 or 5.

FIG. 7 shows another example of the present invention, in which a bipolar transistor 9 is provided in place of the field effect transistor 3 as an active element.

Bipolar transistor 9 is field effect transistor 3
Unlike this, it is necessary to supply bias from the power supply 6 to the base, which is the input electrode.

Therefore, a resistor 10 connected in series in parallel with the power supply 6,
11, a coil 8 is connected between the midpoint of the connection and the base, which is the input electrode of the transistor 9, and a capacitor 12 is connected between the midpoint of the connection and the emitter, which is the output electrode.

Since the operation of this circuit is considered to be almost the same as that using the field effect transistor shown in FIG. 1, its explanation will be omitted.

Note that when the bipolar transistor 9 is used as an active element, its base resistance rb, emitter resistance re, and emitter resistance RE (resistance of the resistor 5) are connected in parallel to the inductance 4, and the transistor 9 hfe, its total impedance Z
In is Zin=rb+hfe(re+RE).

(5) Equation (7) Zi. −r1+jG)L,. ratio,
Since the output voltage can be set to 60-AV, the above-mentioned resistances can be substantially ignored.

Next, an application example of the present invention will be explained with reference to FIGS. 8, 9, and 10.

FIG. 8 shows an example in which the present invention is applied to a bypass filter, in which the active inductance circuit of the present invention is inserted in the position where a coil is normally placed.

42 and 43 are series-connected capacitors constituting a bypass filter, both ends of which are connected to the input terminal 40 and the output terminal 41.

The connection midpoints of the capacitors 42 and 43 are connected to the gate of the field effect transistor 3 and one end of the coil 4, and the source of the transistor 3 is connected to the other end of the coil 4 and grounded via the variable resistor 5. .

Then, a transistor 3, a coil 4, a variable resistor 5. Since the power supply 6 constitutes an active inductance circuit, by adjusting the variable resistor 5, the inductance of the bypass filter can be changed and its cutoff frequency can be controlled.

Note that 44 is a signal source of the signal supplied to the input terminal 40, and 45 is a resistor as an internal resistance of the signal source 44, which are connected in series between the input terminal 40 and the ground. Ru.

Further, 46 is a load resistor, which is connected between the output terminal 41 and ground.

FIG. 9 shows an example in which the present invention is applied to a variable tuning circuit. In this case, a transistor 3, a coil 4, a variable resistor 5,
An active inductance circuit consisting of a power supply 6 is connected to a capacitor 4.
7 in parallel to form a tuned resonant circuit.

As in the case of FIG. 8, a voltage source 44 that supplies an input voltage between the input terminal 40 and the ground and a resistor 45 serving as its internal resistance are connected in series.

Here, if the capacitance value of the capacitor 47, the reactance value of the C1 coil 4, and the voltage amplification degree of the L1 inductance increasing circuit are AV, then the cutoff frequency is f.

can be expressed by the following equation 01).

Next, an example in which the present invention is applied to a variable oscillation circuit will be explained with reference to FIG.

This example is the case of a Colpitts oscillator circuit.

50 is a transistor for oscillation, and 51 is a power supply for bias supply, the positive terminal of which is connected to the collector of transistor 50, and the negative terminal thereof is grounded.

Further, resistors 52 and 53 connected in series are connected in parallel to the power supply 51, and the midpoint of the connection is connected to the transistor 5.
0, thereby providing a fixed bias to the base of transistor 50.

The collector of transistor 50 is grounded via capacitor 55, and its emitter is grounded via resistor 54.

Further, the emitter of the transistor 50 is connected to the midpoint of the capacitors 56 and 57 connected in series, and the emitter of the transistor 50 is
The other end of 6 is connected to the gate of field effect transistor 3 of the inductance increasing circuit (this capacitor 58
connected to the base of the oscillation transistor 50 via
The other end of capacitor 57 is grounded.

That is, in this case, the coil of the Colpitts oscillation circuit is replaced with an active inductance circuit 13, and by adjusting the variable resistor 5, the oscillation frequency can be easily varied.

Thus, according to the active inductance circuit of the present invention, an active element such as a field effect transistor or a bipolar transistor is provided, and a coil is connected between the input electrode and the output electrode of the active element. Since a resistor is connected between the output electrode and the ground, the apparent inductance can be reduced to, for example, 1 with a very simple circuit configuration.
When the coil is mounted on a printed circuit board, etc., even if the coil has a large inductance value, its size can be substantially reduced to an extremely small value, so that other electronic It can be arranged in high density with other parts.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the basic principle of the active inductance circuit of the present invention, Figures 2, 3 and 4 are equivalent circuit diagrams of Figure 1, and Figures 5 to 10 are circuit diagrams showing the basic principle of the active inductance circuit of the present invention. It is a circuit diagram of an example. 3.9 is an active element, 4 is a coil, and 5 is a resistor.

Claims (1)

[Scope of utility model registration request] a transistor, a coil connected between a gate (base) electrode and a source (emitter) electrode of the transistor, and a resistor connected between the source (emitter) electrode of the transistor and a reference potential point; An active inductance circuit comprising a voltage source connected between the drain (collector) electrode of the transistor and a reference potential point.