JPS5949722B2 - active load circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is useful for signal sources requiring matched load resistances (e.g. M
The present invention relates to an active load circuit whose purpose is to reduce noise generated from a matched load resistor in an amplifier circuit that inputs an M-type pickup cartridge.

FIG. 1 shows a conventionally used RIAA equalizer amplifier for MM type pickup cartridges.

In Fig. 1, 1 is an MM type pickup cartridge including components of inductance 2 and resistance 3, and 4 is an output terminal of cartridge 1 (input terminal of an equalizer amplifier).
, 5 is a matching load resistor, 6 is an amplifier, 7 and 8 are inverse RIAA
A feedback circuit with characteristics, 9 is an output terminal of an equalizer amplifier.

In the case of a normal MM type pickup cartridge, the inductance component 2 is about 500 mH, the resistance component 3 is about IKΩ, and the matching load resistance 5 is about 47Ω.

In the circuit shown in Fig. 1, if we pay attention to the noise excluding the noise generated from the amplifier 6 and the feedback circuit 7.8, when the cartridge 1 is installed, the low-frequency noise is almost only the noise generated from the resistor component 3. However, as the frequency becomes higher, the contribution rate of the noise generated from the matched load resistor 5 increases, and around 1QKHz, most of the noise is generated from the matched load resistor 5.

Further, the noise generated when the cartridge 1 is removed is the noise itself generated from the matching load resistor 5.

By the way, the value of this matching load resistor 5 is usually specified on the MM type cartridge side, and changing the value of this load resistor 5 changes the frequency characteristics, so it is not possible to remove it or change its value significantly. is not allowed.

However, when the matched load resistor 5 is connected, the high-frequency noise when the cartridge 1 is installed and the noise when the input is open are determined by the matched load resistor 5.
The problem is that no matter how much noise is suppressed on the amplifier side, the overall noise cannot be reduced below that level.

The present invention provides an active load circuit that solves these problems.

Embodiments of the present invention will be described below with reference to FIGS. 2 to 16.

FIG. 2 is a circuit diagram for explaining the present invention in detail,
3 to 15 are circuit diagrams of specific embodiments.

In FIGS. 2 to 15, 1 to 9 correspond to the same numbers in FIG. 1, and 10 corresponds to the terminals 11, 12,
13 is a current conversion means, 14 is a converted load resistance,
15 is a positive side power supply, 16 is a transistor, 17 is a transistor, 18 is a diode, 19.20 is a resistor, 21 is a transistor, 22 to 30 are transistors connected in parallel, 31.32 is a transistor, 33.34 is a coupling capacitor , 35.36 is a DC current source, 37 is a negative side power supply, 38
is a coupling capacitor, 39 is a DC current source, 40 is a FET,
41 to 49 are FETs connected in parallel, 50 and 51 are FEs
It is T.

First, the principle of the present invention will be explained with reference to FIG.

In FIG. 2, the current conversion means 10 has a voltage at the terminal 11 and a voltage at the terminal 12 that follow each other (that is, an AC voltage gain from the terminal 11 to the terminal 12, and an AC voltage gain from the terminal 12 to the terminal 11). The AC voltage gain from terminal 12 is divided into terminal 11 and terminal 13, and the current gain from terminal 11 to terminal 12 is l/n.
This is a circuit or element in which the current gain from terminal 12 to terminal 11 is n times.

Also, the value of the resistor 14 is R
When it is L, it is 1/nRL.

Now, when a V signal is applied to terminal 11, V is applied to terminal 12.
A voltage appears, and the current at terminal 12 is /RL.

becomes.

At this time, since the current at the terminal 11 is 1/n of the current at the terminal 12, it becomes v/RL.

Therefore, the resistance value when looking into terminal 11 from terminal 4 is RL, which is equal to that in the case of FIG.

Next, the noise voltage generated from the resistor 14 is V.

Then, V n "!■" becomes.

(However, k is the Boltzmann constant, T is the absolute temperature, and Δf is the noise bandwidth.

) Since the voltage gain from terminal 12 to terminal 11 is 1,
Assuming that the input impedance of the amplifier 6 is sufficiently high, the noise voltage Sn2 appearing at the terminal 4 when the cartridge 1 is opened is Vn2 =Vn=W.

The value of this is the noise voltage generated from resistor 5 in Figure 1.
n1 = Buddha 4 〒AfRt decreases to J.

In this way, instead of the load resistor 5 shown in FIG. 1, the current converting means 10 and the converted load resistor 14 shown in FIG.
By using an active load circuit composed of, the effective load resistance value is equivalent to the matched load resistance 5,
As for the noise voltage, the lifetime of the matching load resistor 5 can be reduced.

FIG. 3 uses a transistor 16 as the current conversion means, and is intended to explain the operating principle of the current conversion means of the present invention more clearly.

In the case of FIG. 3, the value of the resistor 14 may be RL/hFE with respect to hFE of the transistor 6.

In this case, the noise voltage of the active load circuit is 4- becomes.

In Figure 3, a transistor is used as the current conversion means, but normally the hFE of the transistor varies widely,
Furthermore, since the voltage changes depending on the temperature, it is effective to use a constant hFE transistor instead of a normal transistor.

Figure 4 shows a transistor '17 as a current conversion means.
, a current amplifier composed of a diode 18 and resistors 19 and 20.

In the case of the current amplifier shown in Figure 4, the current gain is approximately 19
Since it can be approximated by a ratio of .degree. 20, the variation in current amplification factor and temperature change are smaller than in the case of FIG. 3, and therefore the variation in effective resistance value as an active load circuit and temperature change can be reduced.

Furthermore, since the base circuit of the transistor 17 is shunted by a series circuit of a diode 18 and resistors 19 and 20, the shock noise caused by the base current is
It has the advantage of being smaller than the case shown in the figure.

FIG. 5 shows a transistor 21 whose base and core are connected (diode-connected) and nine transistor groups 22 to 30 connected in parallel as current conversion means.
This uses a current shunt circuit configured with.

The value of the resistor 14 is 1/10RL.

In the current shunting circuit shown in FIG. 5, the current of the resistor 14 is shunted to each transistor 21 to 30 by exactly 1710, so the current gain n as a current conversion means is exactly 10, and there is no variation or change due to temperature. .

Therefore, variations in effective resistance value as an active load circuit and changes due to temperature are eliminated.

Furthermore, since the base circuits of the transistors 22 to 30 are directly shunted by the diode-connected transistor 21 (without using a resistor), the shot noise caused by the base current of the transistors 22 to 30 is It's even smaller than that.

In the case of FIG. 5, the noise voltage generated from the active load circuit is q of the noise voltage from the matching load resistor unit 5.

In FIG. 6, the bases of transistors 22 to 30 in FIG. 5 are connected to the feedback input terminal of an amplifier 6. In FIG.

In FIG. 6, when the gain of amplifier 6 is sufficiently large,
Since the voltage at the feedback input terminal follows the voltage at terminal 4, the operation is similar to that shown in FIG.

However, the case of FIG. 6 is advantageous compared to the case of FIG. 5 because the error is reduced because the base currents of the transistors 22 to 300 do not flow toward the terminal 4.

In FIG. 7, the base of the transistor 21 is also connected to the amplifier 6.
The operation is as shown in Figures 5 and 6.
This is the same as the case shown in the figure.

If the gain of the amplifier 6 is not sufficient, the error voltage between the terminal 4 and the feedback input terminal of the amplifier 6 will increase. will be more advantageous.

In the case of FIGS. 5 to 7, one transistor and nine transistors 22 connected in parallel are used as the current conversion means.
30, but instead of these nine parallel connected transistors 22 to 30, one transistor whose base-emitter junction surface type is 9 times that of transistor 21 is used. A similar effect can be obtained.

In FIG. 8, a transistor 31 and a transistor 32 whose bases and collectors are connected are used as current conversion means, and the bases of the transistors 31 and 32 are connected to the terminal 4, and the emitters are connected through coupling capacitors 33 and 34. The emitter current of the transistor 31 is supplied from a DC current source 35, and the emitter current of the transistor 31 is connected to the converted load resistor 14.
The emitter current of 2 is supplied from the DC current source 36, and by setting the current ratio of the DC current sources 35 and 36 to 1:9, the current of the resistor 14 is converted to 1/10 and supplied to the terminal 4. This is what I did.

Generally, the base-emitter resistance re of a transistor is re=26 mV/Ie (1, emitter current), and is inversely proportional to the emitter current.

Therefore, the alternating current applied to the emitters of transistors connected in parallel with each other is proportionally distributed according to the emitter current of the respective transistor.

In the case of Figure 8, the noise voltage of the active load circuit is
As in the case of Fig. 7, he becomes a subordinate of Low Motion 5.

FIG. 9 shows the base of the transistor 32 in FIG.
It is connected to the feedback input terminal of the amplifier 6.

In FIG. 10, the bases of the transistors 31 and 32 in FIG. 8 are connected to the feedback input terminal of the amplifier 6.

In FIG. 11, the DC current source for the transistor 31 in FIG. 8 is supplied from the collector side.

In FIG. 12, the emitter and base-collector of the transistor 31 in FIG. 11 are exchanged so that a DC current source is supplied from the emitter side.

In FIG. 13, the base of the transistor 32 in FIG. 11 is connected to the feedback input terminal of the amplifier 6.

FIG. 14 shows the case of FIG. 12 in which the base of the transistor 32 is connected to the feedback input terminal of the amplifier 6.

Figures 8, 9, 11, 12, 13, 14
In the figure, a similar effect can be obtained by using a diode instead of the transistor 31 whose base and collector are connected.

In FIG. 15, the transistors 21-30 in FIG. 5 are replaced with FETs 40-49.

In FIG. 16, the transistors 31 and 32 in FIG. 8 are replaced with FETs 50 and 51.

The one using the FET shown in Figs. 15 and 16 is
The operation is similar to that shown in FIGS. 5 and 8 using transistors, but the error is reduced because there is no base current.

As described above, according to the present invention, (1) the generated noise is reduced by ÷(
n is the current conversion ratio).

(2) The resistance value seen from the signal source is the same value as the matching load resistance value.

(3) Since the current conversion means is composed of the first and second active elements, the current shunting ratio can be determined accurately, and as a result, a more accurate matched load resistance value can be obtained.

This excellent effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional equalizer amplifier, FIGS. 2 and 3 are diagrams for explaining the present invention in detail, and FIGS.
16 are circuit diagrams each showing an embodiment of the present invention. 1...Pickup cartridge, 5...
...Matched load resistance, 6...Amplifier, 7,8...
... Feedback circuit, 10 ... Current conversion means, 1
1...First terminal, 12...Second terminal, 13...Third terminal, 14...Converted resistance.

Claims (1)

[Claims] 1 comprises at least a first, second and third terminal, the voltage of the first terminal and the voltage of the second terminal follow each other, and the current of the second terminal flows to the first terminal and the third terminal; A current converting means that divides the current so that the current at the first terminal is smaller than the current at the second terminal, and a resistor whose one end is connected to the second terminal of the current converting means. , the first terminal of the current converting means and the other end of the resistor are connected to a potential point following the input and the cold side of the amplifier, respectively, and the current converting means is connected to the first terminal of the current converting means. , first and second active elements having fourth, fifth and sixth terminals having substantially the same relationship as the second and third terminals; A fourth terminal of the active element is connected to the first terminal of the current converting means, a fifth terminal of the first and second active elements is connected to the second terminal of the current converting means, and the First,
The sixth terminal of the second active element is connected to the third terminal of the current converting means.
An active load circuit characterized in that it is connected to the terminals of.