JPS6051804B2 - amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that improves interference signal removal in an equalizer circuit for an audio preamplifier.

A conventional equalizer circuit is shown in FIG.

In Fig. 1, the input signal is transferred from input terminal 1 to capacitance A [3
・、・IJ−＾ −、ι・Λ、・・・、1・1 rate、
It is applied to 1', ni-n 1, ノ, 05.-;-rel--ノ', ゛,,-.

Here, the base of the transistor 6 is grounded through a capacitor 4 and a resistor 5, the emitter is connected to a positive power supply 14 through a resistor 7, and the collector is connected to a negative power supply 15 through a load resistor 8. A first amplifier circuit is constituted, and its output is connected to the base of a second amplifier circuit constituted by a transistor 10 and a load resistor 9. The output of the second amplifier circuit is supplied to an emitter follower circuit composed of a transistor 11 and a resistor 12, and the emitter of the transistor 11 is connected to an output terminal 22 via a capacitor 13.

The output of the transistor 11 is capacitance 18, 19, resistance 20,
21, a resistor 16, and a capacitor 17, a feedback circuit for determining the RIAA characteristics provides feedback to the emitter of the transistor 6.

In such an equalizer circuit, the signal-to-noise ratio (hereinafter S/N
In order to improve this, it is natural to use a low-noise element for the first stage transistor 6, but it is also necessary to reduce the thermal noise of the base J resistor 3 inserted for the purpose of preventing oscillation. . However, if an unnecessary high-frequency interference signal from a transceiver, amateur radio, pager, etc. is supplied to input terminal 1, and the value of resistor 3 is small, the low-frequency leaker consisting of base resistor 3 and capacitor 4 will As the output power off frequency becomes higher, the unnecessary signal is supplied to the first stage transistor 6 without being attenuated, the peak is detected at the P-N junction of this first stage transistor, and the signal is amplified and outputted to the output terminal 22. Conventionally, since the resistor 3 was large and the cutoff frequency of the low frequency leaker constituted by the parallel capacitor 4 was low, it was at an acceptable level against this type of interference.

However, when trying to improve the S/N from the conventional circuit, the resistor 3
The value of must be made small, resulting in a problem of poor unnecessary signal removal rate.

In the present invention, an inductance is inserted between the emitter of the first stage transistor and the feedback circuit that determines the RIAA characteristics, and the impedance is high against high frequency interference signals, and the amplification degree of the first stage transistor is extremely small to attenuate unnecessary signals. , and by adding an inductance to the input, S
The present invention provides an amplifier circuit that forms a low-frequency leaker with an inductance and an input parallel capacitance without degrading /N, and attenuates unnecessary interference signals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An amplifier circuit according to the present invention will be explained below with reference to embodiments shown in the drawings.

Examples of the present invention are shown in FIGS. 2, 3, 4, and 5.

In FIG. 2, an input signal is applied from an input terminal 1 to the base of a first stage transistor 6 via a capacitor 2 and a resistor 3. Here, the base of the transistor 6 is grounded through a capacitive male resistor 5, and the emitter is connected to the positive power supply 1 through a resistor 7.
4, and its collector is connected to a negative power supply 15 via a load resistor 8 to constitute a first amplifier circuit, the output of which is composed of a transistor 10 and a load resistor 9. is supplied to the base of the second amplifier circuit. The output of the second amplifier circuit is supplied to an emitter follower circuit composed of a transistor 11 and a resistor 12, and the emitter of the transistor 11 is connected to an output terminal 22 via a capacitor 13. The output of transistor 11 is capacitance 18, 19, resistance 20, 21
It is supplied to the emitter of the transistor 6 through a feedback circuit that determines the RIAA characteristics, which is composed of a resistor 16 and a capacitor 17, and an inductance 23 connected in series with the feedback circuit to provide negative feedback. In Fig. 2, when an unnecessary high-frequency interference signal is input to the input terminal 1, the base resistor 3 and the capacitor 4 are In the low-frequency leaker composed of the above, unnecessary signals are input to the first stage transistor 6 without being attenuated.
However, since the inductance 23 is included in the emitter of the first-stage transistor 6, the gain of the transistor 6 becomes extremely large for high frequencies, and the impedance of the inductance 23 becomes extremely large, resulting in extreme attenuation, and unnecessary high-frequency interference signals are not amplified. First, the unnecessary output appearing at the output terminal 22 is reduced. In FIG. 3, a) inductance 25 is inserted in place of the resistor 3 in FIG. 2 for the purpose of lowering the level of the interference signal input to the transistor 6. In this circuit, an unnecessary high-frequency interference signal that enters the input terminal 1 is attenuated by a low-frequency leaker composed of an inductance 25 and a capacitor 4, and is input to the transistor 6.

Furthermore, as explained in the embodiment of FIG.
Since the emitter of has an inductance 23,
The amplification of high frequencies is extremely reduced. In this way, two-fold countermeasures are taken against interference signals of high frequencies. However, in the embodiments shown in Figures 2 and 3 above, if the input terminal 1 is short-circuited, the inductance and input capacitance form a resonant circuit, and if the figure of merit Q of the inductance is high, oscillation occurs. . The embodiments shown in FIGS. 4 and 5 solve this problem. 4 and 5 have the same structure, operation, and effect as the embodiments in FIGS. 2 and 3, respectively, but the difference is that the inductances 23 and 2 are the same.
In this circuit, resistances 24 and 26 are added in parallel to 5, each having a value that does not lose the effect of the inductance in the relevant interference frequency band, and the figure of merit Q of the inductances 23 and 25 is dumped to increase stability. . Although the present invention has been described using a three-stage amplifier using transistors, FETs or the like may also be used, and it goes without saying that the number of stages of the amplifier is not limited.

The effects of the present invention are shown in FIG.

Figure 6 shows a frequency of 10 MHz, a modulation depth of 30%, and a modulation frequency of 1.
KHz (7), the detection output level appearing at the output terminal 22 when an AM signal is input to the input terminal 1 as an unnecessary interference signal is measured, and the curve 30 shows the characteristics of the conventional amplifier circuit.
Curve 31 is the characteristic of the amplifier circuit according to the present invention. As can be seen from the measurement results, the amplifier circuit according to the present invention has an improvement of about 20 c1B or more compared to the conventional one, and is therefore very effective.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional amplifier circuit, Figures 2, 3, 4, and 5 are circuit diagrams of an amplifier circuit according to the present invention, and Figure 6 is an input/output characteristic of an amplifier circuit according to the present invention. It is a diagram. 1... Input terminal, 6... First stage transistor, 20,
21... Feedback resistance, 19, 18... Feedback capacitance, 23
・Inductance.

Claims (1)

[Claims] 1. An emitter-grounded first-stage transistor to which an input signal is supplied to the base and an output signal is taken out from the collector;
An amplifier comprising: an emitter follower type final stage transistor connected in cascade to the first stage transistor; and a negative feedback circuit that supplies a negative feedback signal from the emitter of the final stage transistor to the emitter of the first stage transistor through a feedback circuit exhibiting RIAA characteristics. In the circuit, the value of the resistor connected in series between the base of the first stage transistor and the input terminal is set to such a value that its thermal noise can be ignored, and the negative feedback circuit is connected between the negative feedback circuit and the emitter of the first stage transistor. An equalizer amplifier circuit characterized in that an inductance is connected that has negligible impedance for signals in a frequency band affected by the amplitude frequency characteristics of the circuit and has a large impedance for signals of frequencies higher than the frequency band.