JPS6023523B2 - Grounded emitter transistor amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a common emitter transistor amplifier,
An object of the present invention is to provide a common emitter type transistor amplifier in an M tuner that can prevent an extreme drop in detection output even under extremely strong human power.

Referring to the drawings below, FIG. 1 shows a circuit diagram of an example of a secondary common emitter type transistor amplifier.

In the figure, reference numeral 1 denotes a signal source, one end of which is connected, and the other end of which is connected to the base of an NPN transistor 3 via a capacitor 2. The emitter of the transistor 3 is followed via a resistor 4 and the collector is connected via a resistor 5 to a power supply terminal 8 while directly connected to an output terminal 9. Further, a bias voltage is supplied to the base of the transistor 3 from a bias power supply terminal 7 via a resistor 6. The conventional emitter-grounded transistor amplifier shown in FIG. An output signal is obtained. As is well known, in an AM tuner, the components in the RF amplified output signal of the RF amplifier are fed back to the RF amplifier as an AGC voltage via the frequency mixing stage, intermediate frequency amplifier, and AGC detection/filter circuit in the AM tuner, and the R
The amplitude of the AM component in the F amplified output signal is maintained approximately constant. Therefore, when a super strong input RF signal (that is, an RF signal having an extremely strong amplitude) as shown in FIG. 2A is applied from the antenna circuit as the signal source 1 to the base of the transistor 3, the super strong input During the positive half-cycle of the RF signal, transistor 3 is driven into the saturation region, and during the negative half-cycle of this very strong input RF signal, transistor 3 is driven into the cut-off region.

In the RF signal of FIG. 2A, the envelope static 2,...
are the AM components of the RF signal, and the high frequency agent 23 is the high frequency carrier wave component of the RF signal. When transistor 3 is driven into the saturation region during the positive half cycle of a very strong input RF signal, not only the PN junction between the base and emitter of transistor 3 is forward biased, but also the PN junction between its collector and base is The PN junction is also forward biased.

Therefore, between the collector and emitter of transistor 3, the forward fin pressures of the two PN junctions cancel each other out, so that, as is well known, the collector and emitter of transistor 3 in the saturation region cancel each other out.
The emitter voltage has an extremely small value that can be ignored. If the emitter resistor 4 has a value that can be ignored compared to the collector resistor 5, the voltage drop across the emitter resistor 4 in this case also has a value that can be ignored. Therefore, when the transistor 3 is driven into the saturation region during the positive half cycle period of the super strong input RF signal, the emitter voltage (ie, the ground voltage of zero volts) appears as the collector output voltage from the output terminal 9.

On the other hand, when the transistor 3 is driven to the cutoff region during the negative half cycle period of the super strong input RF signal, the fin source voltage Vcc of the power supply terminal 8 appears as the collector output voltage from the output terminal 9.

FIG. 2B shows the output waveform at the collector output terminal 9 of the transistor 3, which is alternately driven into the saturation region and the cutoff region by a super strong input RF signal.
The envelope parts b, b2 corresponding to the AM component disappear, and only a pulse waveform that is synchronized with the high frequency carrier wave of the RF signal and changes between the power supply voltage Vcc and the ground voltage GND is obtained. Therefore, as shown in Figure 2B, if the RF output signal of the pulse waveform with the envelope quiet and the pulse waveform b2 disappeared is obtained from the output terminal of the RF amplifier, it is natural that the output of the intermediate frequency amplifier in the AM tuner is Envelope 0 or Q from the output of the AM detector connected to
Not only will it be impossible to obtain audio detection output corresponding to
The following malfunctions occur in connection with the GC operation. In other words, when the RF output signal of the RF amplifier contains envelopes q and b2 as shown in FIG. 2B and becomes a clipped pulse output, the intermediate frequency amplifier's extended output signal similarly becomes a clipped state that does not include an envelope. The pulse waveform is as follows.

The AGC detection/filter circuit connected to the output of the intermediate frequency amplifier half-wave rectifies and smoothes the output signal of the intermediate frequency amplifier to generate an AGC voltage corresponding to the envelope as an AM component with the high frequency carrier component removed. However, if the IF output signal of the intermediate frequency amplifier is a clipped pulse waveform that does not include an envelope, the AGC voltage obtained from AGC detection and filtering will be at a relatively low level. Therefore, as a result of gain control using this low-level AGC voltage, the RF amplifier of the AM tuner amplifies the ultra-strong input RF signal with a large amplification factor, so the RF
The output clip state of the amplifier is further exacerbated, resulting in a malfunction called the so-called AGC lockout phenomenon. The present invention eliminates such conventional drawbacks,
Examples thereof will be described in detail below.

3 and 4 are a vertical cross-sectional structural diagram and a circuit diagram, respectively, of an embodiment of a common emitter transistor amplifier according to the present invention.

Such an emitter-grounded transistor amplifier is suitable for use as an RF amplifier in an AM tuner, and as is well known, the AM component in the RF amplified output signal is processed by a well-known mixing stage, an intermediate frequency amplifier, and an AGC detection/filter circuit. The signal is fed back to the RF amplifier as an AGC voltage via the AGC voltage, and an audio detection output is obtained from the output of the AM detector connected to the output of the intermediate frequency amplifier. In the figure, 11 is a P-type semiconductor substrate,
N-type epitaxial growth layers 12 to 14 are formed thereon. Next, P+ type separation layers 15 to 18 are formed, as well as a P type base diffusion layer 19 for forming an NPN transistor 24, a P type resistance diffusion layer 20 for forming a damping resistor 25, and a resistance of a pinch resistor 26. A P-type resistance diffusion layer 21 for forming a layer 26a is formed. Next, an N-type emitter diffusion layer 22 for forming the transistor 24 and an N-type cathode diffusion layer 23 for forming the diode 26b of the pinch resistor 26 are formed. Next, the P-type substrate 11 is grounded, and the emitter diffusion layer 22 of the transistor 24 is connected to the resistor 2.
7 to ground, and the epitaxial growth layer 12 forming the collector of the transistor 24 is connected to the output terminal 301 as well as to the power supply terminal 32 via the resistor 31.
Further, the base diffusion layer 19 of the transistor 24 and one end of the resistance diffusion layer 20 of the damping resistor 25 are connected. Next, the other end of the resistance diffusion layer 20 and one end of the resistance diffusion layer 21 of the pinch resistor 26 are connected. Further, the N-type epitaxial growth layers 13 and 14 are connected to the power supply connection terminal 33.
Next, the other end of the resistance diffusion layer 21 and the cathode diffusion layer 23 are connected to the power supply terminal 34. In this state, terminals 32, 3
3 and 34, and connect the capacitor 2 to the base diffusion layer 19 of the NPN transistor 24.
9 from the signal source 28, as indicated by a in FIG. 2A.
Supply M signal. Here, since the N-type diffusion layer 23 is reverse biased with respect to the P-type diffusion layer 21, the N-type diffusion layer 23
The P-type layer 21 directly under the region 3 is controlled by the depletion layer extending from the N-type layer 23, and becomes a relatively high resistance region 26a, that is, a pinch resistance region. Furthermore, the P type layer 21 and the N
A PN junction diode 26b between the mold layer 23 and the pinch resistor 26a is connected in parallel. In the emitter grounded transistor amplifier configured in this manner, when the input amplitude voltage of the signal source 28 is small, the diode 26 maintains a non-conducting state. Although the power supply internal impedance of the bias voltage source (not shown) connected to the terminal 34 is generally a small value of 4, the resistance value of the resistance region 26a of the pinch resistor 26 is extremely high, so that the emitter The input impedance when looking at the bias voltage source terminal 34 from the base of the grounded transistor 24 can be set to a high value. Therefore, when the input amplitude voltage of the signal source 28 is small, the envelope component corresponding to the AM component can be extracted without clipping occurring at the output terminal of the collector output terminal 30.

Therefore, a case will now be considered in which a super strong input AM/RF signal is applied to the base of the transistor 24 from the signal source 28.

During the negative half-cycle period of the ultra-strong input AM/RF signal, the diode 26b connected in parallel to the high-resistance resistor 26a is non-conducting, so the voltage waveform at the base of the transistor 24 becomes waveform C in FIG. 2C. As shown, it almost matches the signal waveform Co of the signal source 28.

Assuming that the bias voltage applied to the terminal 34 is VB and the forward voltage of the diode 26b is VF, when a positive half cycle of an ultra-strong input AM/RF signal exceeding the level of VB + VF is applied, a high resistance value will occur. A diode 26b connected in parallel with the resistor 26a is suitable.

At this time, the voltage waveform at the base of the transistor 24 does not directly follow the signal waveform at the signal source 28 to a high level as shown in FIG.
As a result of the conducting operation (limiter operation) of b, the signal source 28
A compressed voltage waveform C2 of that amplitude level is applied to the base of the transistor 24 by the signal source impedance (not shown) of the diving resistor 25 and the internal impedance of the bias voltage source (not shown) connected to the terminal 34. become what is done. The base voltage waveform C2 of the transistor 24 compressed in this manner has a compressed envelope portion C4 corresponding to the envelope portion C3 of the signal waveform Co of the signal source 28. Furthermore, since the positive half cycle C2 of the base voltage waveform of transistor 24 is compressed in this manner, transistor 24 is prevented from being driven to full saturation. Figure 2 D is
3 shows an output waveform D3 at the collector output terminal 30 of the grounded-emitter transistor amplifier according to the present invention.

An uncompressed large amplitude negative half-cycle signal applied to the base of transistor 24 drives transistor 24 into the cut-off region and its collector output voltage rises to the power supply voltage Vcc at power supply terminal 32. Therefore, a high level clip of the collector output voltage occurs and the high level envelope portion D, disappears. On the other hand, according to this embodiment, by applying the compressed positive half-cycle signal C2 to the base of the transistor 24, the transistor is prevented from being driven into the saturation region, and its collector output voltage is grounded. The compressed base voltage waveform has an envelope D2 corresponding to the envelope C4 of 2 and changes between the intermediate voltage level VM and the ground voltage GND without decreasing to the voltage level VM. Therefore,
By using the above-mentioned common emitter type transistor amplifier for the RF amplifier of the AM tuner,
A proportional to the compressed envelope portion D2 corresponding to the M component
Since the GC voltage and the audio detection output are obtained from the AGC detection/filter circuit and the A-shape detector, the above-mentioned undesirable AGC lockout phenomenon and audio detection output loss phenomenon can be prevented.

When the emitter-grounded transistor amplifier of the present invention is applied to an RF amplifier in an AM tuner, it will be practical for the amplifier even if the electric field strength near the transmitting station antenna in AM broadcasting is about 14 years ago/m. Therefore, it is possible to prevent an extreme drop in the detection output.

In the above embodiment, the pinch resistor 26 and its parasitic diode 26b are used, but a diode may be connected to the linear resistor in the integrated circuit and a bias power supply V may be supplied to this diode.

The present invention can also be applied to a bias circuit for a PNP transistor, in which case a parasitic diode of a pinch resistor is followed in the opposite direction.

Further, in the present invention, it goes without saying that the damping resistor 25 can be omitted if the internal impedance of the bias voltage source connected to the terminal 34 is large.

As described above, according to the embodiment of the present invention, the bias voltage is supplied to the base of the emitter-grounded amplification transistor via the pinch resistor and the damping resistor in sequence, and the resistor of the pinch resistor and the parasitic diode are connected in parallel. A circuit is used to perform a limiter operation on the input waveform on one side, the damping resistor weakens the limiter effect, and the transistor is operated in the active region without being completely saturated, and the input waveform on the other side is On the other hand, since the above-mentioned transistor is cut off, it has the advantage of preventing an extreme drop in the detection output even when an AM tuner receives an extremely strong input.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an example of a conventional bias circuit, Figure 2A
D to D are AM input/output signal waveform diagrams of emitter-grounded transistor amplifiers using the bias circuit of the present invention, and FIGS. 3 and 4 respectively show emitter-grounded transistor amplifiers using the bias circuit of the present invention. FIG. 2 is a longitudinal cross-sectional structural diagram and a circuit diagram of one embodiment of the present invention. 1, 28... Signal source, 2, 29... Capacitor, 3, 2
4...Transistor, 4,5,6...Resistance value, 7,8,
32, 34... Power supply terminal, 9, 30... Output terminal, 25... Damping resistor, 26... Pinch resistor, 26b... Parasitic diode. Figure 3 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. A signal source 28, a common emitter transistor 24 whose base is connected to the signal source, and a resistor 26a connected between the base of the common emitter transistor and a bias voltage source. A common emitter type transistor amplifier comprising: a diode 2 connected to the resistor 26a;
6b are connected in parallel, and when the signal source 28 generates a signal with a large amplitude level, the diode 26b becomes conductive to prevent saturation of the grounded emitter transistor 24. amplifier. 2. A signal source 28, a common emitter transistor 24 whose base is connected to the signal source, and a resistor 26a and a diode 26b connected in parallel between the base of the common emitter transistor and a bias voltage source. When the signal source 28 generates a signal with a large amplitude level, the diode 26b becomes conductive to prevent saturation of the transistor 24 and generate an AM component corresponding to the AM component of the signal from the signal source 28. is the above transistor 2
4. A common emitter type transistor amplifier characterized in that the transistor amplifier is prevented from disappearing at the collector output terminal 30 of No. 4. 3. A signal source 28, a common emitter transistor 24 whose base is connected to the signal source, and a resistor 26a and a diode 26b connected in parallel between the base of the common emitter transistor and a bias voltage source. When the signal source 28 generates a signal with a large amplitude level, the diode 26b becomes conductive, thereby preventing saturation of the transistor 24 and generating an AM component corresponding to the AM component of the signal from the front signal source 28. is the transistor 24
The resistor 26a is formed by the P-type resistance layer 21 of the pinch resistor 26, and the diode 26b is formed by the P-type resistor layer 21 of the pinch resistor 26.
1. A common emitter type transistor amplifier characterized in that it is formed by a parasitic PN junction between a type resistor layer 21 and an N type cathode layer 23.