JPS5811059Y2 - transistor amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor amplifier including two transistors.

Standard signal generators require wideband, large signal, and low distortion transistor amplifiers.

FIG. 1 shows a conventional transistor amplifier.

The base of the transistor 2 is a signal source 4 with an internal resistance 6
, its emitter is connected to a reference voltage source or ground through an emitter resistor 8, and its collector is connected to ground through a load resistor 10.

It should be noted that the biasing means are not shown.

Such transistor amplifiers are single transistor current negative feedback amplifiers.

If the resistance value of the external emitter resistor 8 is higher than the intrinsic emitter resistance re of the transistor 2, the emitter voltage follows the base voltage very precisely.

However, in a large amplitude amplifier such as an output stage amplifier, the emitter voltage cannot follow the base voltage because the external emitter resistance 8 is low.

Also, as at low frequencies, if the current amplification rate β is high <
, 1b (if IC, collector and emitter current IC
and ie are approximately equal, and the load voltage follows the emitter voltage or input signal.

In a range where the current amplification rate β is high (for example, 100 or more), even if the current amplification rate β is dependent on the collector current, it is still
, < lc, the nonlinearity of the current amplification factor β has little effect on the overall linearity of the amplifier.

However, at frequencies above the emitter cutoff frequency fαe (=fT/β, where f is the gain band peak), the current amplification rate β decreases, so its nonlinearity causes the following two effects.

The first effect is the nonlinearity between collector current and emitter voltage.

The second effect is that if the signal source is not a pure voltage source (zero internal impedance), the input impedance of the transistor changes with β of the transistor, resulting in modulation of the signal source voltage.

Therefore, an object of the present invention is to improve the above-mentioned drawbacks of the prior art and to provide a transistor amplifier that has good linearity over a wide range of oil frequencies.

The details will be explained below with reference to FIG. 2, which shows a preferred embodiment of the present invention.

A signal voltage source 12 with an internal resistance 14 is connected to the base of the first transistor 18 via a coupling capacitor 16, and a bias voltage VB is applied to the base of the transistor 18 via a bias resistor 20.

A decoupling capacitor 22 is inserted between the bias voltage VB and a reference voltage or ground.

The emitter of the first transistor 18 is connected to ground through the first resistor 24 and to the base of the second transistor 26, and the emitter of the second transistor 26 is connected to the ground through the first resistor 24.
8 to ground.

Note that the resistance of first resistor 24 is approximately equal to the resistance of second resistor 28.

The collectors of the first and second transistors 18 and 26 are connected to a common load.

One end of load resistor 32 is grounded, and the other end is connected to the collectors of transistors 18 and 26 via capacitor 30.

Collector voltage V. is applied to the collectors of transistors 18 and 26 via inductor 34.

Although the DC resistance of the inductor 34 is low, the AC impedance at the operating frequency is sufficiently higher than the load resistance.

The transistor amplifier of the present invention is divided into two stages and connected in a quasi-Darlington connection, but it differs from conventional Darlington amplifiers in that each stage is configured to operate at approximately the same current level. differ.

In other words, the base of second transistor 26 receives approximately the same input signal voltage as first transistor 18, and transistors 18 and 26 drive a common load.

If the same gain as the conventional amplifier shown in FIG. 1 is desired, the values of resistors 24 and 28 can be twice the value of resistor 8 for the same load.

(2Rs = R24 = R28). Therefore, the negative feedback by the first stage emitter resistor 24 is doubled and the input impedance increases, so the change in input impedance due to the change in β is absorbed by the fixed bias resistor 20.
Modulation of the signal source voltage is less than in the prior art.

Furthermore, since the transistor 26 receives the input signal from the emitter of the transistor 18, which has a low output impedance,
There is even less modulation of the signal source voltage to transistor 26.

Furthermore, by housing both transistors 18, 26 in a common housing, such as a TO-117, so that their junction temperatures are approximately equal, the operating current levels of both transistors can be more accurately matched.

If a non-linear base current of transistor 26 is provided by transistor 18, ie, if the base current increases (or decreases), then the emitter and base voltages of transistor 26 increase (or decrease) and transistor 18 The base-emitter bias voltage of is decreased (or increased).

Therefore, increasing (or decreasing) transistor 26
The collector current is offset by the decreasing (or increasing) collector current of transistor 18.

In other words, even though the nonlinear base current of the second transistor 26 is supplied by the first transistor 18, the effect of β nonlinearity on the second transistor 26 is canceled out because the collectors are commonly connected.

FIG. 3 shows typical changes in β with respect to RF power and transistor collector current at 100 MHz.

As mentioned above, if we obtain the same gain as that of the prior art,
Since each stage has twice the negative feedback by the emitter resistor, the nonlinearity of the base-emitter voltage VBE can be reduced accordingly.

As explained above, the transistor amplifier of the present invention is
It has various extremely significant practical effects as described below.

(b) First, both transistors 18.26 have emitter resistors 24.28 of approximately equal resistance and are housed in a common housing so that they can operate at the same current level.

Therefore, by using both transistors at an operating point where the current amplification degree β of each transistor is large, a large output current can be obtained.

(b) Next, since both transistors 18 and 26 are connected in a quasi-Darlington type, the emitter resistance can be made larger than when using a single transistor with the same output current level, which increases negative current feedback and causes nonlinear Distortion can be reduced.

Furthermore, since the base of the subsequent transistor 26 is not directly connected to the input signal source, the input interference becomes higher than when both transistors are connected in parallel, which not only reduces distortion due to input signal source modulation but also increases current. The frequency will also be doubled.

(C) Thirdly, since both transistors 18 and 26 are housed in a common housing, the temperature characteristics are extremely stable.

Therefore, the amplifier of the present invention can convert frequencies from 50 kHz to 270 kHz, for example.
It exhibits extremely low distortion over a wide frequency range up to MHz and can generate power up to 0.2W.

The invention is particularly useful on the output side of signal generators which require good input-output isolation and linearity.

Although the above description describes only one preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the gist of the present invention.

For example, the transistor amplifier of the present invention is not NPN (
(PNP) transistors may be used, and it may also be used as a DC amplifier instead of an AC amplifier.

Furthermore, if necessary, three or more transistors may be similarly connected in a Darlington type.

[Brief explanation of drawings]

Fig. 1 is a schematic circuit diagram of a conventional transistor amplifier, Fig. 2 is a schematic circuit diagram of a preferred embodiment of the present invention, and Fig. 3 is a diagram showing typical changes in β with respect to collector current. 12 is an input signal source, 18 is a first transistor,
24 is a first resistor, 26 is a second transistor, 28 is a second resistor, and 32 is a load.

Claims (1)

[Scope of utility model registration request] a first transistor whose base is connected to the input signal voltage source and whose emitter is connected to the reference potential source via a resistor; whose base is connected to the emitter of the first transistor and whose emitter is connected to the potential source via the resistor; a second transistor connected to each other; the first and second transistors are connected to each other;
A transistor amplifier in which the emitter resistors have substantially equal resistances, are housed in a common housing, operate at substantially the same signal level, and obtain an output signal from their commonly connected collectors.