DE1180803B - Broadband transistor amplifier - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Class: H03f

German class: 21 a4- 29/01

Number: 1180 803

File number: T 24337IX d / 21 a4

Filing date: July 20, 1963

Opening day: November 5, 1964

The invention is concerned with a multistage broadband amplifier for high frequencies with transistors in emitter circuit.

Broadband amplifiers are to be understood here as amplifiers and their usable bandwidth is several hundred MHz and its upper limit frequency is in the decimeter wave range.

Such amplifiers are suitable as antenna amplifiers or as an amplifier for impulses with very steep rising edges, since they have a small self-rising time and therefore only slightly distort the edge of the pulse to be amplified.

In tube technology, the principle of the chain amplifier has established itself for the construction of such amplifiers. However, the effort for this is considerable, since the product of bandwidth and gain modern tubes is only about 200 to 300 MHz.

In the case of special pulse amplifiers, it is also already known to use them with transformer coupling between to build up the individual levels. Since the lower frequency band is severely cut here, is this amplifier design is often a disadvantage.

When using transistors, the ratios are more favorable. It can be used as an amplifier build, which consist of several stages connected in cascade and bandwidths of several hundred MHz. In circuits with small load resistances, such as those in broadband technology The frequency at which the current amplifier is common is the common emitter circuit working transistor becomes one, one with the product of gain and bandwidth in tube technology analog size. The frequency mentioned is generally referred to as the / ^ cut-off frequency. There Transistors are already available on the market today with a / ^ cut-off frequency greater than 1 GHz, broadband amplifiers can be used using the means known from tube technology build which can be used up to high frequencies. The bandwidth of such a transistor stage however, is only a fraction of the / S cutoff frequency.

The aim of the present invention is to show a broadband amplifier that is as possible has a linear gain curve and has an upper limit frequency which is at least equal to the / ^ - cutoff frequency of the transistors used.

Based on a multistage broadband amplifier for high frequencies with transistors in a common emitter circuit, the invention therefore proposes that to increase the gain up to frequencies above the _/ Ö ₁ limit frequency of the transistor broadband amplifier

Applicant:

Telefunken patent collecting company

m. b. H., Ulm / Danube, Elisabethenstr. 3

Named as inventor:

Dipl.-Ing. Horst Klink, Braunschweig

Transistors are used as coupling elements between the transistors and the load lines whose length is A _0/5 to λ _0/5 and whose characteristic impedance is between 100 and 300 ohms, where X ₀ denotes the wavelength at the upper end of the amplification range.

This will be explained in more detail with reference to the figure, based on an amplifier made up of two transistors Π and Γ 2. The output of the first transistor T1, which is operated in the emitter circuit, is coupled to the input of the second transistor T1, which is also operated in the emitter circuit, through a line section L _1. A line is also inserted as a coupling element between the output of the second transistor T1 and the load denoted by Y _2. With appropriate dimensioning of the lines L ₁ and L ₂ used as coupling elements, the interaction of the impedance and voltage transformation with the transistor parameters results in an almost constant gain curve depending on the frequency over an octave. The upper limit frequency of the amplifier is placed in the vicinity of the aforementioned / ^ limit frequency of the transistors.

The characteristic impedances of the lines L ₁ and L ₂ are large, so that the line is mismatched with the small terminating resistances (the input resistance of a transistor operated in an emitter circuit is generally small at the frequencies considered). _{According to the invention, the line lengths} are in the order of magnitude of λ 0/5 to A _0/8 , with ^ ₀ denoting the wavelength at the upper limit of the pass band. The optimal values for the characteristic impedance of the lines depend on the transistor type used. Useful results are obtained with a characteristic impedance between 100 and 300 ohms.

409 710/287

To calculate the gain and to determine the line parameters it is advisable to proceed from the four-pole parameters of the transistor in conductance position:

Ya = G ₁₁ + Jb ₁₁ = G ₁ (S) ( ^la >

Y ₁₂ = G ₁₂ + Jb _n = G ₂ (f) (Ib)

Y ₂₁ = G ₂₁ + Jb ₂₁ = G ₃ (J) (Ic)

Y * = G _n + Jb _n = GW (Id)

The following applies to the complex voltage amplification of a transistor stage

as «=

-Y,

21

If a line is now connected between the load conductance Y ₂ and the transistor, the amplification factor, taking into account the impedance and voltage transformation, applies to the amount of the amplification

■ S3 «; =

H ₁

+ j Y _e Z sin ft) + Y ₂ cos ß _l +

^J _z sin ft

So that the gain is constant over a larger frequency range, the course of Y ₉ and that of the denominator must be similar to one another.

as a function of / J ₁ makes the minimum, namely at the desired upper limit frequency of the stage, which is generally the size of the

Since * Y _{21 is} given, the denominator must therefore be at -20 / 3 _r limit frequency. The wave resistance is going to be adjusted. A good approximation for this is as a parameter. / J _{1 is} calculated from the possible if you print the amount of the denominator

arc tan <-

2 cd-from

1 -a ² + b * -c * + d * ~ 2 cd-ab

+ 1

with β = - ~ ί- =

In =; - to the
C. Phase measure the line a = G ₂ , (5 a) b = -G ₂₂ + , + G ₂ , ^ ₂₂ ) Z, (5b) c = = Q> i K), (5 c) -φ. , G ₂₂ 2 +

d - (G ₂₂ G ₂ - b ₂₂ b ₂ ) Z + -

(5d)

35

With the associated value pairs of Z and / J ₁ , the gain can be calculated according to equation (5) as a function of the frequency. As already mentioned, the optimal value of the characteristic impedance Z depends on the type of transistor used, ie on the frequency dependence of the four-pole parameters F ₂₁ and F _22. If the characteristic impedance of the coupling line L ₁ or L _{2 is} chosen to be significantly greater than 300 ohms, the gain is increased, but the gain curve is no longer as uniform as a function of the frequency

The course of the gain is also determined by the type of terminating resistance of the line. If the load F has only a small reactive component, a practical result results constant gain curve over an octave, based on the upper limit frequency of the amplifier. It is therefore advisable to design the load F accordingly. On the other hand, if the load has one If the reactive component is large, there is a maximum gain at the upper limit frequency and a maximum towards lower frequencies. Since this occurs iteratively in a multi-stage amplifier, the extreme value becomes quite pronounced. In this case, however, leveling is possible by that the last stage is designed for a lower frequency. It is also possible through a frequency-dependent Negative feedback even with a large reactive component of the load due to frequency-dependent ones To achieve negative feedback a leveling of the gain curve.

The lines for the coupling elements are preferably implemented by ribbon lines, however Depending on the frequency range for which the amplifier is designed, other lines such as For example, coaxial lines or waveguides are used.

Claims (3)

Patent claims: 1. Multi-stage broadband amplifier for high frequencies with transistors in common emitter circuit, characterized in that to increase the gain up to frequencies above the / Jj cut-off frequency of the transistors as coupling elements between the transistors and the load lines are used whose length A _0/5 to λ _{o is 8} and its wave impedance is between 100 and 300 ohms, where λ ₀ denotes the wavelength at the upper end of the gain range. 2. Amplifier according to claim 1, characterized in that the coupling lines are ribbon lines are. 3. Amplifier according to claim 1 or 2, characterized in that the to the amplifier connected load has only a small reactive component. 1 sheet of drawings 409 710/287 10.64 ι Bundesdruckerei Berlin