IL47901A - Transistor amplifiers - Google Patents

Description

Transistor amplifiers SIEKEttS A TIENffESELLaCHAFI C. 45501 The invention relates to transistor amplifiers of the type having a regulating component for controlling a sinusoidal output voltage.

In carrier-frequency, data-transmission equipment, all the pilots and control frequencies required for a system are generally obtained from one fundamental frequency which is produced by a fundamental generator.

The individual control frequencies are then amplified in respective control frequency amplifiers which are provided for them.

One object of the present invention is to provide a control frequency amplifier which is suitable to amplify any one of a plurality of control frequencies, wherein the outlay in components is kept low whilst maintaining adequate regulation of the output voltage.

The invention consists in a transistor amplifier in which a regulating component is provided to regulate a sinusoidal output voltage, the regulating component comprising a differential amplifier having one input connected to a reference voltage, and a second input connected to a rectified voltage obtained from the output signal which is to be regulated, said signal being obtained via a two-stage transistor amplifier which is connected in such manner that in the absence of an input voltage the first stage transistor is conductive and the second stage transistor is blocked, a rectangular voltage source being applied as an input voltage, and said one input of the differential amplifer being connected to the inpu^ of the second stage transistor.

By these measures one obtains an amplifier which may be regulated with simple means and which exhibits an ade-quate resistance to distortion.

Advantageously the reference voltage can be formed by a zener diode whose temperature response is selected with regard to the temperature response of the rectifier diode used to supply the operating voltage, which ensures exact compensation for temperature variations.

Preferably the rectifier arrangement which serves to rectify the output for monitoring purposes has its output connected to a L-element composed of a series resistor and a series combination of a resistor and a capacitor in a shunt arm.

This uanders short output voltage surges ineffective in respect of the regulating process.

Advantageously the amplifier is provided with means to operate with a rectangular voltage of 12 kHz or of 4 kHz, a voltage divider constructed from integrated circuit elements being used for 4 kHz operation.

Through the use of integBted circuit, the current requirement can be held equal both with and without frequency division. The zener diode voltage can be used not only to produce the reference voltage, but also act at the same time for the current supply of the frequency divider construced in the integrated circuitry technique since integrated circuit elements having a very low cur requirement are used.

The invention will now be described with reference to the drawings, in which:- Figure 1 is a schematic circuit diagram of one exemplary embodiment of the invention; and Figure 2 is a set of explanatory waveform diagrams.

Rectangular pulse trains of 4 kHz or 12 kHz are fed via a resistor R2 and coupling capacitor C2 to ihe base of a transistor Tl. On account of the RC-coupling, the ernitter-base-diode of this first transistor Tl is provided with a parallel diode D2 to enable the capacitor C2 to discharge.

In order to ensure that a second transistor T4 that is connected in a second amplifier stage following the first transistor Tl is blocked and the current comsumption therefore remain low in the event of non-operation, resistor R3 is required. The second stage transistor T4 is operated with a rectangular voltage of variable magnitude, a differential amplifier formed by transistors T2 and T3 being used for the amplitude regulation.

The zener diode Dl serves to provide a reference value for the transistor T2.

The required sinusoidal voltage is produced by a transformer Ul which is tuned by capacitors C5 and C6.

At 4kHz the tuning capacitance is transformed to give the required value.

Any stray resonance resulting from the transformation is eliminated by an RC-element formed by a resistor R13 and capacitor C7 connected in series in a shunt arm in order to improve the distortion factor. In order to achieve the requisite switch-over times from operation to substitute, a fundamental load resistor R12 is provided, and an RC element formed by the series combination of a resistor R8 and a capacitor C3.

The mode of functioning of the arrangement is as fol lows : When there is no signal at the input, the transistor Tl is conductive and the transistor T4 is blocked. As soon as a signal appears at the input of the transistor Tl, the transistor T4 is rendered conductive. The rectangular current supplied via the collector of the transistor T4 is transformed into a sinusoidal voltage with the aid of the transformer Ul and the capacitances C5 and C6. A part of this sinusoidal voltage passes via the rectifier circuit formed by D3, C4, RIO and the subsequent L-element R9 , R8 and C3 which serves to render ineffective any voltage surges, and is fed to the base of the transistor T3 of the differential amplifier As soon as the voltage at the base of the transistor T3 is greater than the reference voltage produced by the zener diode D at the base of the transistor T2 of the differential amplifier, the transistor T3 is rendered conductive and the transistor T2 is blocked. The base potential of the transistor T4 is thus altered in the sense required for compensation of any voltage fluctuations, so that the output voltage remains constant.

The use of a rectangular input voltage in both amplifier transistors substantially increases the efficiency in comparison to amplifiers employing sinusoidal voltage drive facilities. Adequate distortion clearance at the output can be attained by appropriate dimensioning of the oscillating circuit values. In addition to the a.c. voltage output the amplifier also possesses a d.c. voltage output for monitoring and an a.c. voltage output for a measuring device which is to be connected. A filter transistor T5 is connected in the current supply line in order to increase secondary wave suppression.

The transistor T5 has an emitter resistor R20 dimensioned in such manner that in the event of a short-circuit within the amplifiers, the current cannot exceed a given value.

A relay RS serves to switch over from normal operation to substitute operation when actuated by a multiple monitoring unit arranged at the exterior of the amplifiers.

Figure 2 is a set of explanatory waveform diagrams illustrating the mode of functioning of a three-component divider which is connected prior to the amplifier, and used when the amplifier is to be operated at 4kHz, to divide the rectangular voltage of 12 kHz which is normally available for operation. Line _a shows the 12 kHz pulse train, line b shows the output voltage of a first flip-flop, line c_ shows the output voltage at the output of a NOR-gate IC2, line _d shows the output voltage that would appear across the flip-flop 2 in the absence of linking, and line _e shows the output voltage that is obtained by linking the flip-flop to the NOR-gate. The mode of functioning is as follows: The two flip-flop are connected in a divide-by-three configuration.

If the pulse train *Q from the first flip-flop is fed to an input of the NOR-gate, and the latter's output pulse is fed to a reset of the second-flip-flop, a symmetrical divider ration s then obtained at the output Q of the second flip-flop.

Claims (5)

WHAT WE CLAIM IS:

1. A transistor amplifier in which a regulating component is provided to regulate a sinusoidal output voltage, the regulating component comprising a differential amplifier having one input connected to a reference voltage, and a second input connected to a rectified voltage obtained from the output signal which is to be regulated, said signal being obtained via a two-stage transistor amplifier which is connected in such manner that in the absence of an input voltage the first stage transistor is conductive and the second stage transistor is blocked, a rectangular voltage source being applied as an input voltage, and said one input of the differential amplifier being connected to the input of the second stage transistor.

2. A transistor amplifier as claimed in Claim 1, in which said reference voltage is formed by a zener diode whose temperature response is selected to compensate the temperature response of a diode used to rectify the output signal.

3. A transistor amplifier as claimed in any preceding Claim, in which a rectifier arrangement is provided to rectify the output signal, which arrangement has its output connected to an L-element which consists of a series resistor and a series combination of a resistor and a capacitor in a shunt arm.

4. A transistor amplifier as claimed in any preceding Claim, in which the amplifier is designed to operate with rectangular input waveform at 12 kHz or 4kHz, a voltage divider constructed from integrated circuit elements being used to produce the 4kHz input.

5. A transistor amplifier substantially as described with reference to Figure 1.