DE1909635A1 - Demodulator - Google Patents

Description

Dr .-! N5. HÄ? IS flÜS

Telefonaktiebolaget IM Eriesspn ^ S töckholm JS, Sctiweden-

Demodulator

The present invention relates to an arrangement that includes the Difference between the envelopes of two voltages, with ^ telt, e.g. for "demodulating amplitude-modulated or frequency modulated signals; , \ '

The demodulation of an amplitude-modulated signal is easily achieved by connecting the Signai with a Diode is rectified, and with the help of an integration network, which consists of a resistor and a parallel switched capacitance can exist ^ is the Hilllkurve des rectified signal, i.e. the modulating signal. There is a significant disadvantage in this regard

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the distortion obtained by having the diode a has non-linear current-voltage characteristic. Furthermore this characteristic of the diode is very temperature-dependent. Around To eliminate the disadvantages, one can use a diode instead of a use transistor connected as emitter follower and connect a capacitance in parallel to the emitter resistor, whereby the emitter circuit forms the necessary integration network. This results in a somewhat improved linearity, while on the other hand the temperature dependence of the arrangement continues. The above-mentioned arrangements which determine the envelope curve can also be used for demodulation a frequency modulated signal. Namely, if such a signal with the carrier frequency f on a first, the envelope determining arrangement via an inductance or on a second arrangement determining the envelope curve via a capacitance is given, then the difference between the outputs of the assemblies is proportional to the difference between the Frequency of the frequency-modulated signal and the frequency f with a suitable choice of the values of the inductance and the Capacity. The disadvantages mentioned above occur consequently also when demodulating a frequency-modulated signal. The purpose of the present invention is therefore Creation of an arrangement for demodulation in which particularly good linearity is obtained and which is practically independent is affected by temperature changes and changes in supply voltage. The characteristics of the arrangement emerge from the claim below.

The invention will be described in more detail with reference to FIG Description of the accompanying drawing, which shows a circuit diagram of an arrangement according to the invention.

In the drawing, two transistors are labeled T1 and T2, which are each connected to a DC voltage source E via a collector resistor R1 or R2. The emitters of the Transistors are connected to a common emitter resistance R3 to ground, with a capacitance C parallel to the emitter resistor

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is standing. A resistor r4 lies between the base of the Transistor Tlund cash register, the connection points of the resistor R ^ form the Eirigangslemmen Ia and Ib of the arrangement. Similarly, there is a resistor R5 between the base of the transistor ^ Ground connected, and its connections form the input terminals Ra and Rb for a reference voltage. About that In addition, the collectors of the transistors form the output terminals-Ua or Ub of the arrangement.

In the arrangement described above, which consists essentially of consists of a differential amplifier to which a capacitance C is added, the input terminals or the Reference voltage terminals supplied voltages from the base-emitter diode of the corresponding transistor rectified, and the difference between the rectified voltages becomes in the integration network from the resistance R ^ and the Capacity C integrated. This creates tension across the Get output terminals whose size is proportional to the difference. rence between the envelopes of the t-af supplied by the base electrodes Tension is. As a result, when an amplitude-modulated signal is applied to the input terminals and a DC voltage is applied to the reference voltage terminals, will be on the output terminals receive a signal whose size is proportional to the difference between the modulated signal and this DC voltage is. Due to the differential circuit, this proportionality is within a very large amplitude range obtained, and the characteristics of the arrangements are very little by changes in temperature or supply voltage influenced. In order to improve these characteristics further, the arrangement can of course also be combined with others Compensation means are provided which are known per se in connection with differential amplifiers.

When demodulation is used for frequency modulated signals is then these signals are partly to the input terminal Ia via a coil, partly to the reference voltage & terminal

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Ra given over a capacity. If, in this circuit, the inductance L of the coil and the capacitance C of the capacitor are chosen so that the relationship f _Q = ■: - 1. . :. ;

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is maintained, where f_ is the carrier frequency, then two signals with the same amplitude are obtained at the base electrodes of the transistors at the frequency f ". If the Frequency differs from the carrier frequency, then change it the amplitudes in opposite directions at the two base electrodes, and that at the output terminals Ua and Ub signal obtained is proportional to the difference between the Envelope curves of the signals delivered to the base electrodes, i.e. the degree of modulation.

Claim: ■ - * .- ■

90 98U71 15 p

Claims (1)

- 5 - T 1OP7 Claim: Arrangement for determining the difference between the ^ envelope curves of two voltages e.g. to demodulate an amplitude-modified one or frequency modulated signal, characterized by that it contains two transistors (Tl, T2) whose Collectors each with a collector resistor (Rl, R2) a DC voltage source (E) are connected and the emitter via a common emitter resistor (R] 5), to the one Capacitance (C) is connected in parallel, connected to \ ground, and that the arrangement has two input terminals (Ia, Ib) which are connected to the base of one of the transistors (Tl) or to ground are two voltage reference terminals (Ra, Rb) connected to the base of the other transistor (T2) or ground are connected, and has two output terminals (Ua, .Ub) which are connected to the collector electrodes of the transistors, with the Output terminals a voltage is obtained that is proportional the difference between the envelope curves of the reference terminals and the signals supplied to the input terminals. • Heipa./ -C- Lee rseiie "" S - -_ί 'Λ' I