DE3230606A1 - CURVE DETECTOR - Google Patents

Description

Leonhard Richard Kahn, 137 East 36th Street, New York, N.Y. 10016 / USA

'Envelope detector

The invention relates to an envelope detector for receiving an amplitude-modulated carrier signal.

With a typical receiver for amplitude modulated monaural high frequency signals becomes the first stage formed by a superhet circuit (superhet mixer), which converts the high frequency signal into an intermediate frequency signal (IF signal) converts. The envelope of this signal, which corresponds to the amplitude modulation, is then demodulated, i.e. the IF signal becomes a Generates signal that is equivalent to amplitude modulation. This envelope demodulation can be done with the help of a Series connection of a diode and a low-pass filter can be achieved, with a half-wave rectification at the diode of the signal takes place. On the other hand, the envelope curve demodulation can also be done with an in-phase one Product demodulator can be achieved in which the IF signal is multiplied by a signal, whose frequency and phase are the same as that of the carrier. · The higher order harmonics and high frequency interference are then filtered out with the help of a low-pass filter.

In a known system for AM stereo broadcasting, the carrier is amplitude-modulated with a signal that is the sum of the L + R stereo information in the listening area (L + R), the carrier also being phase modulated with a signal equal to the difference of the

3230601

Corresponds to stereo signals (L-R). A receiver for such a broadcast signal is disclosed in U.S. Patent No. 4,108,994 or DE-OS 26 19 440 described. In one embodiment of this receiver a synchronous demodulator is used used as an envelope detector to recover the L + R signal.

Neither with a mono nor with a stereo receiver is subject to an envelope curve detector, which is built up with a diode or with a same-phase product demodulator is, fading problems or problems of decreased selectivity. In particular, a diode detector cannot distinguish between the desired carrier and a stronger interference carrier that is in the IF passband falls. For an in-phase product demodulator, the difficulties arise due to occurring Phase modulations, which are a common occurrence in AM broadcasters.

The object of the invention is therefore to improve the selectivity and the fading resistance of an AM receiver through the use an envelope demodulator that supports both in-phase and quadrature demodulation used.

The envelope detector according to the invention is used to achieve this object characterized by the features of the main claim.

The received and. AM signal converted into the IF band is fed to two product demodulators. The carrier of the IF signal is for example by means of a PLL circuit separated and a corresponding carrier with 90 ° phase is generated, i.e. the separated one Carrier is rotated 90 ° in phase. The carrier

323060a

with the original phasing becomes one of the demodulators and the carrier with the quadrature phase is supplied to the other demodulator. The output signals of the demodulators are squared separately from each other and then added: The resulting signal becomes the The square root is taken to produce the final envelope corresponding to the signal. By using of product demodulators, i.e. a synchronous demodulation, the suppression of strong interference carriers is possible. Also, using the in-phase and quadrature-demodulated signals insensitive to the envelope demodulation process occurring phase modulation of the transmitter.

323060a

The single figure shows the block diagram of a synchronous Envelope detector according to the invention.

In a stereo system as described in US Pat. No. 4,018 corresponding to DE-OS 26 19 440, the essential parts are included in the following by reference, the broadcast signal has an amplitude-modulated Component corresponding to the L + R stereo information and a phase modulated component corresponding to the L-R stereo information. When the same or in-phase signal component through is represented by a vertical vector, the quadrature phase component is represented by a horizontal one or horizontal vector. This allows the envelope modulation of the broadcast signal through a vector can be illustrated whose "angle varies between 0 and 90 ° and whose amplitude equal to the square root of the sum of the squares of the in-phase component (I) and the quadrature component

2 2

(Q), i.e. I + Q is. The circuit illustrated in the figure made possible by generating the in-phase component (I) in the product demodulator 104 and the quadrature phase component (Q) in the product Demodulator 108 is an envelope demodulation. To generate the for the product demodulators 104 and required IF signal is a composite amplitude and phase modulated high frequency signal (RF signal) received by an antenna and by a common (not shown) superhet circuit processed, in which the corresponding ZFr signal is generated. This IF signal is not only the product demodulators 104 and 108, but it is also fed into a circuit 102 for Separating the carrier supplied. As stated in the above-mentioned document, the carrier separation can be achieved by means of a PLL circuit.

3230600

The separated carrier is then fed into a phase shift circuit 106 in which an in-phase and generating a carrier signal rotated by 90 phase. However, such signals are already occurring AM stereo receivers, as described in the above DE-OS.

The output of the product demodulator 104 is fed to a low pass filter (LPF) 110, while the The output signal of the product demodulator 108 passes into a low-pass filter 112. It is necessary that the Product demodulator 104 and the low-pass filter 110 die Let through direct voltage component, which results from multiplying the IF signal with the carrier. It is also useful if the DC voltage component in the quadrature path is via the product demodulator 108 and the low pass filter 112 are obtained remain. However, there are certain situations where this may be unnecessary. The low pass filters 110 and may provide improved selectivity assuming that product demodulators 104 and have low distortion properties. For example an active filter with five poles can be built cost-effectively. Such a filter gives at 10 kHz an attenuation of 45 db and at 5 kHz an attenuation of 1 db; At 5.4 kHz, the signal would be reduced by 6.6 db. Although not always necessary, it is It is advantageous to provide a certain selectivity in the IF circuit in order to override the product demodulators to avoid .. The selectivity achieved by the low-pass filters 110 and 112 is symmetrical, what useful in most AM reception situations is, however, its main advantage is that the use of two active low-pass filters is possible, the can be constructed using integrated circuit techniques instead of a more difficult one.

IF filter to be delivered.

The signals come from the low-pass filters 110 and 112

2 into squaring circuits 114 and 116 where the I - and

2
Q signals are generated. These signals are then combined with one another in an adding circuit 118 and the sum signal generated is fed into a square rooting circuit 120 which generates the desired envelope curve-demodulated output signal which is present at connection 122.

Claims (3)

323060a '! Patentanwälte' Dipf .- 'ing. W. Scherrmann Dr.-Ing. R. Roger 7300 Esslingen (Neckar). Webergasse 3. Postfach 17 August 1982 Telephone PA 3 baeh 'Stuttgart (0711) 356539 35 9619 Telex 07 256610 smru telegrams patent protection Esslingenneckar patent claims 1. / Envelope detector for a received envelope modulated Carrier signal, characterized in that one of the received envelope curve modulated Carrier signal (IF) a carrier signal with the same phase and a carrier signal with quadrature phase generating circuitry (102, 106) and first and second product demodulators (104, 108) are provided are, wherein in the first, a first demodulated signal generating product demodulator (104) the received envelope curve-modulated carrier signal (IF) as well as the separated carrier signal same phase and into the second, a second demodulated signal generating product demodulator the received envelope-modulated carrier signal (IF) and the separated carrier signal with quadrature phase is fed that for squaring the first and the second demodulated signal the first product demodulator (104) to a first squaring circuit (114) and to the second product demodulator (108) a second squaring circuit (116) are connected, the output signals an adder circuit (118) are supplied, in which is the sum of the squared first demodulated signal and the squared second demodulated Signal is generated, and that a square rooting circuit (120) is connected to the adding circuit (118) 3230601 is closed, which works as a function of the sum signal and whose output signal is proportional is the square root of the sum signal and the Amplitude corresponds to the envelope of the received envelope-modulated carrier signal. 2. Envelope detector according to claim 1, characterized in that the circuit (102, 106) for generating of the separated carrier signals with the same phase and quadrature phase depending on PLL circuit (102, 106) (phase-locked loop) operating on the received envelope-modulated carrier signal (IF) having an unmodulated carrier signal with the same frequency and phase as the received one generated envelope-modulated carrier signal, and a 90 phase shifter circuit (106), which consists of derives the separated carrier signal with quadrature phase from the output signal of the PLL circuit (102). 3. Envelope detector according to one of the preceding Claims, characterized in that at the output of the first and the second product demodulator (104, 108) each have a low-pass filter (110, 112) connected.