FR2621189A1 - Device for reducing parasitic noise in the applications of digitally controlled amplifier attenuators - Google Patents

Abstract

The subject of the invention relates to a device for reducing parasitic noise in the applications of digitally controlled amplifiers or attenuators. Device for reducing parasitic noise, intended to be interposed between the digital control system and the digitally controlled attenuator or amplifier system 1 consisting of a pair of cascaded registers 2, 4 between which the transfer of data is synchronised with a signal through a window detector 3. It takes two forms. Firstly, in the absence of signal, each switching causes a very short small pulse produced by the transfers by capacitive couplings of the edges of variations of the control data. The level of this noise depends essentially on the quality of the components used.

Description

 The object of the invention relates to a device for the reduction of parasitic noise in the applications of digitally controlled attenuators or amplifiers.

 A digitally controlled amplifier is an electronic signal processing system that adjusts the gain or attenuation of the signal amplitude, by means of active switching on a resistor network.

 These switches are controlled by a logic system controlled or not by a microprocessor.

 The switch and resistance network assembly playing the role of a digital-analog converter.

 When using digitally controlled amplifiers in a sound processing unit, audible disturbances arise from these switches.

 They manifest themselves in two forms. First, in the absence of a signal, each switch causes a small, very short pulse, produced by the transfers by capacitive couplings of the edges of variations in the control data. The level of these noises depends essentially on the quality of the components used.

 Then, in the presence of a signal, more particularly a sinusoidal signal, the fact of switching the gain during an alternation produces an accident on the curve (fig 1). The higher the noise level, the higher the jump in gain or attenuation.

 The object of the invention eliminates these drawbacks and consists, on the one hand, of detecting on the signal to be processed the instant when each series of switching operations is to be carried out, and on the other hand of storing each new control value in coming from the logic system, so that the latter does not cause the switching operations until the instant detected.

 To this end, first to suppress the noise in the first case described above, it suffices never to cause switching in the absence of signal. Indeed, the variations in gain on a zero signal are devoid of interest, it then suffices to validate the last gain value retained, as soon as a signal appears.

 Then, in order to make the disturbance described in the description of the state of the art inaudible, it is necessary to cause each switching at the instant when the energy of the signal passes through a minimum, that is to say during its passage. to zero (fig 2).

 These improvements are obtained by triggering the gain switches by passing the signal close to zero.

In the accompanying drawings, given by way of explanation
Figure 1 shows the unsynchronized gain switches.

 Figure 2 shows the gain switches synchronized to zero.

 Figure 3 is a block overview of the device.

 Figure L shows a synchronous diagram.

 The device according to the patent must be interposed between the digital control system and the digitally controlled attenuator or amplifier system 1 used. It consists of a pair of cascade registers 2 and 4 between which the data transfer is synchronized to the signal by a window detector 3.

 The signal is then detected through a window detector 3 centered on zero. The latter begins to operate as soon as the signal reaches an amplitude to be chosen between -8dBm and -5dBm, depending on the desired dynamic range.

 The trailing edge of the pulse thus obtained, FIG. 4, is used to transfer the command value contained in the current register 4.

 The content of the current register directly controls the digital analog converter 5.

 The control system 1 must manage the loading of data into the buffer register 2.

 According to FIG. 4, 6 designates the analog input signal, 7 the data loaded by the control system, 8 the loading pulses, 9 the data in the current register, 10 the data loading pulses in the current register, 11 the analog output signal.

Claims (1)

CLAIMS 1 "Device for reducing parasitic noise in the use of digitally controlled attenuators or amplifiers having the object, on the one hand, of detecting on the signal to be processed the instant at which each series of switching operations and d on the other hand to store each new command value coming from the logic system, so that the latter does not cause the switching operations until the instant detected, characterized by the intercalation of the device between the control system and the amplifier digitally controlled, it consists of a pair of cascade registers (2,1) between which the transfer of data is synchronized to the signal by a window detector (3).  20 Device according to claim 1 according to which the result is obtained by a signal detected through a window detector (3) centered on zero and which begins to operate as soon as the signal reaches the desired amplitude, the trailing edge of the pulse thus obtained transfers the command value contained in the buffer register (2) to the current register (4) which in turn controls the digital analog converter (5) being specified that the control system (1) manages the loading of the data in the buffer register (2).