INPUT STAGE OF AN AMPLIFIER AND CORRESPONDING AMPLIFIER

Abstract

The input stage (16) of a high-fidelity amplifier (10) with high linearity and a low distortion rate comprises:—an input (12) for the digital signal to be converted;—a voltage output (26) for the converted voltage;—a digital/analog converter (20), the input of which forms the input (12) for the digital signal to be converted, the digital/analog converter (20) having access to a signal terminal (24);—a voltage current conversion resistor (36) arranged between the voltage output (26) and a reference potential; and—a current/voltage converter (22) that has a voltage output and is arranged between the signal terminal (24) and the voltage outlet (26). The current/voltage converter (22) comprises a transistor (46). The source of the transistor (46) is only connected to the signal terminal (24) of the digital/analog converter (20).

Claims

1. An input stage (16) of an amplifier (10) comprising: an input for the digital signal to be converted; a voltage output for the converted voltage; a digital-to-analog converter, the input of which forms the input for the digital signal to be converted, the digital-to-analog converter having a signal terminal for generating a current; a resistance for converting the current into a voltage, connected to the voltage output and to a reference potential; and a current-voltage converter with a voltage output, connected to the signal terminal and to the voltage output, the current-voltage converter comprising a transistor such as the gate of the transistor is connected to a voltage source, the drain of the transistor is connected to a current source and the source of the transistor is connected to the digital-to-analog converter, the current source generating a continuous current, wherein the source of the transistor is exclusively connected to the signal terminal of the digital-to-analog converter and wherein the digital-to-analog converter is able to generate a current comprising a continuous component and a fixed component, the current source being able to provide a current equal to the continuous component of the current generated by the digital-to-analog converter, the digital-to-analog converter being connected between a fixed potential and the source of the transistor.

2. The input stage according to claim 1, wherein the digital-to-analog converter is with current absorption.

3. The input stage according to claim 1, wherein the input stage is made on an integrated circuit.

4. An amplifier comprising an input stage according to claim 1, and an amplification stage, connected in series with the input stage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention will be better understood upon reading the description which follows, exclusively given as an example and made with reference to the drawings wherein:

[0030] FIG. 1 is a schematic view of a high fidelity amplifier comprising an input stage according to the invention;

[0031] FIG. 2 is an electric diagram of an input stage of the amplifier of FIG. 1 according to the invention.

DETAILED DESCRIPTION

[0032] The amplifier 10, schematically illustrated in FIG. 1, is a hi-fi amplifier able to receive on an input 12 a digital signal and to produce on an output 14 an amplified analog signal.

[0033] As known per se, the amplifier 10 comprises an input stage 16 ensuring the conversion of the digital input signal into an output analog signal modulated in voltage, as well as an amplification stage 18, ensuring the supply of sufficient power for the load placed downstream, i.e. one or several loudspeakers. Preferably this is an amplification stage of class A.

[0034] The input stage 16 comprises a digital-to-analog converter 20, the input of which is connected to the input 12 of the amplifier for receiving a digital signal I.sub.digital. This digital-to-analog converter is able to provide a current-modulated analog signal I.sub.modulated. The digital-to-analog converter is for example a PCM 1792 from Texas Instruments.

[0035] The current I.sub.modulated comprises a variable component and a fixed component.

[0036] The output of the digital-to-analog converter 20 is connected to a current-voltage converter 22 according to the invention.

[0037] This current-voltage converter 22 is able to provide a modulated voltage V.sub.modulated with a voltage gain, from the modulated current I.sub.modulated produced by the digital-to-analog converter 20.

[0038] The output of the current-voltage converter 22 is connected to the input of the amplification stage 18, as known per se.

[0039] FIG. 2 illustrates the input stage 16 of the amplifier of FIG. 1.

[0040] In this FIG. 2, the digital-to-analog converter 20 is connected at the input to the input 12 of the amplifier 10 and has a signal terminal 24 for generating a current I.sub.modulated comprising a continuous component (DC component) and a fixed component. The digital-to-analog converter 20 is also connected to a ground.

[0041] The current-voltage converter 22 is connected to the signal terminal 24 of the digital-to-analog converter 20 and has a voltage output 26 able to be directly connected to the amplification stage 18.

[0042] The digital-to-analog converter 20 is schematized in FIG. 2 with two current sources 28 and 30. More specifically, the first current source 28 is able to generate the continuous component of the current I.sub.modulated at the output of the digital-to-analog converter 20. The second current source 30 as for it is able to generate the variable component of the current I.sub.modulated at the output of the digital-to-analog converter 20.

[0043] In FIG. 2, the digital-to-analog converter 20 is with current absorption and forms a current sink, commonly designated by “sink”. The expression “with current absorption” means that the current I.sub.modulated at the signal terminal 24 of the digital-to-analog converter 20 is absorbed; i.e., that if the conventional direction of the current illustrated by the arrow illustrating the current I.sub.modulated in FIG. 2 is directed towards the transistor 46 and not towards the digital-to-analog converter 20, the current I.sub.modulated is always negative.

[0044] The digital-to-analog converter 20 is for example a converter AD 1955 from Analog Devices.

[0045] The current-voltage converter 22 comprises a conversion resistance 36, one terminal of which is connected to the voltage output 26, and the other terminal of which is connected to a reference potential.

[0046] The resistance 36 is able to convert the current I.sub.modulated at the output of the digital-to-analog converter 20 into a voltage V.sub.modulated.

[0047] The current-voltage converter 22 further comprises at least one transistor 46 connected at its source to the digital-to-analog converter 22. In FIG. 2, only one transistor 46 is illustrated, however the current-voltage converter 22 may comprise several transistors 46.

[0048] The transistor 46 forms a cascode stage or with a common gate or base of the input stage 16.

[0049] The transistor 46 is for example a MOSFET transistor.

[0050] The current-voltage converter 22 also comprises a voltage source 42 connected to the gate of the transistor 46 of FIG. 2.

[0051] The current-voltage converter 22 further comprises a third current source 50 connected to the drain of the transistor 46.

[0052] The third current source 50 is able to generate a continuous bias current in the electric circuit of the input stage 16.

[0053] As visible in FIG. 2, the current-voltage converter 22 comprises a single current source 50 and the source of the transistor 46 is directly and exclusively connected to the current output of the digital-to-analog converter 20. In particular, no current source is connected between the transistor 46 and the digital-to-analog converter 20.

[0054] The current source 50 is such that the current generated by the current source 50 is equal to the current generated by the current source 28 of the digital-to-analog converter 20, therefore equal to the continuous component of the current I.sub.modulated, this in order to have in the transistor 46 a non-zero current regardless of the value of the digital input signal. Indeed, the variable component of the current I.sub.modulated is always less in absolute value to the continuous component of the current I.sub.modulated, so that the value of the latter is always of the same sign.

[0055] For example, if the continuous component of the current I.sub.modulated is equal to 3 mA and the variable component of this current I.sub.modulated is of 2 mA, then the current generated by the current source 50 is set to 3 mA.

[0056] The digital-to-analog converter 20 and the current-voltage converter 22 are made on a same integrated circuit, comprising a semi-conducting substrate, for example based on silicon. The integrated circuit is for example of the ASIC (acronym of Application-Specific Integrated Circuit) type.

[0057] Thus, such an input stage 16 of an amplifier gives the possibility of reducing the number of current sources of the current-voltage converter 22 by making use of the characteristics of the digital-to-analog converter 20.

[0058] Thus, such a circuit comprises less components and is therefore more compact to make on an integrated circuit and therefore less expensive.

[0059] Further, the reduction in the number of current sources decreases the risks of heating of the circuit and gives the possibility of saving energy.