FR3074380A1 - ELECTRONIC OSCILLATOR BASED ON MOS TRANSISTORS - Google Patents

Abstract

The invention relates to an oscillator comprising: first (M1) and second (M2) MOS transistors; a first capacitor (C1) having a first electrode connected to the gate of the first transistor, and a second capacitor (C2) having a first electrode connected to the gate of the second transistor; a first resistor (Rg1; Rg1a) connecting the first electrode of the first capacitor (C1) to the drain of the first transistor, and a second resistor (Rg2; Rg2a) connecting the first electrode of the second capacitor (C2) to the drain of the second transistor; and a cross link circuit adapted to apply, between a second electrode of the first capacitor (C1) and the source of the first transistor, a voltage representative of the drain-source voltage of the second transistor, and, between a second electrode of the second capacitor ( C2) and the source of the second transistor, a voltage representative of the drain-source voltage of the first transistor.

Description

ELECTRONIC OSCILLATOR BASED ON MOS TRANSISTORS

Field

The present application relates to the field of electronic oscillators. It relates more particularly to an electronic oscillator produced on the basis of MOS transistors.

Presentation of the prior art

FIG. 1 is a conventional electrical diagram of an electronic oscillator produced on the basis of bipolar transistors.

The oscillator of FIG. 1 comprises two bipolar NPN transistors T1 and T2 connected in parallel between high V + and low V- nodes for applying a DC supply voltage. The transistor Tl has its emitter (e) connected to the node V-, and its collector (c) connected to the node V + via a resistor Rcl. The transistor T2 has its emitter (e) connected to the node V-, and its collector (c) connected to the node V + via a resistor Rc2. The base (b) of the transistor Tl is connected to the node V + via a resistor Rbl, and the base (b) of the transistor T2 is connected to the node V + via a resistor Rb2. The base (b) of the transistor Tl is further connected to the collector (c) of the transistor T2 via a capacitor Cl, and the base (b) of the transistor T2 is connected to the collector (c) of the transistor Tl by through a capacitor C2.

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The operation of the oscillator of FIG. 1 is as follows. Considering an operating phase in which the transistor T2 is closed (on) and the transistor Tl is open (blocked), the transistor T2 receives on its base (b) a first current coming from the resistor Rb2, to which is added a second current from the resistor Rcl and passing through the capacitor C2. This second current causes the capacitor C2 to charge. The base-emitter voltage of transistor T2 in the closed state is equal to the direct voltage drop of a PN junction, for example of the order of 0.7 V. The capacitor Cl, charged during a previous phase of closing of the transistor Tl and opening of the transistor T2, applies a negative voltage (relative to the node V-) on the base of the transistor Tl, which keeps the transistor Tl in the open state. A current flows through the resistor Rbl, the capacitor Cl and the transistor T2, causing a progressive rise in the voltage applied to the base of the transistor Tl. When the base-emitter voltage of the transistor Tl reaches the threshold voltage of the transistor Tl, for example of the order of 0.7 V, a base-emitter current flows in the transistor Tl, causing it to close. The closure of the transistor Tl causes its collector-emitter voltage to drop to a value equal to the saturation voltage of the transistor, for example of the order of 0.3 V. The capacitor C2, now charged, then applies a negative voltage on the base of transistor T2, which causes transistor T2 to open. The transistor T2 remains open as long as its base-emitter voltage rises to a value equal to its threshold voltage under the effect of the current flowing through the resistor Rb2, the capacitor C2, and the transistor Tl. A new switching occurs then, and the cycle begins again.

An oscillating operation is therefore obtained in which each of the two transistors T1 and T2 is alternately closed while the other transistor is open, and open while the other transistor is closed.

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To increase the frequency of the oscillations and / or decrease the power consumption, it would be desirable to be able to produce an oscillator based on MOS transistors rather than based on bipolar transistors.

The assembly of FIG. 1 is however not directly transposable to MOS transistors. Indeed, if we replace the transistors T1 and T2 of the assembly of FIG. 1 by N channel MOS transistors, we observe that the circuit is placed in a stable state in which the gates of the two transistors are charged at a voltage substantially equal to the supply voltage V +, and the two transistors conduct simultaneously.

summary

Thus, one embodiment provides an electronic oscillator comprising:

first and second MOS transistors;

a first capacitor, a first electrode of which is connected to the gate of the first transistor, and a second capacitor, a first electrode of which is connected to the gate of the second transistor;

a first resistor connecting the first electrode of the first capacitor to the drain of the first transistor, and a second resistor connecting the first electrode of the second capacitor to the drain of the second transistor; and a cross-link circuit adapted to apply, between a second electrode of the first capacitor and the source of the first transistor, a voltage representative of the drain-source voltage of the second transistor, and, between a second electrode of the second capacitor and the source of the second transistor, a voltage representative of the drain-source voltage of the first transistor.

According to one embodiment, the cross link circuit comprises a direct connection between the source of the first transistor and the source of the second transistor, a direct connection between the second electrode of the first capacitor and the

B15362 - DD17349ST drain of the second transistor, and a direct connection between the second electrode of the second capacitor and the drain of the first transistor.

According to one embodiment, the oscillator comprises first and second nodes for applying a DC supply voltage, the sources of the first and second transistors being connected to the first node, the drain of the first transistor being connected to the second node via a first load, and the drain of the second transistor being connected to the second node via a second load.

According to one embodiment, the first and second charges are resistive charges.

According to one embodiment, the first and second charges are inductive charges.

According to one embodiment, the oscillator comprises a transformer comprising a primary winding having a first end connected to the drain of the first transistor and a second end connected to the drain of the second transistor, and a secondary winding magnetically coupled to the primary winding.

According to one embodiment, the primary winding comprises a midpoint connected to the second node via an inductor.

According to one embodiment, the primary winding does not have a midpoint, a first end of the primary winding being connected to the second node by means of a first inductor and a second end of the primary winding being connected at the second node via a second inductor.

According to one embodiment, the oscillator further comprises a third MOS transistor connected in series with the first transistor, between the drain of the first transistor and the second node, and a fourth MOS transistor connected in series with the first transistor, between the drain of the second transistor and the second node, the gates of the third and fourth transistors

B15362 - DD17349ST being connected to the same node for applying a fixed bias potential.

According to one embodiment, the first and second MOS transistors are connected in series, the cross-link circuit comprising:

a third capacitor and a first transformer adapted to apply, between the second electrode of the second capacitor and the source of the second transistor, a voltage representative of the drain-source voltage of the first transistor; and a fourth capacitor and a second transformer adapted to apply, between the second electrode of the first capacitor and the source of the first transistor, a voltage representative of the drain-source voltage of the second transistor.

According to one embodiment:

the first transformer includes a first primary winding and a first secondary winding magnetically coupled;

the second transformer includes a second primary winding and a second secondary winding magnetically coupled;

the third capacitor has a first electrode connected to the drain of the first transistor and a second electrode connected to a first end of the first primary winding, the second end of the first primary winding being connected to the source of the first transistor;

the fourth capacitor has a first electrode connected to the drain of the second transistor and a second electrode connected to a first end of the second primary winding, the second end of the second primary winding being connected to the source of the second transistor;

the first secondary winding has a first end connected to the second electrode of the second capacitor and a second end connected to the source of the second transistor; and

B15362 - DD17349ST the second secondary winding has a first end connected to the second electrode of the first capacitor and a second end connected to the source of the first transistor.

According to one embodiment, the oscillator further comprises:

a first diode connected in series with the first resistor between the gate and the drain of the first transistor, the first diode being mounted directly between the gate and the drain of the first transistor; and a second diode connected in series with the second resistor between the gate and the drain of the second transistor, the second diode being mounted directly between the gate and the drain of the second transistor (M2).

According to one embodiment, the oscillator further comprises:

a third diode and a third resistor connected in series between the gate and the drain of the first transistor, in parallel with the series association of the first resistor and the first diode, the third diode being mounted in reverse between the gate and the drain of the first transistor; and a fourth diode and a fourth resistor connected in series between the gate and the drain of the second transistor, in parallel with the series association of the second resistor and the second diode, the fourth diode being mounted in reverse between the gate and the drain of the second transistor.

According to one embodiment, the oscillator further comprises a third resistor connecting the gate of the first transistor to a node for applying a fixed bias potential, and a fourth resistor connecting the gate of the second transistor to a node of application of a fixed bias potential.

Brief description of the drawings

These and other features and advantages will be discussed in detail in the following description of modes of

B15362 - DD17349ST particular embodiment made without implied limitation in relation to the attached figures among which:

FIG. 1, previously described, is an electrical diagram of an electronic oscillator produced on the basis of bipolar transistors;

FIG. 2 is an electrical diagram of an example of an electronic oscillator produced on the basis of MOS transistors according to a first embodiment;

Figure 3 is an electrical diagram of an alternative embodiment of the oscillator of Figure 2;

Figure 4 is an electrical diagram of another alternative embodiment of the oscillator of Figure 2;

FIG. 5 is an electrical diagram of an exemplary embodiment of a DC / DC conversion circuit comprising an oscillator of the type described in relation to FIG. 2;

FIG. 6 is an electrical diagram of another exemplary embodiment of a DC / DC conversion circuit comprising an oscillator of the type described in relation to FIG. 2;

Figure 7 is an electrical diagram of another alternative embodiment of the oscillator of Figure 2;

FIG. 8 is an electrical diagram of an exemplary embodiment of a DC / DC conversion circuit comprising an oscillator of the type described in relation to FIG. 7; and FIG. 9 is an electrical diagram illustrating an example of an electronic oscillator produced on the basis of MOS transistors according to a second embodiment.

detailed description

The same elements have been designated by the same references in the different figures. For the sake of clarity, only the elements useful for understanding the described embodiments have been shown and are detailed. In particular, the set of uses which can be made of oscillators of the type described in the present application has not been detailed, the embodiments described being compatible with the usual uses of electronic oscillators

B15362 - DD17349ST made on the basis of transistors. Unless specified otherwise, the expressions approximately, substantially, and of the order of mean to 10%, preferably to 5%. In the present description, the term connected is used to denote a direct electrical connection, without an intermediate electronic component, for example by means of one or more conductive tracks, and the term coupled or the term connected, to denote either a direct electrical connection (meaning then connected) or a link via one or more intermediate components (resistor, diode, capacitor, etc.). Furthermore, in the present description, unless otherwise specified, the voltages mentioned are all referenced with respect to a node V- of application of a low supply potential of the circuits described.

FIG. 2 is an electrical diagram of an example of an electronic oscillator produced on the basis of MOS transistors according to a first embodiment.

The oscillator of FIG. 2 comprises two N-channel MOS transistors Ml and M2, for example identical to the manufacturing dispersions, connected in parallel between high V + and low V- nodes for applying a DC supply voltage .

In the example of FIG. 2, the transistor Ml has its source (s) connected to the node V- and its drain (d) connected to the node V + via a resistor Rdl. More particularly, in the example shown, the resistance Rdl has a first end connected to the drain of the transistor Ml and a second end connected to the node V +. Similarly, the transistor M2 has its source (s) connected to the node V-, and its drain (d) connected to the node V + via a resistor Rc2. More particularly, in the example shown, the resistance Rd2 has a first end connected to the drain of the transistor M2 and a second end connected to the node V +.

The oscillator of FIG. 2 further comprises a resistor Rgl connecting the gate (g) of the transistor Ml to the drain of the transistor Ml, and a resistor Rg2 connecting the gate (g) of the

B15362 - DD17349ST transistor M2 at the drain of transistor M2. More particularly, in the example of FIG. 2, the resistor Rgl has a first end connected to the gate of the transistor Ml and a second end connected to the drain of the transistor Ml, and the resistor Rg2 has a first end connected to the gate of the transistor M2 and a second end connected to the drain of transistor M2.

The oscillator of FIG. 2 further comprises a capacitor C1 connecting the gate of the transistor Ml to the drain of the transistor M2, and a capacitor C2 connecting the gate of the transistor M2 to the drain of the transistor Ml. More particularly, in the example shown, the capacitor C1 has a first electrode connected to the gate of the transistor M1 and a second electrode connected to the drain of the transistor M2, and the capacitor C2 has a first electrode connected to the gate of the transistor M2 and a second electrode connected to the drain of the transistor Ml.

The operation of the oscillator of FIG. 2 is as follows. We consider an operating phase in which the transistor M2 is closed (on) and the transistor M1 is open (blocked). A negative voltage is applied to the gate of the transistor Ml via the capacitor Cl, which keeps the transistor Ml blocked, and a positive voltage is applied to the gate of the transistor M2 via the capacitor C2, which keeps the the transistor M2 passing. During the conduction phase of the transistor M2 and the blocking of the transistor Ml, the capacitor C2 is crossed by a current passing through the resistor Rdl, the capacitor C2, the resistor Rg2 and the transistor M2. The capacitor Cl is in turn crossed by a current passing through the resistance Rdl, the resistance Rgl, the capacitor Cl, and the transistor M2. When the first of the two following phenomena A and B occurs, a switching of the oscillator occurs, that is to say that the transistors M1 and M2 pass respectively to the closed state and to the open state.

Phenomenon A

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Under the effect of the current passing through the capacitor Cl, the gate voltage of the transistor Ml rises until reaching a value equal to the threshold voltage of the transistor Ml, for example of the order of 3 V. This causes the closure of the transistor Ml. This results in a drop in the voltage between the drain and the source of the transistor Ml, which leads to the application, via the capacitor C2, of a negative voltage on the gate of the transistor M2, causing the blocking of the transistor M2. The blocking of the transistor M2 leads to an increase in its drain-source voltage, which leads to the application, via the capacitor Cl, of a positive voltage on the gate of the transistor Ml, favoring the maintenance in conduction of the transistor ml.

Phenomenon B

Under the effect of the current passing through the capacitor C2, the gate voltage of the transistor M2 drops below the threshold voltage of the transistor M2, for example of the order of 3 V. This causes the transistor M2 to open. This results in an increase in the voltage between the drain and the source of the transistor M2, which leads to the application, via the capacitor Cl, of a positive voltage on the gate of the transistor Ml, causing the closure of the transistor Ml. The closing of the transistor Ml causes a drop in its drainsource voltage, which leads to the application, via the capacitor C2, of a negative voltage on the gate of the transistor M2, reinforcing the blocking of the transistor M2.

The transistors Ml and M2 remain closed and open respectively until the gate voltage of the transistor Ml goes back down to a value lower than its threshold voltage (phenomenon B), or until the gate voltage of the transistor M2 rises to a value greater than its threshold voltage (phenomenon A). A new switching then occurs and the cycle begins again.

An oscillating operation is therefore obtained in which each of the two transistors Ml and M2 is alternately

B15362 - DD17349ST closed while the other transistor is open, and open while the other transistor is closed.

The frequency of the oscillations and the duty cycle of the openings and closings of the transistors Ml and M2 depend in particular on the time constants Rgl * Cl and Rg2 * C2.

By way of example, the capacitors Cl and C2 have substantially identical values, and the resistors Rgl and Rg2 have substantially identical values, so as to ensure the conduction times of the transistors Ml and M2 substantially identical.

Figure 3 is an electrical diagram illustrating an alternative embodiment of the oscillator of Figure 2, to promote one or the other of the two causes of switching A and B above, namely the rise of the gate voltage of the blocked transistor up to its threshold voltage (phenomenon A), or the reduction of the gate voltage of the transistor passing below its threshold voltage (phenomenon B).

The oscillator of FIG. 3 comprises elements common to the oscillator of FIG. 2. Only the differences between the two oscillators are detailed below.

In the oscillator of FIG. 3, the resistor Rgl has been eliminated and replaced by an assembly of two parallel branches each connecting the gate of the transistor Ml to the drain of the transistor Ml. The first branch comprises a resistor Rgla and a diode Dla connected in series, and the second branch comprises a resistor Rglb and a diode Dlb connected in series. The diode Dla of the first branch is mounted directly between the gate and the drain of the transistor Ml, that is to say that the current can flow in the first branch only from the gate to the drain of the transistor Ml, and the diode Dlb of the second branch is mounted in reverse between the gate and the drain of the transistor Ml, that is to say that the current can only flow in the second branch from the drain to the gate of the transistor Ml. In the example shown, the resistance Rgla has a first end

B15362 - DD17349ST connected to the gate of transistor Ml and a second end connected to the anode of diode Dla, and the cathode of diode Dla is connected to the drain of transistor Ml. Furthermore, in this example, the resistor Rglb has a first end connected to the drain of the transistor Ml and a second end connected to the anode of the diode Dlb, and the cathode of the diode Dlb is connected to the gate of the transistor Ml.

Similarly, in the oscillator of FIG. 3, the resistance Rg2 has been eliminated and replaced by an assembly of two parallel branches each connecting the gate of the transistor M2 to the drain of the transistor M2. The first branch comprises a resistor Rg2a and a diode D2a connected in series, and the second branch comprises a resistor Rg2b and a diode D2b connected in series. The diode D2a of the first branch is mounted directly between the gate and the drain of the transistor M2, that is to say that the current can flow in the first branch only from the gate to the drain of the transistor M2, and the diode D2b of the second branch is mounted in reverse between the gate and the drain of the transistor M2, that is to say that the current can flow in the second branch only from the drain to the gate of the transistor M2. In the example shown, the resistor Rg2a has a first end connected to the gate of the transistor M2 and a second end connected to the anode of the diode D2a, and the cathode of the diode D2a is connected to the drain of the transistor M2. Furthermore, in this example, the resistor Rg2b has a first end connected to the drain of the transistor M2 and a second end connected to the anode of the diode D2b, and the cathode of the diode D2b is connected to the gate of the transistor M2.

When the transistors Ml and M2 are respectively open and closed, a current flows in the capacitor Cl, passing through the resistor Rglb and through the diode Dlb, and a current flows in the capacitor C2, passing through the resistor Rg2a and through the diode D2a . When the transistors Ml and M2 are respectively closed and open, a current flows in the capacitor Cl, passing through the resistor Rgla and through the diode

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Dla, and a current flows in the capacitor C2, passing through the resistor Rg2b and through the diode D2b.

The resistors Rglb and Rg2a on the one hand, and Rgla and Rg2b on the other hand, preferably have different values, so as to favor one or the other of the two above-mentioned switching phenomena. The values of the resistances Rgla and Rg2a on the one hand, and Rglb and Rg2b on the other hand, are for example substantially identical to ensure the conduction times of the transistors Ml and M2 substantially identical (in the case where the capacitors Cl and C2 have substantially identical capacities).

Figure 4 is an electrical diagram illustrating another alternative embodiment of the oscillator of Figure 2, to promote one or the other of the two causes of switching A and B above.

The oscillator of Figure 4 includes the same elements as the oscillator of Figure 2, arranged in substantially the same manner, and further comprises a diode DI connected in series with the resistance Rgl between the gate and the drain of the transistor Ml , and a diode D2 connected in series with the resistor Rg2 between the gate and the drain of the transistor M2. The diode DI is mounted directly between the gate and the drain of the transistor Ml, that is to say that the current can only flow in the resistor Rgl from the gate to the drain of the transistor Ml. Similarly, the diode D2 is mounted directly between the gate and the drain of the transistor M2, that is to say that the current can flow in the resistor Rg2 only from the gate to the drain of the transistor M2. More particularly, in the example shown, the resistor Rgl has a first end connected to the gate of the transistor Ml and a second end connected to the anode of the diode Dl, and the cathode of the diode DI is connected to the drain of the transistor ml. Furthermore, in this example, the resistor Rg2 has a first end connected to the gate of the transistor M2 and a second end connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the drain of the transistor M2.

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The oscillator of FIG. 4 further comprises a resistor Rgl 'connecting the gate of the transistor Ml to the node V +, and a resistor Rg2' connecting the gate of the transistor M2 to the node V +. More particularly, in the example of FIG. 4, the resistor Rgl 'has a first end connected to the gate of the transistor Ml and a second end connected to the node V +, and the resistor Rg2' has a first end connected to the gate of the transistor M2 and a second end connected to node V +.

When the transistors Ml and M2 are respectively open and closed, a current flows in the capacitor Cl, coming from the resistor Rgl ', and a current flows in the capacitor C2, passing through the resistor Rg2 and through the diode D2. When the transistors Ml and M2 are respectively closed and open, a current flows in the capacitor Cl, passing through the resistor Rgl and through the diode Dl, and a current flows in the capacitor C2, coming from the resistor Rg2 '.

The choice of the resistance values Rgl, Rgl ', Rg2 and Rg2' makes it possible to favor one or the other of the two above-mentioned switching phenomena. For example, the resistances Rgl 'and Rg2 on the one hand, and Rg2' and Rgl on the other hand, have different values so as to favor one or the other of the two switching phenomena, and the resistors Rgl and Rg2 on the one hand, and Rgl 'and Rg2' on the other hand, have substantially identical values to ensure conduction times of the transistors Ml and M2 substantially identical (considering capacitors Cl and C2 of substantially the same capacity and by considering the values of the resistances Rdl and Rd2 negligible compared to the values of the resistances Rgl, Rgl ', Rg2 and Rg2'.

As a variant (not shown), the resistors Rgl 'and Rg2' connect the gates of the transistors Ml and M2 not to the node V +, but to a node of application of a fixed positive bias potential different from the potential of the node V +.

In the examples of Figures 2, 3 and 4, the resistors Rdl and Rd2 can be replaced by any other type of load

B15362 - DD17349ST intended to be supplied by an oscillating signal, for example inductors, as illustrated for example in Figures 5 and 6.

FIG. 5 is an electrical diagram of an exemplary embodiment of a DC-DC converter with galvanic isolation, comprising an oscillator of the type described in relation to FIG. 2.

The oscillator of the DC / DC converter in Figure 5 differs from the oscillator in Figure 2 in that, in the example in Figure 5, the resistors Rdl and Rd2 have been replaced by a conductive winding Wp at mid point , forming the primary winding of a transformer T. In the example shown, the winding Wp has a first end connected to the drain of the transistor Ml and a second end connected to the drain of the transistor M2, the midpoint of the winding Wp being connected to the top supply node V + via an inductor L. More particularly, the inductor L has a first end connected to the midpoint of the winding Wp and a second end connected to the node V +. In this example, the nodes V + and V- are the nodes for applying the input voltage of the DC / DC converter. In FIG. 5, a voltage source is shown providing a DC voltage Valim between the nodes V + and V-.

The converter of FIG. 5 further comprises a secondary stage comprising a conductive winding Ws magnetically coupled to the primary winding Wp, and forming the secondary winding of the transformer T. In the example shown, the ends of the secondary winding Ws are connected to input nodes of an AC / DC conversion stage 51 (not detailed) suitable for rectifying and converting into a DC voltage supplied at the terminals of an Cout output capacitor, the alternating voltage supplied by the secondary winding Ws. In this example, the electrodes of the Cout capacitor correspond to the nodes for supplying the output voltage of the DC / DC converter.

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FIG. 6 is an electrical diagram of another exemplary embodiment of a DC-DC converter with galvanic isolation, comprising an oscillator of the type described in relation to FIG. 2.

The converter of FIG. 6 differs from the converter of FIG. 5 in that, in the example of FIG. 6, the primary winding Wp of the transformer T is a winding without a midpoint. In the example shown, the primary winding Wp has a first end connected to the drain of the transistor Ml and a second end connected to the drain of the transistor M2. As a variant, a capacitor (not shown) can be placed in series with the winding Wp between the drains of the transistors Ml and M2, for example between the drain of the transistor Ml and the first end of the winding Wp, to avoid the saturation of the transformer T in the case where the conduction times of the transistors Ml and M2 are not strictly identical.

The inductance L of the converter of FIG. 5 is deleted, and the converter of FIG. 6 instead includes an inductance L1 connecting the drain of the transistor Ml to the node V +, and an inductance L2 connecting the drain of the transistor M2 to the node V + . More particularly, in the example shown, the inductor L1 has a first end connected to the drain of the transistor Ml and a second end connected to the node V +, and the inductor L2 has a first end connected to the drain of the transistor M2 and a second end connected to the V + node. By way of example, the inductors L1 and L2 are substantially of the same values.

An advantage of the DC / DC converters of FIGS. 5 and 6 resides in the fact that the assembly is self-oscillating, and therefore does not require an external circuit for controlling the transistors Ml and M2.

The variant embodiments of the oscillator of FIG. 2, illustrated in FIGS. 3 and 4, can be applied to the converters of FIGS. 5 and 6.

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Furthermore, in the variant of FIG. 5, the inductance L can be of zero value or close to zero. An additional inductor (not shown) can be placed between the AC / DC conversion circuit 51 (for example a diode bridge) and the Cout capacitor.

More generally, oscillators of the type described in relation to FIGS. 2, 3 and 4, can be used in any type of circuit capable of taking advantage of a self-oscillating mounting of two MOS transistors mounted in parallel and sharing a common node (the source node in the examples shown).

FIG. 7 is an electrical diagram of another alternative embodiment of the oscillator of FIG. 2, which can be used when the supply voltage of the oscillator is greater than the voltages which can be supported without degradation by the gates of the transistors MOS Ml and M2.

The assembly of FIG. 7 is a cascode assembly comprising the same elements as the assembly of FIG. 2, arranged in substantially the same manner, and further comprising an MOS transistor Ml 'connected in series with the transistor Ml, between the transistor Ml and the node V +, and a MOS transistor M2 'connected in series with the transistor M2, between the transistor M2 and the node V +. The transistors Ml 'and M2' are for example of the same type of conductivity as the transistors Ml and M2 respectively, namely N-channel transistors in the example shown. In the example of FIG. 7, the transistor Ml 'has its source connected to the drain of the transistor Ml and its drain connected to the end of the resistance Rdl opposite the node V +, and the transistor M2' has its source connected to the drain of transistor M2 and its drain connected to the end of resistance Rd2 opposite to node V +. The gates of the transistors Ml 'and M2' are connected (connected in the example shown) to the same node B of application of a fixed bias potential λ / b. The oscillator of FIG. 7 further comprises a diode DC1 directly connecting the drain of the transistor Ml to the node B, and a diode DC2 directly connecting the drain of the

B15362 - DD17349ST transistor M2 at node B. More particularly, in the example shown, the anode and the cathode the diode DC1 are connected respectively to the drain of the transistor Ml and to the node B, and the anode and the cathode of the diode DC2 are connected respectively to the drain of transistor M2 and to node B.

The transistors Ml 'and M2' are dimensioned to be able to withstand without degradation the maximum voltage seen by the oscillator. By way of example, in assemblies of the type described in relation to FIGS. 5 and 6, the transistors Ml 'and M2' will be dimensioned to support at least twice the input voltage Valim of the circuit. The fixed bias voltage Vb is chosen to be greater than the threshold voltage of the transistors Ml 'and M2', for example of the order of 12 to 15 V for transistors having a threshold voltage of the order of 3 V. When the transistor M2 conducts, the source of the transistor M2 'is at a voltage close to 0 V. The transistor M2' then sees a gate-source voltage greater than its threshold voltage, and is therefore conductive. Conversely, when the transistor M2 turns off, its drain voltage rises to a value substantially equal to the fixed bias voltage applied to the node B. The transistor M2 'then sees a gate-source voltage lower than its voltage threshold, which results in its blocking. Similarly, when the transistor Ml conducts, the source of the transistor Ml 'is at a voltage close to 0 V. The transistor Ml' then sees a gate-source voltage greater than its threshold voltage, and is therefore conductive. Conversely, when the transistor M1 is blocked, its drain voltage rises to a value substantially equal to the fixed bias voltage applied to the node B. The transistor Ml 'then sees a gate source voltage lower than its threshold voltage, which results in its blocking. Thus, the transistors Ml and M2 respectively control the transistors Ml 'and M2' by their sources, so that the transistor Ml 'is open when the transistor Ml is open and closed when the transistor Ml is closed, and that the transistor M2' either open when transistor M2 is open and closed

B15362 - DD17349ST when transistor M2 is closed. The diodes DC1 and DC2 make it possible to clip the drain voltages of the transistors Ml and M2, so that the latter do not exceed a value substantially equal to the bias voltage Vb applied to the node B.

The variant embodiments of the oscillator of FIG. 2, illustrated in FIGS. 3 and 4, can be applied to the oscillator of FIG. 7.

The oscillator of FIG. 7 can also be used in assemblies of the type described in relation to FIGS. 5 and 6.

FIG. 8 more particularly illustrates an embodiment of a DC / DC converter of the type described in relation to FIG. 5, comprising an oscillator of the type described in relation to FIG. 7.

The converter of Figure 8 includes the same elements as the converter of Figure 5, arranged in substantially the same manner as in the example of Figure 5, and further comprises, as in the example of Figure 7, two MOS transistors Ml 'and M2' and two clipping diodes DC1 and DC2. In the example of FIG. 8, the transistor Ml 'has its source connected to the drain of the transistor Ml and its drain connected to the first end of the primary winding Wp, and the transistor M2' has its source connected to the drain of the transistor M2 and its drain connected to the second end of the primary winding Wp. The gates of the transistors Ml 'and M2' are connected to the same node B of application of a fixed bias potential Vb. The diode DC1 directly connects the drain of the transistor Ml to the node B, and the diode DC2 directly connects the drain of the transistor M2 to the node B.

More generally, an oscillator of the type described in relation to FIG. 7 can be used in any type of circuit capable of taking advantage of a self-oscillating assembly of two MOS transistors mounted in parallel and sharing a common node (the source node in the examples shown). By way of example, an oscillator of the type described in relation to the

B15362 - DD17349ST Figure 7 can advantageously be used in isolated DC / DC conversion circuits of the type described in French patent application N ° 16/57256 filed by the applicant on July 28, 2016 and the content of which is here incorporated by reference in the conditions authorized by law. This patent application describes in particular a converter adapted to ensure the transformation, with isolation, of a primary voltage into a secondary voltage, this converter comprising:

a primary stage connected to first and second nodes for applying the primary voltage and comprising:

a first winding having a first end connected to the first node;

a primary parallel resonant circuit connected to a second end of the first winding;

a second winding mounted in parallel with the primary parallel resonant circuit and forming the primary of a first transformer; and first and second primary switches each mounted in series with an output branch of the primary parallel resonant circuit and connecting said output branch to the second node (B),

- And a secondary stage connected to third and fourth nodes for supplying the secondary voltage and comprising:

a third winding having a first end connected to the third node; and a fourth winding connected to a second end of the third winding and forming the secondary of the first transformer, in which the first primary switch comprises first and second transistors connected in series, and the second primary switch comprises third and fourth transistors connected in series , the gates of the first and third transistors being connected to the same node for applying a first DC bias voltage, the gate of the second

B15362 - DD17349ST transistor being connected to the midpoint between the third and fourth transistors, and the gate of the fourth transistor being connected to the midpoint between the first and second transistors.

In such a converter, in accordance with what has been described above in relation to FIGS. 2 to 7, first and second resistors can be added to connect the gate of the second transistor to the drain of the second transistor, respectively, and the gate of the fourth transistor to the drain of the fourth transistor. In addition, in accordance with what has been described above in relation to FIGS. 2 to 7, the connection between the gate of the second transistor and the drain of the fourth transistor may include a first capacitor, and the connection between the gate of the fourth transistor and the drain of the second transistor may include a second capacitor.

FIG. 9 is an electrical diagram illustrating an example of an electronic oscillator produced on the basis of MOS transistors according to a second embodiment.

Unlike the first embodiment in which two self-controlled MOS transistors in phase opposition are connected in parallel, in the second embodiment, the oscillator comprises two self-controlled MOS transistors in phase opposition connected in series. In the second embodiment, transformers are used to transfer a voltage representative of the drain-source voltage of the first transistor between the gate and the source of the second transistor, and to transfer a voltage representative of the drainsource voltage of the second transistor between the gate and the source of the first transistor.

FIG. 9 more particularly illustrates an embodiment of a self-controlled capacitive half-bridge using an oscillator according to the second embodiment to apply the supply half-voltage of the circuit alternately with positive polarity and with negative polarity across a transformer winding. In

B15362 - DD17349ST In this example, each of the two half-bridge switches is formed by a cascode arrangement of two MOS transistors connected in series.

The circuit of FIG. 9 comprises two N-channel MOS transistors Ml and M2, for example identical to the manufacturing dispersions, connected in series between nodes V + and V of application of a continuous supply voltage Valim (not referenced on Figure 9) of the circuit. In this example, the circuit also comprises two N-channel MOS transistors Ml 'and M2', for example identical to the manufacturing dispersions, connected respectively in series with the transistor Ml between the transistor Ml and the node V +, and in series with the transistor M2 between the transistor M2 and the transistor Ml. More particularly, in the example shown, the transistor Ml has its source connected to a node C and its drain connected to the source of the transistor Ml ', and the transistor Ml' has its drain connected to the node V +. In addition, the transistor M2 has its source connected to the node V- and its drain connected to the source of the transistor M2 ', and the transistor M2' has its drain connected to the node C.

The circuit of FIG. 9 further comprises a resistor Rgl connecting the gate of the transistor Ml to the drain of the transistor Ml, and a resistor Rg2 connecting the gate of the transistor M2 to the drain of the transistor M2. More particularly, in the example of FIG. 9, the resistor Rgl has a first end connected to the gate of the transistor Ml and a second end connected to the drain of the transistor Ml, and the resistor Rg2 has a first end connected to the gate of the transistor M2 and a second end connected to the drain of transistor M2.

The circuit of FIG. 9 further comprises a capacitor C1 connecting the gate of the transistor Ml to a node Gl, and a capacitor C2 connecting the gate of the transistor M2 to a node G2. More particularly, in the example shown, the capacitor Cl has a first electrode connected to the gate of the transistor Ml and a second electrode connected to the node Gl, and the capacitor C2 has a first electrode connected to the gate of the transistor M2 and a second electrode connected to node G2.

B15362 - DD17349ST

The circuit of FIG. 9 further comprises a node SI connected to the source of the transistor Ml, and a node S2 connected to the source of the transistor M2.

The gate of the transistor Ml 'is connected (connected in the example shown), to a node D of application of a polarization potential Vbl fixed positive with respect to the potential of the node SI. In addition, the gate of transistor M2 'is connected (connected in the example shown) to a node E of application of a fixed bias potential Vb2 positive relative to the potential of node S2. The circuit of FIG. 9 further comprises a diode DC1 directly connecting the drain of the transistor Ml to the node D, and a diode DC2 directly connecting the drain of the transistor M2 to the node E. More particularly, in the example shown, l the anode and the cathode the diode DC1 are connected respectively to the drain of the transistor Ml and to the node D, and the anode and the cathode of the diode DC2 are respectively connected to the drain of the transistor M2 and to the node E.

The fixed bias voltage Vbl (referenced with respect to the node SI) is chosen to be greater than the threshold voltage of the transistor Ml ', for example of the order of 12 to 15 V for a transistor having a threshold voltage of the order of 3 V, and the fixed bias voltage Vb2 (referenced relative to node S2) is chosen to be greater than the threshold voltage of transistor M2 ', for example of the order of 12 to 15 V for a transistor having a voltage of threshold of the order of 3 V.

FIG. 9 shows an example of a circuit for generating the bias voltage Vbl, and an example of a circuit for generating the bias voltage Vb2. The bias voltage generation circuit Vbl comprises a resistor RI and a Zener diode ZI connected in series between the drain of the transistor Ml 'and the node SI. More particularly, in the example shown, the resistor RI has a first end connected to the node V + and a second end connected to the cathode of the Zener diode Zl, and the anode of the Zener diode Zl is connected to the node SI. Node D is connected

B15362 - DD17349ST at the cathode of the Zener Zl diode. Similarly, the circuit for generating the bias voltage Vb2 comprises a resistor R2 and a Zener diode Z2 connected in series between the drain of the transistor M2 'and the node S2. More particularly, in the example shown, the resistor R2 has a first end connected to the node V + and a second end connected to the cathode of the Zener diode Z2, and the anode of the Zener diode Z2 is connected to the node S2. The node E is connected to the cathode of the Zener diode Z2.

Thus, the DC bias voltage Vbl applied to the node D and referenced with respect to the node SI is substantially equal to the avalanche voltage of the Zener diode Zl, and the DC bias voltage Vb2 applied to the node E and referenced with respect to at node S2 is substantially equal to the avalanche voltage of the Zener diode Z2.

The circuit of FIG. 9 further comprises a decoupling capacitor Cl 'and a transformer tl connecting the drain and source nodes of the transistor Ml respectively to the nodes G2 and S2, as well as a decoupling capacitor C2' and a transformer t2 connecting the drain and source nodes of transistor M2 respectively to nodes G1 and SI. More particularly, in the example shown, the transformer tl comprises a primary conductor winding wpl, a first end of which is connected to the node SI and the second end of which is connected to a first electrode of the capacitor Cl ', the second electrode of the capacitor Cl' being connected to the drain of the transistor Ml. The transformer tl further comprises a secondary conductive winding wsl magnetically coupled to the primary winding wpl, the secondary winding wsl having a first end connected to the node S2 and a second end connected to the node G2. Similarly, the transformer t2 comprises a primary conductive winding wp2, a first end of which is connected to the node S2 and the second end of which is connected to a first electrode of the capacitor C2 ', the second electrode of the capacitor C2' being

B15362 - DD17349ST connected to the drain of transistor M2. The transformer t2 further comprises a secondary conductive winding ws2 magnetically coupled to the primary winding wp2, the secondary winding ws2 having a first end connected to the node SI and a second end connected to the node G1.

The circuit of FIG. 9 further comprises, in parallel with the series association of the transistors Ml ', Ml, M2' and M2, a series association of two capacitors Caliml and Calim2. In the example shown, the capacitor Caliml has a first electrode connected to the node V + and a second electrode connected to a node F, and the capacitor Calim2 has a first electrode connected to the node F and a second electrode connected to the node V-.

The circuit of FIG. 9 also comprises a transformer T comprising a primary conductive winding Wp magnetically coupled to a secondary conductive winding Ws. The primary winding Wp of the transformer T has a first end connected to the node C and a second end connected to the node F. The secondary winding Ws of the transformer T can be connected to any circuit capable of exploiting the alternating voltage transmitted by the transformer T, for example an AC / DC conversion stage of the type described in relation to FIG. 5.

The operation of the MOS transistor oscillator of the circuit of FIG. 9 is similar to what has been described previously in relation to FIG. 2, with the difference that the drain-source voltage of the transistor Ml (respectively M2) is applied between the electrode of the capacitor C2 (respectively Cl) opposite the gate of the transistor M2 (respectively Ml) and the source of the transistor M2 (respectively Ml), not by a direct electrical connection as in the example of FIG. 2, but via a decoupling capacitor Cl '(respectively C2') and a transformer tl (respectively t2).

B15362 - DD17349ST

In operation, the capacitors Caliml and Calim2 each charge at a voltage substantially equal to half of the supply voltage Valim applied between the nodes V + and V-. When the switch formed by the transistors Ml and Ml 'is closed (on) and when the switch formed by the transistors M2 and M2' is open (blocked), the voltage + Valim / 2 is applied by the capacitor Caliml to the terminals of the primary winding Wp of the transformer, between nodes F and C. When the switch formed by the transistors Ml and Ml 'is open (blocked) and when the switch formed by the transistors M2 and M2' is closed (passing ), the voltage -Valim / 2 is applied by the capacitor Calim2 at the terminals of the primary winding Wp of the transformer, between nodes F and C. An alternating voltage is thus supplied by the transformer T at the terminals of the secondary winding Ws .

As a variant, two arms of the type described in relation to FIG. 9, operating in phase opposition, can be used to make a complete capacitive bridge assembly.

More generally, an oscillator of the type described in relation to FIG. 9 can be used in any assembly capable of taking advantage of a self-oscillating switching in phase opposition of two MOS switches connected in series.

Furthermore, in the oscillator of FIG. 9, the transistors Ml 'and M2' are optional. In particular, if the level of the supply voltage is sufficiently low compared to the maximum voltage which the transistors Ml and M2 can withstand without degradation, the transistors Ml 'and M2' can be omitted. In this case, the transistors Ml and M2 are directly connected in series between the nodes V + and V-, and the elements RI, Zl, DC1, R2, Z2, DC2 can be omitted.

In addition, the variant embodiments described in relation to FIGS. 3 and 4 can be adapted to an oscillator of the type described in relation to FIG. 9.

Particular embodiments have been described. Various variants and modifications will appear to the man of

B15362 - DD17349ST art. In particular, although only examples of embodiments of oscillators based on N-channel MOS transistors have been described, those skilled in the art will be able to adapt the lessons of the present application to produce electronic oscillators based on 5 P channel MOS transistors

Claims (12)

1. Electronic oscillator comprising: first (Ml) and second (M2) MOS transistors; a first capacitor (Cl) of which a first electrode is connected to the gate of the first transistor (Ml), and a second capacitor (C2) of which a first electrode is connected to the gate of the second transistor (M2); a first resistor (Rgl; Rgla) connecting the first electrode of the first capacitor (Cl) to the drain of the first transistor (Ml), and a second resistor (Rg2; Rg2a) connecting the first electrode of the second capacitor (C2) to the drain of the second transistor (M2); and a cross-link circuit adapted to apply, between a second electrode of the first capacitor (Cl) and the source of the first transistor (Ml), a voltage representative of the drain-source voltage of the second transistor (M2), and, between a second electrode of the second capacitor (C2) and the source of the second transistor (M2), a voltage representative of the drain-source voltage of the first transistor (Ml). 2. Oscillator according to claim 1, in which the cross link circuit comprises a direct connection between the source of the first transistor (Ml) and the source of the second transistor (M2), a direct connection between the second electrode of the first capacitor (Cl ) and the drain of the second transistor (M2), and a direct connection between the second electrode of the second capacitor (C2) and the drain of the first transistor (Ml). 3. Oscillator according to claim 2, comprising first (V-) and second (V +) nodes for applying a DC supply voltage, the sources of the first (Ml) and second (M2) transistors being connected to the first node (V-), the drain of the first transistor (Ml) being connected to the second node (V +) via a first load (Rdl; Wp, L; Ll), and the drain of the second transistor (M2) being connected to the second node (V +) via a second load (Rd2; Wp, L; L2). B15362 - DD17349ST 4. Oscillator according to claim 3, in which the first (Rdl) and second (Rd2) charges are of the loads resistive. 5. Oscillator according to claim 3, in which the first (Wp, L; Ll) and second (Wp, L; L2) charges are inductive loads. 6. Oscillator according to claim 5, comprising a transformer (T) comprising a primary winding (Wp) having a first end connected to the drain of the first transistor (Ml) and a second end connected to the drain of the second transistor (M2), and a secondary winding (Ws) magnetically coupled to the primary winding (Wp). 7. An oscillator according to claim 6, in which the primary winding (Wp) comprises a midpoint connected to the second node (V +) via an inductor (L). 8. An oscillator according to claim 6, in which the primary winding (Wp) does not have a midpoint, a first end of the primary winding (Wp) being connected to the second node (V +) via a first inductor (L1) and a second end of the primary winding (Wp) being connected to the second node (V +) via a second inductor (L2). 9. Oscillator according to any one of claims 3 to 8, further comprising a third MOS transistor (Ml ') connected in series with the first transistor (Ml), between the drain of the first transistor (Ml) and the second node ( V +), and a fourth MOS transistor (M2 ') connected in series with the first transistor (M2), between the drain of the second transistor (M2) and the second node (V +), the gates of the third (Ml') and fourth (M2 ') transistors being connected to the same node for applying a fixed bias potential. 10. An oscillator according to claim 9, in which the first (Ml) and second (M2) MOS transistors are connected in series, the cross-link circuit comprising: B15362 - DD17349ST a third capacitor (Cl ') and a first transformer (tl) adapted to apply, between the second electrode of the second capacitor (C2) and the source of the second transistor (M2), a voltage representative of the drainsource voltage of the first transistor (Ml); and a fourth capacitor (C2 ') and a second transformer (t2) adapted to apply, between the second electrode of the first capacitor (Cl) and the source of the first transistor (Ml), a voltage representative of the drainsource voltage of the second transistor ( M2). 11. An oscillator according to claim 10, in which: the first transformer (tl) comprises a first primary winding (wpl) and a first secondary winding (wsl) magnetically coupled; the second transformer (t2) comprises a second primary winding (wp2) and a second secondary winding (ws2) magnetically coupled; the third capacitor (Cl ') has a first electrode connected to the drain of the first transistor (Ml) and a second electrode connected to a first end of the first primary winding (wpl), the second end of the first primary winding (wpl) being connected to the source of the first transistor (Ml); the fourth capacitor (C2 ') has a first electrode connected to the drain of the second transistor (M2) and a second electrode connected to a first end of the second primary winding (wp2), the second end of the second primary winding (wp2) being connected to the source of the second transistor (M2); the first secondary winding (wsl) has a first end connected to the second electrode of the second capacitor (C2) and a second end connected to the source of the second transistor (M2); and the second secondary winding (ws2) has a first end connected to the second electrode of the first capacitor B15362 - DD17349ST (Cl) and a second end connected to the source of the first transistor (Ml). 12. An oscillator according to any one of claims 1 to 11, further comprising: a first diode (Dla; Dl) connected in series with the first resistor (Rgla; Rgl) between the gate and the drain of the first transistor (Ml), the first diode (Dla; Dl) being mounted directly between the gate and the drain of the first transistor (Ml); and a second diode (D2a; D2) connected in series with the second resistor (Rgla; Rgl) between the gate and the drain of the second transistor (M2), the second diode (D2a; D2) being mounted directly between the gate and the drain of the second transistor (M2). 13 Oscillator according to claim 12, further comprising: a third diode (Dlb) and a third resistor (Rglb) connected in series between the gate and the drain of the first transistor (Ml), in parallel with the series association of the first resistor (Rgla) and the first diode ( Dla), the third diode (Dlb) being mounted in reverse between the gate and the drain of the first transistor (Ml); and a fourth diode (D2b) and a fourth resistor (Rg2b) connected in series between the gate and the drain of the second transistor (M2), in parallel with the series association of the second resistor (Rg2a) and the second diode (D2a), the fourth diode (D2b) being mounted in reverse between the gate and the drain of the second transistor (M2). 14. The oscillator according to claim 12, further comprising a third resistor (Rgl ') connecting the gate of the first transistor (Ml) to a node for applying a fixed bias potential, and a fourth resistor (Rg2') connecting the gate of the second transistor (M2) at a node for applying a fixed bias potential.