SENSING CIRCUIT, CORRESPONDING AMPLIFIER, APPARATUS AND METHOD

Abstract

A switching amplifier, such as a Class D amplifier, includes a current sensing circuit. The current sensing circuit is formed by replica loop circuits that are selectively coupled to corresponding output inverter stages of the switching amplifier. The replica loop circuits operated to produce respective replica currents of the output currents generated by the output inverter stages. A sensing circuitry is coupled to receive the replica currents from the replica loop circuits and operates to produce an output sensing signal as a function of the respective replica currents.

Claims

1. A circuit, comprising: replica loop circuits selectively coupled to corresponding output inverter stages of a switching amplifier that generates amplifier output currents, wherein the replica loop circuits are configured to produce respective replica currents of the amplifier output currents; and a voltage-to-current converter circuit having inputs configured to receive a reference voltage and a first replica current of the respective replica currents of the amplifier output currents and an output coupled to receive a second replica current of the respective replica currents of the amplifier output currents and produce an output sensing signal as a function of the respective replica currents.

2. The circuit of claim 1, wherein the voltage-to-current converter circuit comprises: an amplifier having a first input coupled to receive the reference voltage, a second input coupled to receive the first replica current, and an output; a feedback resistor coupled between the second input and the output of the amplifier; and an output resistor coupled between the output of the amplifier and the output of the voltage-to-current converter.

3. The circuit of claim 1, further comprising an output buffer having an input coupled to receive the output sensing signal, said output buffer configured to buffer a voltage of the output sensing signal to produce a buffered sensing signal.

4. The circuit of claim 1, wherein the replica loop circuits include current mirror circuits configured to providing the replica currents.

5. The circuit of claim 4, wherein the current mirror circuits include corresponding down-scaling current mirror circuits configured to provide respective scaled-down replica currents.

6. The circuit of claim 1, further comprising, for each replica loop circuit, a switching circuit configured to selectively couple the replica loop circuit to the corresponding output inverter stage.

7. The circuit of claim 6, further comprising means for actuating the switching circuit whose corresponding output inverter stage is driven with a smaller duty-cycle.

8. The circuit of claim 1, wherein each replica loop circuit comprises: a transistor configured to produce the respective replica current; a loop amplifier having a first input coupled to the corresponding output inverter stage, a second input coupled to a conduction terminal of the transistor and an output coupled to a control terminal of the transistor.

9. The circuit of claim 8, wherein each replica loop circuit further includes an auto-zero circuit.

10. The circuit of claim 1, further comprising a sampling circuit having an input coupled to receive the output sensing signal, said sampling circuit configured to sample the output sensing signal at timed instants synchronized with a clock signal clocking operation of the switching amplifier.

11. The circuit of claim 10, wherein the sampling circuit is activated by a sampling timing signal having rising and falling edges, wherein the falling edges of the sampling timing signal synchronized with rising edges of the clock signal clocking operation of the switching amplifier.

12. The circuit of claim 10, wherein the sampled output sensing signal is indicative of a mean value of an output current from the switching amplifier.

13. A circuit, comprising: replica loop circuits selectively coupled to corresponding output inverter stages of a switching amplifier that generates amplifier output currents, wherein the replica loop circuits are configured to produce respective replica currents of the amplifier output currents; at least one sensing circuit coupled to receive from the replica loop circuits the respective replica currents, wherein the at least one sensing circuit is configured to produce an output sensing signal as a function of the respective replica currents output from the replica loop circuits; and switching circuitry to selectively couple the replica loop circuits to corresponding output inverter stages; wherein, in an operation of the output inverter stages to generate switched output currents having relatively higher and smaller duty-cycles, the switching circuitry is actuated to selectively couple the replica loop circuits to corresponding output inverter stages such that the replica loop circuit acts on the switched output current from the output inverter stage having a smaller duty-cycle.

14. The circuit of claim 13, wherein the at least one sensing circuit comprises a current-to-voltage converter circuit configured to convert the respective replica currents to a voltage output sensing signal.

15. The circuit of claim 14, wherein the at least one sensing circuit further includes an output buffer configured to buffer the voltage output sensing signal and produce a buffered sensing signal.

16. The circuit of claim 13, wherein the replica loop circuits include current mirror circuits configured to providing the replica currents.

17. The circuit of claim 16, wherein the current mirror circuits include corresponding down-scaling current mirror circuits configured to provide respective scaled-down replica currents.

18. The circuit of claim 13, wherein the replica loop circuits include corresponding loop amplifiers having an associated auto-zero circuitry.

19. The circuit of claim 13, further comprising a sampling circuit configured to sample the output sensing signal at timed instants synchronized with a clock signal clocking operation of the switching amplifier.

20. The circuit of claim 19, wherein the sampling circuit is activated by a sampling timing signal having rising and falling edges, wherein the falling edges of the sampling timing signal synchronized with rising edges of the clock signal clocking operation of the switching amplifier.

21. The circuit of claim 19, wherein the sampled output sensing signal is indicative of a mean value of an output current from the switching amplifier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] One or more embodiments will now be described, by way of example only, with reference to the annexed Figures wherein:

[0031] FIG. 1 is a block diagram illustrative of a possible context of use of embodiments,

[0032] FIG. 2 is a circuit diagram exemplary of embodiments,

[0033] FIGS. 3 and 4 are diagrams exemplary of possible operation of the circuit of FIG. 2,

[0034] FIG. 5 is further exemplary of the principles of operation exemplified in FIGS. 3 and 4,

[0035] FIG. 6 is a simplified circuit diagram exemplary of possible operation of embodiments,

[0036] FIGS. 7A through 7D are exemplary of possible timing in operation of embodiments,

[0037] FIGS. 8A through 8D are exemplary of another circuit representation exemplary of possible operation of embodiments,

[0038] FIG. 9 is a circuit diagram exemplary of possible features of embodiments,

[0039] FIGS. 10A through 10E are exemplary of possible timing in operation of embodiments,

[0040] FIG. 11 is a circuit diagram exemplary of possible features of embodiments, and

[0041] FIGS. 12A through 12E are exemplary of possible timing in operation of embodiments.

DETAILED DESCRIPTION

[0042] In the ensuing description, one or more specific details are illustrated, aimed at providing an in-depth understanding of examples of embodiments of this description. The embodiments may be obtained without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that certain aspects of embodiments will not be obscured.

[0043] Reference to an embodiment or one embodiment in the framework of the present description is intended to indicate that a particular configuration, structure, or characteristic described in relation to the embodiment is comprised in at least one embodiment. Hence, phrases such as in an embodiment or in one embodiment that may be present in one or more points of the present description do not necessarily refer to one and the same embodiment. Moreover, particular conformations, structures, or characteristics may be combined in any adequate way in one or more embodiments.

[0044] The references used herein are provided merely for convenience and hence do not define the extent of protection or the scope of the embodiments.

[0045] In FIG. 1, reference 100 indicates as a whole an arrangement including a switching amplifier 10 including outputs OUT.sub.H (high) and OUT.sub.L (low) supplying load current to a load R.sub.LOAD such as for example a resistive load.

[0046] The amplifier 10 may include, for example, a Class D Amplifier with an associated output filter (for example a pi low-pass filter) for example including two inductors LE and a capacitor C.sub.F with the inductors L.sub.F coupled at their proximal ends to the amplifier stage 10 to be traversed by the current from the outputs OUT.sub.H, OUT.sub.L and the capacitor C.sub.F coupled across the distal terminals of the inductors L.sub.F with the (low-pass) filtered signal applied to the load R.sub.LOAD.

[0047] The principles underlying operation of such a switching amplifier arrangement are known in the art, thus making it unnecessary to provide a more detailed description herein.

[0048] As noted, a Class D amplifier with quaternary modulation may be exemplary of such an application. A possible scenario of use of such an arrangement is a micromirror application wherein sensing the output current from the Class D amplifier makes it possible to sense spurious current components due to the physical behavior of the mirror. These currents may thus be compensated by means of a cancelling process to increase mirror driving accuracy.

[0049] Reference to that possible area of application is merely exemplary and not meant to be limiting of the scope of embodiments.

[0050] In various applications, operation of the amplifier 10 will involve sensing (for example measuring) the filtered output signal (current) from the amplifier 10 as exemplary of the current supplied to the load R.sub.LOAD through the external (for example LC) filter.

[0051] FIG. 1 is exemplary of performing such a sensing action via a sensing resistor R.sub.SENSE arranged in series with the load R.sub.LOAD, with the voltage drop V.sub.SENSEHV.sub.SENSEL across the resistor R.sub.SENSE indicative of the magnitude of the current supplied to the load R.sub.LOAD.

[0052] As noted, such an arrangement may undesirably involve the use of an external component such as the resistor R.sub.SENSE with an associated efficiency loss.

[0053] A general exemplary layout of one or more embodiments is shown in FIG. 2, where 10H and 10L indicate the output inverter stages of the switching amplifier 10 (not visible as a whole in FIG. 2).

[0054] The output nodes OUT.sub.H, OUT.sub.L of the inverter stages 10H, 10L provide output currents to be supplied to the load R.sub.LOAD via the filter L.sub.F, C.sub.F.

[0055] One or more embodiments may include replica loop circuits 12H, 12L to provide replicas (for example scaled-down replicas) I.sub.DMYH, I.sub.DMYL of the currents supplied towards the load R.sub.LOAD via the output nodes OUT.sub.H, OUT.sub.L of the amplifier 10.

[0056] In one or more embodiments, the replica loop circuits 12H, 12L may be integrated in the amplifier 10.

[0057] Reference 14 in FIG. 2 indicates a current-to-voltage converter sensitive to the replica currents I.sub.DMYH, I.sub.DMYL and configured for generating a corresponding output (voltage) signal V.sub.C which may be fed to an output buffer circuit 16 to produce an output sensing signal (for example a voltage signal) V.sub.SENSE.

[0058] In one or more embodiments the converter circuit 14 and/or the output buffer 16 may be integrated in the amplifier 10 as previously indicated for the replica loop circuits 12H, 12L.

[0059] In one or more embodiments, operation of the replica loop circuits 12H, 12L may be controlled (as schematically indicated by switches 20H, 20L in FIG. 2) in such a way that the replica loop circuits 12H, 12L may be rendered active on the switching (for example Class D) output inverter 10H, 10L having the smaller duty-cycle as conventionally contemplated for Class D operation.

[0060] This type of operation is exemplified in FIGS. 3 and 4 with reference to situations where: [0061] the duty-cycle at output node OUT.sub.L is higher than the duty-cycle at output node OUT.sub.H (FIG. 3), and [0062] the duty-cycle at output node OUT.sub.L is lower than the duty-cycle at output node OUT.sub.H (FIG. 4).

[0063] As used herein, higher and lower are intended to refer to relative duty-cycle values T.sub.ON/(T.sub.ON+T.sub.OFF) of the switched (for example PWM modulated) signals.

[0064] In one or more embodiments, the replica loop circuits 12H, 12L may include K:1 current mirrors including two transistors (for example NMOS transistors), namely: [0065] M.sub.OUTH and M.sub.SH (this latter providing I.sub.DMYH), and [0066] M.sub.OUTL and M.sub.SL (this latter providing I.sub.DMYL).

[0067] In the situation exemplified in FIG. 3, the load current I.sub.L flows from the output node OUT.sub.L to the node OUT.sub.H through the external LC filter so that (only) M.sub.OUTH is traversed by this current which is mirrored (and scaled down) by the replica loop circuit 12H.

[0068] The two transistors M.sub.OUTH and M.sub.SH in the K:1 current mirror have their control electrodes (gates in the case of a field effect transistors such as MOS transistors) in common and the replica loop includes a differential stage 22H which forces their, for example, drain nodes to be equal, thus providing current mirroring and scaling (by a factor K), so that I.sub.DMYH=I.sub.L/K.

[0069] The replica loop 12H being active is exemplified by the switch 20H being represented in a closed (that is conductive) condition.

[0070] In an arrangement as exemplified in the figures, the mirrored, scaled-down current flows through a feedback resistor R1 of an amplifier 140 included in the current/voltage converter 14.

[0071] In an arrangement as exemplified in the figures the amplifier 140 includes a differential stage receiving a (voltage) reference signal V.sub.REF at one of its inputs (for example non-inverting) with the feedback resistor R1 coupled to the replica loop circuit 12H at the other (for example inverting) input.

[0072] In an arrangement as exemplified in the figures, an output resistor R2 is set between the output of the differential stage 140 and the buffer stage 16 (and the loop replica circuit 12L).

[0073] The current flowing in the feedback resistor of the differential stage 140 of the converter 14 may be buffered at 16 to generate an output signal V.sub.SENSE=V.sub.REF+I.sub.DMYH*R1/K.

[0074] Operation in the complementary conditions as exemplified in FIG. 4 is essentially identical save that the two loop replica circuits 12H, 12L swap their roles with the loop 12L leading to the generation of a current I.sub.DMYL=I.sub.L/K which flows in the output resistor R2 of the amplifier 140 in the converter 14 and is buffered to generate a sensing signal V.sub.SENSE=V.sub.REFI.sub.DMYL*R2/K.

[0075] By combining the two sense paths the signal V.sub.SENSE provides a good replica of the load current(s) of the switching (for example Class D) amplifier as shown in the right-hand side of FIG. 5 (assuming for example R1=R2=R).

[0076] As discussed previously, the replica loops 12H, 12L may operate with the target of facilitating rendering the drains of the transistors M.sub.OUTH,L and M.sub.SH,L (where M.sub.OUTH,L indicates MOUTH and M.sub.OUTL, while M.sub.SH,L indicates M.sub.SH and M.sub.SL) equal.

[0077] However, it was observed that the transistors M.sub.OUTH,L may exhibit (very) small values for the on resistance R.sub.ON, this resulting in a correspondingly small value for V.sub.OUT even with relatively high load currents.

[0078] As a result, a correct operation of the replica loop circuit may be facilitated by the loop amplifiers 22H, 22L having an offset comparable or smaller than V.sub.OUT.

[0079] For that reason, one or more embodiments may adopt an amplifier auto-zero technique in order to achieve high accuracy.

[0080] FIG. 6 is exemplary of a possible implementation of a replica loop with auto-zero the representation of FIG. 6 applying to both replica loop circuits 12H, 12L including the loop amplifiers 22H, 22L.

[0081] The chronograms of FIGS. 7A through 7D are exemplary of the timing of operation of switches SWA_A, SWA_B and 24, 26, 28 in four working phases as represented in FIGS. 7A through 7D by a 1, 2, 3 and 4.

[0082] In the four diagrams of FIGS. 7A through 7D: [0083] the diagram of FIG. 7A is exemplary of the clock signal used for switching (Class D modulation), [0084] the diagrams in FIG. 7B (dashed line and solid line) are exemplary of the outputs of the two single-ended Class D nodes, with the replica branch 12H, 12L active only on the output node having the smaller duty-cycle as discussed previously in connection with FIGS. 3 and 4, [0085] the diagram in FIG. 7C is exemplary of the enable signal for the switch SWA_A causing the output voltage from the transistor M.sub.OUTH,L to be sampled on a capacitor CSeH_A, and [0086] the diagram in FIG. 7D is exemplary of the enable signal for the switch SWA_B causing the output voltage from the transistor M.sub.OUTH,L to be sampled on capacitor CSeH_B.

[0087] FIGS. 8A through 8D are exemplary of the various enable (switch ON, that is conductive) and non-enable (switch OFF, that is non-conductive) conditions of the various switches presented in FIG. 6 in the four phases 1, 2, 3, 4.

[0088] Briefly (in the following the suffixes H and L distinguishing the two replica loop circuits are dropped for simplicity, operation of two circuits being otherwise the same):

[0089] 1 (FIG. 8A): M.sub.OUT is ON.fwdarw.V.sub.OUT[n]=R.sub.ON*I.sub.L. V.sub.OUT[n] is sampled on C.sub.SeH.sub._.sub.A, whereas the amplifier is in Sensing Phase using V.sub.OUT[n3] (voltage sampled on C.sub.SeH.sub._.sub.B in 2 of the previous clock cycle) as the reference voltage.fwdarw.V.sub.DMY=V.sub.OUT[n3]V.sub.OS[n]+V.sub.OS[n1] and since V.sub.OS[n]=V.sub.OS[n1].fwdarw.V.sub.DMY=V.sub.OUT[n3].fwdarw.I.sub.DMY=I.sub.L/K.fwdarw.I.sub.DMY in this phase is directly proportional to I.sub.L and can be used to generate V.sub.SENSE.

[0090] 2 (FIG. 8B): M.sub.OUT is ON.fwdarw.V.sub.OUT[n]=R.sub.ON*I.sub.L. V.sub.OUT[n] is sampled on C.sub.SeH.sub._.sub.B, whereas the amplifier is in Autozero Phase using V.sub.OUT[n1] (voltage sampled on C.sub.SeH.sub._.sub.A in 1 of the same clock cycle) as the reference voltage.fwdarw.V.sub.DMY=V.sub.OUT[n1].fwdarw.V.sub.OS[n].fwdarw.I.sub.DMY=I.sub.L/K+V.sub.OS[n]/(K*R.sub.ON). The term V.sub.OS[n]/(K*R.sub.ON) represents an error, thus the I.sub.DMY current, during this phase, is not useful for generating V.sub.SENSE.

[0091] 3 (FIG. 8C): M.sub.OUT is OFF.fwdarw.Both SWA_A and SWA_B are open. The amplifier is in Autozero Phase using V.sub.OUT[n2] (voltage sampled on C.sub.SeH.sub._.sub.A in 1 of the same clock cycle) as the reference voltage.fwdarw.V.sub.DMY=V.sub.OUT[n2]V.sub.OS[n].fwdarw.I.sub.DMY=I.sub.L/K+V.sub.OS[n]/(K*R.sub.ON). The term V.sub.OS[n]/(K*R.sub.ON) represents an error, thus the I.sub.DMY current, during this phase, is not useful for generating V.sub.SENSE.

[0092] 4 (FIG. 8D): M.sub.OUT is OFF.fwdarw.Both SWA_A and SWA_B are open. The amplifier is in Sensing Phase using V.sub.OUT[n2] (voltage sampled on C.sub.SeH.sub._.sub.B in f2 of the same clock cycle) as the reference voltage.fwdarw.V.sub.DMY=V.sub.OUT[n2]V.sub.OS[n]+V.sub.OS[n1] and since V.sub.OS[n]=V.sub.OS[n1].fwdarw.V.sub.DMY=V.sub.OUT[n2].fwdarw.I.sub.DMY=I.sub.L/K.fwdarw.I.sub.DMY in this phase is directly proportional to I.sub.L and can be used to generate V.sub.SENSE.

[0093] After the replica current I.sub.DMY (that is I.sub.DMYH or I.sub.DMYL, respectively, as a function of the active replica loop circuit considered) is converted to voltage, the output from the converter 14 may be sampled during the phase 1, that is when this is (directly) proportional to I.sub.L and is exempt from error, thanks to offset cancellation thus facilitating buffering at 16 to drive a load.

[0094] In one or more embodiments such a sampling action can be implemented in the buffer circuit 16 as schematically illustrated in FIG. 9.

[0095] In FIG. 9 reference 160 indicates an input stage receiving the signal Vc from the converter circuit 14 and reference 162 indicates an output stage providing an output sensing signal V.sub.SENSE.

[0096] In FIG. 9 a sampling switch EN.sub.SeH 164 set between the input and output stages 160, 162 of the buffer circuit 16 is exemplary of a possible implementation of the sampled output buffer with the respective sampling timing signal EN.sub.S&H added to the diagrams of FIGS. 7A through 7D as shown in the lower portion of FIGS. 10A through 10E thus showing that the replica current may be effectively sampled at the end of the phase (1.

[0097] The foregoing discussion assumes that the mean value I.sub.L of the load current (for example a sinusoidal current if the input to the switching amplifier for example Class D input) is a sine wave.

[0098] In one or more embodiments, the load current designated I.sub.BRIDGE may have superimposed a ripple due to the way of working of a Class D amplifier.

[0099] An accurate sensing of the mean (average) load current is facilitated by such a current ripple being cancelled.

[0100] In one or more embodiments, deriving the falling edge of the sampling signal EN.sub.S&H signal from the rising edge of the clock used for Class D modulation (see for example the diagrams a) in FIGS. 7A through 7D and FIG. 9) may facilitate having the voltage sample at the end of EN.sub.S&H to correspond (exactly) to the mean load current I.sub.L.

[0101] In that way, the possibility exists of automatically filtering the ripple of the bridge current as exemplified in the diagrams of the FIGS. 12A through 12E designate: [0102] FIG. 12A: the clock signal used for Class D modulation V.sub.CK, [0103] FIGS. 12B and 12C: the outputs form the two output nodes of the Class D amplifier OUT.sub.H, OUT.sub.L, [0104] FIG. 12D: the sampling signal EN.sub.S&H, and [0105] FIG. 12E: a possible sawtooth behavior (deliberately emphasized for ease of understanding) of the ripple I.sub.BRIDGE with respect to the average value I.sub.L.

[0106] FIG. 12E exemplifies how sampling taking place as discussed previously makes it possible to automatically filter out such a ripple.

[0107] A circuit arrangement according to one or more embodiments may include: [0108] replica loop circuits (for example 12H, 12L) couplable to output inverter stages (for example 10H, 10L) of a switching amplifier (for example 10) producing amplifier output currents, the replica loop circuits configured for producing respective replicas (for example I.sub.DMYH, I.sub.DMYL) of the output currents from the output inverter stages, and [0109] at least one sensing circuit (for example 14, 16) coupled to the replica loop circuits to receive therefrom the respective output current replicas, the sensing circuit configured to produce an output sensing signal (for example V.sub.SENSE) as a function of the respective output current replicas from the replica loop circuits.

[0110] In one or more embodiments the at least one sensing circuit may include a current-to-voltage converter circuit (for example 14) configured for converting the respective output current replicas to a voltage output sensing signal.

[0111] In one or more embodiments the at least one sensing circuit may include an output buffer (for example 16) configured for buffering the voltage signal and producing therefrom a buffered sensing signal (for example V.sub.SENSE).

[0112] In one or more embodiments, the replica loop circuits may include current mirrors (for example M.sub.OUTH, M.sub.SH; M.sub.OUTL, M.sub.SL) providing replicas of the output currents.

[0113] In one or more embodiments, the current mirrors may include down-scaling current mirrors provide respective scaled-down replicas of the output currents.

[0114] In one or more embodiments, with the output inverter stages generating switched output currents having relatively higher and smaller duty-cycles, the replica loop circuits may be selectively activatable (for example 20H, 20L) to act on the switched output current from the inverter stages having a smaller duty-cycle.

[0115] In one or more embodiments, the replica loop circuits may include loop amplifiers (for example 22H, 22L) having associated auto-zero circuitry (for example SWA_A, SWA_B, CSeH_A, CSeH_B, 24, 26, 28).

[0116] One or more embodiments may include a sampling circuit (for example 164) activatable to sample the output sensing signal at timed instants synchronized (for example EN.sub.S&H) with a clock signal (for example V.sub.CK) clocking operation of the switching amplifier.

[0117] One or more embodiments may include a sampling circuit activatable by a sampling timing signal having rising and falling edges, the falling edges of the sampling timing signal synchronized with the rising edges of the clock signal clocking operation of the switching amplifier (10), whereby the sampled output sensing signal is indicative of the mean value of the output current from the amplifier.

[0118] One or more embodiments may include a switching amplifier (for example a Class D amplifier) including output inverter stages producing amplifier output currents, the amplifier including a circuit arrangement according to one or more embodiments.

[0119] Apparatus according to one or more embodiments may include a switching amplifier according to one or more embodiments.

[0120] A method according to one or more embodiments may include: [0121] providing a switching amplifier having output inverter stages producing amplifier output currents, [0122] coupling to the output inverter stages of the switching amplifier replica loop circuits producing respective replicas of the output currents, and [0123] coupling to the replica loop circuits at least one sensing circuit receiving from the replica loop circuits respective output current replicas, [0124] producing via the sensing circuit an output sensing signal as a function of the respective output current replicas.

[0125] Without prejudice to the underlying principles, the details and embodiments may vary, even significantly, with respect to what has been described by way of example only, without departing from the extent of protection.

[0126] The extent of protection is defined by the annexed claims.