JP2005057573A - Signal reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal reproducing device provided with a boot strap circuit part which can securely drive a high side transistor T1 to "ON" irrespective of pulse width. <P>SOLUTION: The device is provided with a totem-pole type amplification part 30 composed of the high side transistor T1 and a low side transistor T2, which are composed of switching transistors, and the boost strap circuit part 21 composed of a diode D1 and two capacitors C1 and C2. Thus, driving voltage of the stable high side transistor T1 can be secured by a charge charged by the capacitor of small capacity in the case of short pulse width with which the low side transistor T2 is turned on and by charge quantity charged by the capacitor of large capacity in the case of long pulse width. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a signal reproducing apparatus including a bootstrap circuit unit that stably drives a high-side transistor in an amplification unit that amplifies a pulse signal.

  FIG. 2 shows a circuit diagram of a conventional signal reproducing apparatus.

  A conventional signal reproducing apparatus receives a totem pole type amplifying unit 30 that drives a load 50, and a control signal such as a PDM (Pulse Density Modulation) signal and a PWM signal (Pulse Width Modulation) that drives the totem pole type amplifying unit 30. A drive circuit section 10 that generates and a bootstrap circuit section 20 that supplies a drive voltage that stably turns on the high-side transistor T1 of the totem pole type amplification section 30 are provided. The totem pole type amplification unit 30 includes a high side transistor T1 and a low side transistor T2 which are switching transistors. The drive circuit unit 10 includes a high side drive circuit 12 and a low side drive circuit 14 that generate drive signals for driving the high side transistor T1 and the low side transistor T2.

  Furthermore, the bootstrap circuit unit 20 includes a diode D1 and a capacitor C1.

  Next, the connection relation of each part of the signal reproduction apparatus is shown below.

  A PDM signal that is an input signal of the signal reproducing device is input to the high-side drive circuit 12 and the low-side drive circuit 14 of the drive circuit unit 10. The output signal of the high side drive circuit 12 is connected to the gate of the high side transistor T1 of the totem pole type amplification unit 30. Similarly, the output signal of the low side drive circuit 14 is connected to the gate of the low side transistor T2 of the totem pole type amplification unit 30. The power supply terminal for supplying power to the drive circuit unit 10 is connected to the drive circuit power supply, and the ground terminal is connected to the ground 40.

  The drain of the high side transistor T1 of the totem pole type amplification unit 30 is connected to the output stage power supply V2. The source is connected to the drain of the low-side transistor T2 at the node N1 (first connection point). A load 50 (RL) is connected to the node N1, and the other terminal on the opposite side of the load is connected to the ground 40.

  Furthermore, the anode of the diode D1 of the bootstrap circuit unit 20 is connected to the drive circuit power supply V0, and the cathode of the diode D1 is connected to the capacitor C0 at the node N2 (second connection point). Similarly, the control signal terminal of the drive circuit unit 10 is connected to a node N2 to which the diode D1 and the capacitor C0 are connected. The other end of the capacitor C0 on the opposite side is connected to a node N1 to which the source of the high side transistor T1 and the drain of the low side transistor T2 are connected.

  Next, the operation of the conventional signal reproducing apparatus will be described.

  As shown in FIG. 2, a totem pole type amplification unit (a circuit in which a high side transistor T1 and a low side transistor T2 perform switching operations alternately) 30 is a final stage amplification circuit that amplifies a PDM signal or a PWM signal.

  When MOS_Nch switching elements are used in the upper and lower stages in the totem pole type amplification unit 30, when the lower low-side transistor T2 is in the “ON” state by the low-side drive circuit 14, the low-side transistor T2 is connected between the drain and source. Becomes a short circuit state. Therefore, the bootstrap circuit unit 20 including the diode D1 and the capacitor C0 is a closed circuit from the driving power supply V0 to the ground 40, and the capacitor C0 is charged from the power supply V0 through the diode D1.

  Next, when the low-side transistor T2 is “OFF” and the high-side transistor T1 is “ON”, the charge charged in the capacitor C0 is present at the gate of the high-side transistor T1 via the node N2 of the drive circuit unit 10. To charge the input capacitor (not shown in FIG. 2).

  Thus, in the conventional technique, when the lower low-side transistor T2 is shifted from “ON” to “OFF” and the upper high-side transistor T1 is driven from “OFF” to “ON”, The charge charged in the capacitor C0 charges an input capacitor (not shown in FIG. 2) existing at the gate of the high-side transistor T1, and secures a driving voltage that ensures that the high-side transistor T1 is in the “ON” state. (See Patent Document 1).

  However, the gate voltage V1, which is the drive voltage for the high-side transistor T1, is determined by the amount of charge (Q) accumulated in the capacitor C0. For example, when the low-side transistor T2 is turned “ON” with a short pulse width, the capacitor C0 having a predetermined rising characteristic may have a short charge time and may not be able to store sufficient charge.

Therefore, in order to obtain a sufficient driving voltage for driving the high-site transistor T1 regardless of the pulse width for turning on the low-side transistor T2, the high-side transistor T1 is turned on with the minimum “ON” time for the low-side transistor T2 to be “ON”. A capacitor C0 having a rising characteristic capable of charging a charge amount (Q) that can be driven is employed.
JP 05-252006 A

  However, if a small-capacitance capacitor C0, that is, a capacitor C0 having a short rise characteristic, is set in accordance with a short-width pulse that is the minimum time for which the low-side transistor T2 is “ON”, the high-side transistor T1 is turned on long. Since a capacitor C0 has a small capacity when a pulse having a width is input, the charged amount of charge (Q) secures a potential for stable driving during the period when there is a discharge of charge. There was a fear that it would be impossible. Conversely, when a large-capacitance capacitor C0, that is, a capacitor C0 having a relatively slow rising characteristic is set in accordance with a long-width pulse that drives the low-side transistor T2, a short-width pulse that turns on the low-side transistor T2 is input. In this case, the rising edge is delayed, and as a result, the charge amount (Q) to be charged becomes small, and there is a fear that the high-site transistor T1 cannot be driven. That is, it is difficult to reliably drive the high-side transistor T1 to “ON” with one capacitor C0 depending on whether the pulse width for turning on the low-side transistor T2 is long or short.

  Therefore, the present invention has been proposed in view of the above-described circumstances, and an object of the present invention is to reliably turn on the high side transistor regardless of the length of the pulse width for turning on the low side transistor. An object of the present invention is to provide a signal reproducing apparatus including a bootstrap circuit unit that can be used.

In the signal reproducing device according to the present invention, the source of the high-side transistor and the drain of the low-side transistor are connected via the first connection point, an output stage power supply voltage is applied to the drain of the high-side transistor, An amplifying unit that grounds a source and amplifies and outputs from the first connection point; a boost strap unit that has one end connected to a drive power supply and the other end connected to the first connection point;
The boost strap unit includes a diode and a plurality of capacitor groups connected in parallel. One end of the capacitor group is connected to the first connection point. The diode has an anode side for the drive power supply and a cathode side for the capacitor group. It is connected to the other end.
Further, the source of the high side transistor and the drain of the low side transistor are connected via a first connection point, an output stage power supply voltage is applied to the drain of the high side transistor, the source of the low side transistor is grounded, A totem pole type amplifier that amplifies and outputs from a first connection point, and one end of a plurality of capacitors are connected in parallel to the cathode side of the diode via a second connection point, and a drive power supply voltage is connected to the anode side of the diode And a high-side driving circuit connected to the second connection point in response to an input pulse is connected to the high-side transistor in response to an input pulse. The drive signal is input to the gate of the low-side transistor, and the low-side drive circuit drives the gate of the low-side transistor in the opposite phase to the drive signal. And a driving unit for inputting items,
When the high-side transistor is turned off and the low-side transistor is turned on with a minimum pulse width of the driving signal, the capacitor is charged, and when the high-side transistor is turned on and the low-side transistor is turned off, the capacitor is When discharging, the capacitance of the capacitor having the smallest capacitance among the capacitors is set so that the high-side transistor can be driven for a predetermined time.

  In this way, the bootstrap circuit unit is configured to connect a plurality of capacitors having rising characteristics and connect them in parallel, so that the high-side transistor can be driven stably regardless of the length of the drive pulse that turns on the low-side transistor. It is possible to ensure a driving voltage to be used. In particular, for a short drive pulse that turns on the low-side transistor, a stable drive voltage can be secured with the amount of charge charged by a capacitor having a small capacity and good rising characteristics.

  Since the signal reproduction apparatus according to the present invention has the above-described configuration, the following effects can be obtained.

  That is, it is possible to generate a drive voltage that stably drives the high-side transistor T1 regardless of the length of the drive pulse of the low-side transistor T2.

  Furthermore, by adopting a configuration in which a plurality of capacitors having different rising characteristics are connected in parallel, a more stable driving voltage is generated by assigning capacitors having different rising edges in accordance with the pulse width for turning on the low-side transistor T2. It is also possible.

  An embodiment of a signal reproduction apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of a signal reproducing apparatus including a bootstrap circuit unit according to the present invention.

  The signal reproducing apparatus according to the present invention is different from the conventional signal reproducing apparatus shown in FIG. 2 only in the bootstrap circuit unit 21. The bootstrap circuit unit 21 in FIG. 1 is a diagram illustrating an example configured with a diode D1 and two capacitors C1 and C2, and the capacitors C1 and C2 are connected in parallel.

  The high-side transistor T1 and the low-side transistor T2 of the totem pole type amplifying unit 30 may be a MOS FET element or a bipolar transistor element.

  First, the necessity of the bootstrap circuit unit 21 will be described below.

  In the circuit shown in FIG. 1, when the high-side transistor T1 in the totem pole type amplification unit 30 is sufficiently “ON”, the drain-source voltage of the high-side transistor T1 becomes almost 0 V, so that the source voltage is almost drained. The output stage power supply V2 is a voltage. Therefore, the gate voltage for sufficiently turning on the high-side transistor T1 needs to be a drive voltage equal to or higher than V2 + Vgs (Vgs: gate-source ON voltage; V2: output stage power supply voltage). If Vgs is + 10V, drive voltage V1 = V2 + 10V is required. That is, a drive voltage V1 higher than the output stage power supply voltage V2 is required.

  Until the high-side transistor T1 is sufficiently “ON”, the voltage at the node N1 rises toward V2. Then, in order to make the drive voltage reach V1 in a short time, a kind of feedback system is formed to generate the drive voltage.

  As described above, the bootstrap circuit unit 21 is provided in order to generate the drive voltage V1 higher than the output stage power supply voltage V2 in a short time under the low drive voltage generated only by the high-side drive circuit 12.

  Next, the operation of the bootstrap circuit unit 21 will be described in detail.

  As described above, when the low-side transistor T2 is “ON”, the low-side transistor T2 is short-circuited to the GND 40. Therefore, the capacitors C1 and C2 are charged from the power supply V0 for the drive circuit unit 10 via the diode D1 of the bootstrap circuit unit 21. Next, when the low-side transistor T2 is turned “OFF” and the high-side transistor T1 is driven to be “ON”, the charges charged in the capacitors C1 and C2 are transferred to the high-side via the drive circuit unit 10. Charging of a capacitor (not shown) existing at the gate of the transistor T1 is started. At this time, the potential at the node N2 becomes higher than the power supply voltage V0 of the drive circuit unit 10 as the source voltage of the high-side transistor T1 rises, so that the diode D1 is reverse-biased and is in a high-impedance state. Become. That is, the diode D1 is in the “OFF” state. Thereby, the diode D1 side and the capacitors C1 and C2 side are separated in terms of impedance. The charges charged in the capacitors C1 and C2 charge the input capacitor present at the gate of the high side transistor T1 through the high side drive circuit.

  As described above, when the low-side transistor T2 is “OFF”, the charges charged in the capacitors C1 and C2 can charge the input capacitor present at the gate of the high-side transistor T1 as described above, and the high-side transistor T1. It is possible to secure a drive voltage for turning on the power.

  Next, the operation of the bootstrap circuit unit 21 corresponding to the length of the input pulse (driving pulse of the low-side transistor T2) will be described.

  In general, as a capacitor performance, a capacitor having good rising characteristics (good frequency characteristics) is a small-capacitance capacitor, and a large-capacity capacitor has poor rising characteristics as compared with a small-capacitance capacitor. Therefore, from this point of view, the capacitor C1 is a capacitor having a fast rising characteristic that can accumulate charges that can sufficiently drive the high-site transistor T1 with respect to an input pulse having a short width. On the other hand, the capacitor C2 is a capacitor having a large capacity capable of accumulating sufficient charges for a long-width input pulse. Therefore, the capacitor 2 is necessarily slower than the rising characteristic of the capacitor C1.

  In this state, when the low-side transistor T2 is turned “ON” with a short pulse, charges are simultaneously accumulated in the capacitors C1 and C2. Therefore, the drive voltage V1 of the high-side transistor T1 is determined by the amount of charge stored in the capacitors C1 and C2 {charge amount QT≈ (C1 + C2) * V1; Q1≈C1 * V1; Q2≈C2 * V1}.

  The operation of the bootstrap circuit unit 21 when the pulse for driving the low-side transistor T2 is short under the conditions described above will be described.

  As described above, when the pulse is short, the capacitor C1 has a small capacity but is charged with the on-time of the low-side transistor T2 by the capacitor C1 having good rising characteristics, and charges (Q1) are accumulated.

  When the low-side transistor T2 is “OFF” and the high-side transistor T1 is “ON”, the amount of charge (Q1) stored in the capacitor C1 charges the input capacitor present at the gate of the high-side transistor T1. As described above, the gate voltage of the high-side transistor T1 is a capacitor having a small capacity and good characteristics, so that a sufficient charge can be stored even if the charging time is short. Since the pulse response characteristics are also good, the drive voltage of the high-side transistor T1 can be secured.

  On the other hand, the operation of the bootstrap circuit unit 21 when the pulse for driving the low-side transistor T2 is long will be described.

  When the drive pulse is long, the charge charged by the capacitor C1 is rapidly discharged after the minimum on-time of the high-side transistor T1 has elapsed. Therefore, the drive voltage cannot be held only by the capacitor C1. . Instead, the potential of the input capacitor of the high-side transistor T1 rises due to the amount of charge (Q2) of the capacitor C2, and the role of the capacitor C1 is switched to ensure the driving voltage of the high-side transistor T1, and during the pulse generation period It can be sustained.

  It is set so that the minimum pulse width time of the high side transistor T1 can be driven mainly by the amount of charge (Q1) charged in the capacitor C1 with the minimum on time of the low side transistor T2, and the capacitor C2 with a longer pulse width than that. If the charge (Q2) charged to 1 is set so that the high side transistor T1 can be driven, the shortage of the drive voltage can be solved regardless of the length of the ON pulse of the low side transistor T2.

  As described above, by connecting the capacitors C1 and C2 in parallel, a sufficient drive voltage for the high-side transistor T1 can be ensured regardless of the pulse length.

The above-described bootstrap circuit unit 21 has been described with respect to a circuit composed of two capacitors C1 and C2. However, the bootstrap circuit unit 21 has various rising characteristics depending on the time when the low-side transistor T2 is turned on. A plurality of capacitors may be allocated. In this way, it is possible to remove the restriction on the time during which the low-side transistor T2 is turned on, and it is possible to generate a more stable driving voltage.
In this embodiment, the input pulse is a PDM signal, but it may be a PWM signal or the like.

  The signal reproducing apparatus of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  The present invention can also be applied to an audio signal amplifying apparatus that efficiently amplifies an audio pulse signal such as a PDM signal or a PWM signal by a totem pole type amplification unit including a high side transistor and a low side transistor.

1 is a circuit diagram of a signal reproduction device according to the present invention. It is a circuit diagram of the conventional signal reproducing | regenerating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Drive circuit 12 High side drive circuit 14 Low side drive circuit 20 Bootstrap circuit part 21 Bootstrap circuit part 30 Totem pole type amplification part 40 GND
50 load

Claims (2)

The source of the high-side transistor and the drain of the low-side transistor are connected via a first connection point, an output stage power supply voltage is applied to the drain of the high-side transistor, the source of the low-side transistor is grounded, and the first An amplification section that amplifies and outputs from the connection point of
A boost strap unit having one end connected to the drive power source and the other end connected to the first connection point;
With
The boost strap unit includes a diode and a plurality of capacitor groups connected in parallel. One end of the capacitor group is connected to the first connection point. The diode has an anode side for the drive power supply and a cathode side for the capacitor group. A signal reproducing device connected to the other end. The source of the high-side transistor and the drain of the low-side transistor are connected via a first connection point, an output stage power supply voltage is applied to the drain of the high-side transistor, the source of the low-side transistor is grounded, and the first A totem pole type amplification section that amplifies and outputs from the connection point of
One end of a plurality of capacitors is connected in parallel to the cathode side of the diode via a second connection point, a drive power supply voltage is applied to the anode side of the diode, and the other end of the capacitor is connected to the first connection A bootstrap part connected to the point;
In response to the input pulse, the high-side driving circuit connected to the second connection point inputs a driving signal to the gate of the high-side transistor, and the low-side driving circuit has a phase opposite to that of the driving signal at the gate of the low-side transistor. A drive unit for inputting a drive signal of
With
When the high-side transistor is turned off and the low-side transistor is turned on with a minimum pulse width of the driving signal, the capacitor is charged, and when the high-side transistor is turned on and the low-side transistor is turned off, the capacitor is A signal regeneration device characterized in that, when discharging, a capacitor having a minimum capacitance among the capacitors is set so that the high-side transistor can be driven for a predetermined time.

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