JPS61113307A - Bootstrap circuit - Google Patents

Abstract

PURPOSE:To improve the power supply voltage utilizing efficiency and to prevent waveform distortion at a low frequency region by connecting a semiconductor element of diode operation and a resistive element in parallel between a bootstrap terminal and a power terminal. CONSTITUTION:A diode 4 and a resistor 9 are connected in parallel between the bootstrap terminal 3 of an amplifier 1 and the power terminal 8. The resistance of the resistor 9 is selected so that the voltage across the resistor 9 is smaller than the forward voltage of the diode 4. Thus, the voltage at the terminal 3 depends on the voltage drop across the resistor 9 because the diode 4 is turned off. Since the voltage drop by the resistor 9 is small without signal input, the amplifier 1 is operated at a low power supply voltage. Further, when a signal is inputted, the diode 4 is conductive and a bootstrap capacitor 5 is charged rapidly. Thus, no missing is caused in the output waveform. Thus, the power voltage utilizing efficiency is improved and waveform distortion at a low frequency region is avoided.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to improvements in bootstrap circuits.

(Configuration of conventional example and its problems) Figure 1 shows a conventional example of a bootstrap circuit, where 1 is an amplifier, 2 is an input terminal, 3 is a bootstrap terminal, 4 is a diode, and 5 is a bootstrap circuit. A capacitor, 6 is an output terminal, 7 is a load, and 8 is a power supply terminal.

In the conventional example configured in this way, the input terminal 2 of the amplifier 1
In a static state where no input signal is applied, the potential of the bootstrap terminal 3 is lower than the power supply voltage by the voltage drop caused by the diode 4. For this reason, there has been a problem in that the power supply voltage at which the amplifier 1 can operate is lowered.

FIG. 2 shows a second conventional example of the bootstrap circuit, and the difference from FIG. 1 is that the diode 4 is replaced with a resistor 9. In the circuit configuration shown in FIG. 2, the potential of the bootstrap terminal 3 when no signal is input is determined by the current flowing through the resistor 9. Therefore, by reducing the resistance value of resistor 9, the voltage drop will be reduced, and the first
The power supply voltage is used more efficiently than the one shown in the figure. However, on the other hand, the discharging time of the bootstrap capacitor 5 is shortened, resulting in the disadvantage that the upper part of the output waveform is missing in the low frequency region.

(Object of the Invention) The present invention has been made to eliminate all the disadvantages seen in the above-mentioned conventional examples, namely, to improve the power supply voltage usage efficiency of the bootstrap circuit and to reduce waveform distortion in the low frequency region. This provides a bootstrap circuit that does not cause

(Structure of the Invention) To summarize, the present invention includes a bootstrap circuit in which a semiconductor element that operates as a diode and a resistance element are connected in parallel between a bootstrap terminal and a power supply terminal.
According to this, operation at a low power supply voltage is possible, and waveform distortion can be eliminated.

(Description of Embodiment) FIG. 3 shows an embodiment of the bootstrap circuit according to the present invention. Components that are the same as those in FIGS. 1 and 2 are designated by the same reference numerals. The features of the present invention are:
A diode 4 and a resistor 9 are connected in parallel between the bootstrap terminal 3 of the amplifier 1 and the power supply.

The bootstrap circuit according to the present invention is configured as described above, and when the amplifier is in a resting state, the current flowing into the amplifier from the bootstrap terminal 3 is I, (A), and the value of the resistor 9 is R2. In the case of (c), the relationship I, XR2<0.7V can be satisfied by setting the value of R2. At this time 1. The potential of the Gutstra y7° terminal 3 is a value lower than the power supply voltage by ×R2 (V), and if this value is set to be smaller than the forward voltage of the diode, the diode 4 will be in the off state. be placed. Therefore, the potential of the bootstrap terminal in the quiescent state of the bootstrap circuit according to the present invention is higher than that of the conventional example shown in FIG. It will be low.

Next, when an input voltage is applied to the input terminal 2 of the amplifier 1 and the output terminal 6 changes to a lower value than the quiescent state, the first
In both the conventional example shown in the figure and this embodiment, the diode 4 is turned on and the bootstrap capacitor 5 is rapidly charged. The amount of charge can be charged in a much shorter time than charging through the resistor 9 as in the conventional example shown in FIG.

Next, when an input voltage is applied to the input terminal 2 of the amplifier 1 and the output terminal 6 changes to a higher value than the quiescent state, the charge stored in the bootstrap capacitor 5 passes through the resistor 9 to the power supply terminal 8. discharged to.

In this way, when an AC signal is input to the amplifier, when the signal frequency is low, that is, when a signal with a long period is applied, in the conventional example shown in FIG. 2, the bootstrap capacitor 5 is discharged before it is sufficiently charged. However, in the circuit configuration according to the present invention as shown in FIG. 3, the bootstrap capacitor 5 can be charged rapidly, so that the upper part of the output waveform is not missing.

Figures 4, 5, and 6 represent Figures 1, 2, and 6, respectively.
The waveforms of the output terminal 6 and the bootstrap terminal 30 are shown when an amplifier having a circuit configuration corresponding to that shown in FIG. The input signal to each amplifier 1 is a rectangular wave with a frequency of 100 Hz, and the input signal is input from 5 m5ec on the horizontal axis (time axis) shown in the figure. The magnitude of the input signal is set to be large enough to saturate the output of the amplifier 1, and the saturation voltage of the amplifier 1 is set to 0.5V.

When the potential of the output terminal 6 in a resting state (masu→yoυ) becomes high, the amplifier 1 consumes a current of, for example, 25 mA (hereinafter, this current 1 cycle is written as ■2) from the bootstrap terminal 3, At other times, it is assumed that, for example, a current of 1 mA is supplied from the bootstrap terminal 3. Also, the resistor 9 is 100Ω, and the bootstrap capacitor 5 is 100μF.

First, let us consider a static state in which no input signal is input to the amplifier 1. In the circuit shown in FIG. 1, the potential of the bootstrap terminal 3 is about 0.7 V lower than the power supply voltage.

In order for amplifier 1 to operate, bootstrap terminal 3
The potential difference between the output terminal 6 and the output terminal 6 must be at least a certain value (hereinafter, this potential difference will be referred to as Va). Therefore, the minimum operating power supply voltage (hereinafter this voltage will be written as vcc (M)) is the potential difference between the power supply voltage and bootstrap terminal 3 (hereinafter this potential difference will be written as "b") plus va. is the power supply voltage when the difference between the output terminal voltage in the static state and the power supply voltage is equal.The output voltage in the static state is v
cc(gxs) = 2 x (Va +Vb) tonal.

For example, if va=1v, then in the circuit shown in FIG. 1, the lowest operating power supply voltage is vb=0.7v, so vc
o(MIN)=2×(0,7+1)=3.4v,
In the circuit shown in FIGS. 2 and 3, vb=R2×11=1
00Ω×1 mA = 0. I V, so v
'=2x(0,1+1)=2.2vcc(yl
N), and the minimum operating power supply voltage differs by 1.2V.

Next, a case where a 100 Hz input signal is input to the amplifier 1 will be explained. When a positive signal is input to the input terminal 2 of the amplifier 1 and the potential of the output terminal 6 increases, the bootstrap capacitor 5 connects the bootstrap capacitor 5 to the bootstrap capacitor 5. It rises while maintaining the potential difference,
After that, in the circuit shown in FIG. 1, the charge is discharged from the bootstrap capacitor 5 by the current I2, and the potential of the bootstrap terminal 3 (hereinafter, this potential is written as vBs) decreases with time. The circuit capacitor 5 shown in FIGS. 2 and 3 is discharged, and the potential of the bootstrap terminal 3 decreases.

At this time, the voltage at the output terminal 6 of the amplifier 1 requires a certain potential difference between the bootstrap terminal 3 and the bootstrap terminal 3 (hereinafter, this potential difference is referred to as vc), so the potential at the bootstrap terminal 3 is V. When the voltage at the output terminal 6 decreases to ut+"c, the voltage at the output terminal 6 thereafter decreases while maintaining the potential difference between the voltage at the bootstrap terminal 3 and the power supply voltage v0, causing a chip in the output waveform.

Next, when a negative signal is input to the input terminal 2 of the amplifier 1 and the potential of the output terminal 6 decreases, the bootstrap terminal 3
decreases while maintaining the potential difference across the bootstrap capacitor 5, and thereafter, in the circuits shown in Figures 1 and 3, the bootstrap capacitor 5 is
1il- The strap capacitor 5 is rapidly charged, and the bootstrap capacitor 5 is almost instantaneously charged.

-0.7V.

The bootstrap capacitor 5 is charged, and the potential of the bootstrap terminal 3 increases with time.

The waveforms of the bootstrap terminal 3 and the output loop 6 exhibit the behavior described above, and in the conventional circuit example shown in FIG. Compared to the second example, the potential of the bootstrap terminal 3 in a stationary state is lower, and therefore the minimum operating power supply voltage is higher. The conventional circuit example shown in FIG. 2 has a low minimum operating power supply voltage, but has the disadvantage of causing a chip in the output waveform.

The circuit shown in FIG. 3 according to the present invention is advantageous in that the output waveform does not have any gaps after the first wave, and the minimum dynamic surface power supply voltage is low.

FIG. 7 shows a specific circuit example of the present invention. resistor ll
The connection point between 2 and the capacitor 43 is a ripple filter that is not susceptible to fluctuations from the power supply, and based on this connection point, the power supply is connected to the collector, and the bootstrap terminal is connected to the emitter. The transistor nostar 41 with diode action and the resistor 9 between the power supply terminal 8 and the bootstrap terminal 3 represent the characteristic parts of this circuit.

Output/Gubu NPN that constitutes the Bushuguru output circuit
The l-lannostars 56,57 are driven by NPN l-lannostars 50 and PNP transistors 55, respectively, which are connected to diode 16.47°53.
54 and NPN) are coupled by a bias circuit formed by a lannostar 52. The input to this amplifier is amplified in the previous stage and input to the signal source 49 as a current signal.

Constant current source 48 and PNP transistors 44 and 45
.

Each of the circuits 51 and 51 supplies a constant current to the drive stage of the amplifier circuit.

The output terminal 6-2 of this amplifier circuit is connected to a load 7 via a capacitor 5, and is also connected to a bootstrap terminal 3 via a bootstrap capacitor 5.

In this circuit, if the current value of constant current #48 is 1 mA, the above 11 = 3 mA, and Va is the saturation voltage of PNP of 0.
If it is 2v, it is about 1.6v.

Therefore, the minimum operating power supply voltage is 2X (1 mAxtoon + 1.6 V) = 3.8 V, assuming that resistor 9 is 1000.
becomes.

(Effects of the Invention) According to the present invention, it is possible to easily realize a bootstrap circuit that has high power supply voltage utilization efficiency and does not cause output waveform distortion in a low frequency region.

[Brief explanation of drawings]

1 and 2 are conventional bootstrap circuit diagrams, FIG. 3 is a bootstrap circuit diagram of an embodiment of the present invention, and FIGS. 4, 5, and 6 are respectively conventional bootstrap circuit diagrams.
7 are specific circuit diagrams of the bootstrap circuit of the present invention. 1...Amplifier, 2-...Input terminal, 3...Bootstrap terminal, 4...Diode, 5...Bootstrap capacitor, 6...Output terminal, 7...Load,
8...Power terminal, 9...Resistor. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] A bootstrap circuit characterized in that a semiconductor element that operates as a diode and a resistance element are connected in parallel between a bootstrap terminal and a power supply terminal.