JP2614938B2 - Charge pump device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge pump device, and more particularly to a charge pump device incorporated in a semiconductor integrated circuit (hereinafter abbreviated as IC) by optimizing current consumption.

[Conventional technology]

The conventional charge pump circuit, as shown in FIG.
A ring oscillator 50 for connecting an odd number of inverters, returning the last stage to the first stage and self-oscillating, a charge pump circuit 51 for switching the capacitor charging circuit using the output of the ring oscillator 50 as a switching signal, and a charge pump circuit And a clamp circuit 52 for clamping an excessive boosted voltage of the output. The charge pump circuit shown in FIG. 5 utilizes the inherent delay time of the inverter,
An odd number of inverters are connected to form a positive feedback loop to form an oscillation circuit. _Assuming that the sum of the rise delay time and the _fall delay time of each inverter is t _diNV , and the number of connected inverters is n, the oscillation frequency of the ring oscillator 50 is approximately f _式 1 / (T _dINV × n) (1) It is calculated. There are various examples of the internal circuit of the charge pump circuit. For example, FIG. 3 shows an example of a charge pump circuit having a triple booster circuit 30 for generating a triple voltage. In the clamp circuit of this example, in order to obtain a desired output voltage, the voltage is increased in advance to a higher voltage,
The extra voltage is controlled by the clamp circuit.

Another conventional example is shown in FIG. In this example, the constant voltage circuit 60
And a charge pump circuit that obtains an output voltage of m × V _ref by boosting the voltage by m times using the output V _{ref of the} constant voltage circuit as a reference voltage
61 and has. This example is widely used as a power supply for driving a liquid crystal of a watch IC or a calculator IC.

[Problems to be solved by the invention]

In the prior art shown in FIG. 5, the oscillation frequency of the ring oscillator is fixed at the stage when the constituent circuit is determined, and the current consumption of the ring oscillator is large irrespective of the load of the output of the charge pump circuit. Was an obstacle. In addition, there is a clamp circuit in the output section, and the desired output voltage is determined by the setting accuracy of the clamp voltage.
There is a drawback that increasing the precision with the built-in increases the cost.

In the conventional example shown in FIG. 6, since the output voltage can be obtained as m × _Vref , the output voltage can be obtained with high accuracy. However, when the load increases, the voltage drop is interpolated. Therefore, the application has been limited to a drive circuit of a liquid crystal display.

An object of the present invention is to provide a charge pump device that obtains a desired output voltage with a minimum required current consumption.

[Means for solving the problem]

In order to achieve the above object, a charge pump device according to the present invention is a charge pump device having a charge pump circuit, a voltage divider circuit, an error amplifier, and a VCO, wherein the charge pump circuit includes a capacitor connected by switching. It charges and raises or lowers the DC voltage. The voltage divider divides the output of the charge pump circuit.The error amplifier compares the output of the voltage divider with the reference voltage to determine the error. The VCO amplifies the voltage and outputs a voltage control signal for the VCO. The VCO includes a plurality of stages of inverters connected in series and load transistors provided in the inverters of each stage. Input the voltage control signal from the amplifier to vary the on-resistance of the load transistor,
Feedback is performed during the entire clock period to change the oscillation frequency.

[Action]

A feedback unit is provided for modulating the switching frequency of the input of the charge pump circuit according to the degree of load of the charge pump circuit. The VCO (Voltage Controlled) switches the switching frequency of the charge pump circuit, which is the voltage divider circuit and error amplifier, to the optimum frequency depending on the load level.
Oscillator) is added to the function of the ring oscillator.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

 FIG. 1 is a configuration diagram showing one embodiment of the present invention.

In the figure, in the present embodiment, a charge pump circuit 1 for charging a capacitor by switching, a voltage dividing circuit 2 for dividing the output of the charge pump circuit 1, a comparison between the output of the voltage dividing circuit 2 and a reference voltage are performed. An error amplifier 3 that amplifies a voltage, and a VCO (Vol.) That outputs a switching signal of the charge pump circuit 1 by using an output of the error amplifier 3 as a control voltage.
Stage Controlled Oscilltor) 4. Also, 5
Indicates a load.

For more specificity, the embodiment of FIG. 2 will be described. FIG. 2 is an example specifically showing an internal circuit having the configuration of FIG. As an example of the charge pump circuit 1, a double voltage booster circuit that has been used in the past is used. That is, in this embodiment, an output voltage V ₀ = 2 × V _cc is obtained. here,
The double voltage boosting circuit has MOS transistors T _{1 to} T ₈ and capacitors C ₁ and C ₂ , and the operation thereof is already a well-known technology and will not be described.
The triple voltage booster circuit 30 shown in the figure or the 1/2 voltage booster circuit 40 in FIG. 4 can be replaced as it is.

The voltage dividing circuit 2 has resistors r ₁ and t ₂ and a capacitor C ₃ , and divides the output V ₀ of the charge pump circuit 1 into r ₂ / (r ₁ + r ₂ ). That is, the output V _i of the voltage dividing circuit 2 can be calculated as follows: V _i = {r ₂ / (r ₁ + r ₂ )} · V ₀ (2) The error amplifier 3 is connected to a reference voltage V _ref to the non-inverting input, the output V _i of the voltage dividing circuit 2 through a resistor r _3, constituting a differential amplifier connected to the inverting input. When applying a negative feedback between the inverting input and the differential amplifier output resistance r _4,
The output V _c of the error amplifier 3 can be expressed by equation (3).

_{V c = V ref - (r} 4 / r 3) (V i -V ref) ... (3) that is, V _c to a voltage control input of the VCO 4, the reference voltage V _ref
Of the voltage divider circuit 2 mainly output V _i and the reference voltage V _ref difference (V _i
−V _ref ) is amplified by r ₄ / r ₃ times to obtain a voltage whose polarity is inverted. The circuit configuration of VCO 4 has MOS transistors T _{9 to} T ₂₂ , deforms the ring oscillator circuit, and voltage-controls the gate voltages of load transistors T ₁₀ , T ₁₂ , T ₁₄ , T ₁₆ and T ₁₆ of the inverter, connected to the output V _c of the error amplifier 3.

When Thus, when the output V _c of the error amplifier 3 is increased, the load current characteristic of the inverter of the ring oscillator increases, the oscillation frequency becomes higher. When the oscillation frequency increases, the switching speed of the charge pump circuit 1 also increases, and the output V ₀ of the charge pump circuit 1 also increases. As a result, feedback that the output V _i of the voltage dividing circuit 2 increases and the output V _c of the error amplifier 3 decreases according to the equation (3) is applied, and automatic control operates.

Summarizing equations (2) and (3), the output of the error amplifier
Between the V _c and a charge pump circuit output _{V 0, V C = V ref} - (r 4 / r 3) {[r 2 / (r 1 + r 2)] · V 0 -V ref} ... (4 ) Holds.

The load current I _L of the individual inverters of the ring _{oscillator, I L = 1 / 2β (} V C -V T) 2 ... (5) (β is-conduction coefficient of the MOS transistor) can be expressed as, 5 in this embodiment of connecting the number of inverters including waveform amplifying inverter, can be calculated the current consumption of the ring oscillator as 6 × I _L, it operates with minimum current consumption to obtain an output V ₀ as a charge pump circuit configured It has become.

〔The invention's effect〕

As described above, the present invention provides a
With the O configuration, a charge pump circuit can be realized with the minimum current consumption required to obtain a desired output voltage V ₀ , which is an extremely effective means of incorporating an IC.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a detailed internal circuit diagram of the configuration shown in FIG.
FIG. 4 is a diagram showing a triple voltage boosting circuit of the charge pump circuit shown in FIG. 4;
FIG. 5 is a view showing a conventional charge pump circuit, and FIG. 6 is a view showing a conventional circuit for charge pumping a reference voltage. 1 charge pump circuit 2 voltage divider circuit 3 error amplifier 4 VCO 5 load T _{1 to} T ₂₂ MOS transistors C _{1 to} C ₃ capacitors r _{1 to} r ₄ …resistance

Claims (1)

(57) [Claims] 1. A charge pump device comprising a charge pump circuit, a voltage dividing circuit, an error amplifier, and a VCO, wherein the charge pump circuit charges a capacitor by switching and boosts or drops a DC voltage. The voltage divider divides the output of the charge pump circuit. The error amplifier compares the output of the voltage divider with the reference voltage,
The VCO amplifies the error voltage and outputs a voltage control signal to the VCO. The VCO includes a plurality of inverters connected in series and load transistors provided in the inverters of each stage. A charge pump device which receives a voltage control signal from an error amplifier, varies the on-resistance of a load transistor, and performs feedback during the entire clock period to change the oscillation frequency.