Reference voltage generator

Abstract

The invention provides a reference voltage generator, which comprises a multi-voltage generating circuit, a reference voltage generating circuit, a reference voltage generating circuit and a reference voltage generating circuit, wherein the multi-voltage generating circuit is used for generating a plurality of voltages with different levels; the plurality of voltage selection and time-sharing output circuits are used for selecting at least two different voltages from the plurality of voltages with different levels generated by the multi-voltage generation circuit according to the high and low levels of a PWM (Pulse-Width Modulation) signal, and outputting the selected voltages in a time-sharing manner; and the low-pass filtering circuit is used for carrying out low-pass filtering on the voltage output by the plurality of voltage selection and time-sharing output circuits to generate reference voltage.

Description

Technical Field

[0001] The present invention relates to a reference voltage generator, which can generate multiple levels of reference voltages for selection by modulating the duty ratio of a pulse width modulation (PWM) signal. Background Art

[0002] Since the reference voltage level generated by the reference voltage generator may not necessarily meet the needs, a trimming function is required, that is, a plurality of reference voltage levels need to be provided so that the most suitable selection can be made in actual use. Figure 1 , showing a reference voltage generator 10 of the prior art. Among them, the voltage generated by the current i flowing through the resistor R1 generates a corresponding voltage on the resistor RX in proportion to the relationship between the resistor RX and the resistor R1. The resistor RX includes a plurality of resistors connected in series, so different voltages V1 to Vn can be obtained at different nodes between the resistors. The multiplexer circuit MUX outputs one of the voltages V1 to Vn as the reference voltage VBG according to the selection signal. The selection signal is an m-bit digital signal, and the number of bits determines the precision of the reference voltage VBG that can be generated (that is, how many levels of reference voltage VBG can be provided for selection); 2 m =n.

[0003] The disadvantage of the above-mentioned prior art is that if more levels of reference voltage VBG are to be provided as options, that is, the higher the number of m is, the number of resistors required to be provided in the resistor RX will also increase accordingly, resulting in an increase in the circuit area.

[0004] The present invention proposes a solution to the above problem, which can significantly increase the precision of the reference voltage VBG in a smaller circuit area. Summary of the invention

[0005] From one viewpoint, the present invention provides a reference voltage generator comprising: a multiple voltage generating circuit for generating multiple voltages of different levels; a multiple voltage selection and time-sharing output circuit for selecting at least two different voltages from the multiple voltages of different levels generated by the multiple voltage generating circuit according to the high and low levels of a PWM signal, and outputting them in a time-sharing manner; and a low-pass filtering circuit for generating a reference voltage after low-pass filtering the voltages output by the multiple voltage selection and time-sharing output circuits.

[0006] In one preferred implementation, the level of the reference voltage is related to the duty cycle of the PWM signal.

[0007] In one preferred embodiment, the multiple voltage selection and time-sharing output circuit includes: a multiplexing circuit that selects at least two different voltages from multiple voltages of different levels generated by the multiple voltage generating circuit according to a selection signal; and a switching selection circuit that outputs the at least two different voltages in a time-sharing manner according to the high and low levels of the PWM signal.

[0008] In one preferred embodiment, the multiple voltage selection and time-sharing output circuit includes: a selection signal control circuit, which receives a first selection signal and the PWM signal and generates a second selection signal, wherein the first selection signal is used to select at least two different voltages from a plurality of voltages of different levels generated by the multiple voltage generating circuit; the selection signal control circuit determines a voltage from the at least two different voltages according to the high and low levels of the PWM signal; the second selection signal corresponds to the determined voltage; and a multiplexing circuit, which selects the determined voltage output from the plurality of voltages of different levels generated by the multiple voltage generating circuit according to the second selection signal.

[0009] In one preferred implementation, the PWM signal is derived from a clock signal.

[0010] The following is a detailed description through specific embodiments to make it easier to understand the purpose, technical content, characteristics and effects achieved by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 FIG. 2 shows the structure of a reference voltage generator in the prior art.

[0012] Figure 2 An embodiment of the reference voltage generator of the present invention is shown.

[0013] Figure 3 Several embodiments of PWM signals used with the reference voltage generator of the present invention are shown.

[0014] Figure 4 , Figure 5 Two other embodiments of the reference voltage generator of the present invention are shown.

[0015] Explanation of symbols in the figure

[0016] 1, 2, 3 Waveform

[0017] 20, 30, 40 Reference voltage generator

[0018] 21 Multiple voltage generation circuit

[0019] 22, 22' Multiplex Circuit

[0020] 23 Switching selection circuit

[0021] 24 Low pass filter circuit (LPF)

[0022] 25 Select signal control circuit

[0023] 26 Multiple voltage selection and time-sharing output circuit

[0024] A, B selection signal

[0025] H High level

[0026] i Current

[0027] L Low level

[0028] R1, RX resistor

[0029] V1~Vn,V(x),V(x+1),V(y) voltage

[0030] VBG reference voltage DETAILED DESCRIPTION

[0031] The drawings in the present invention are schematic diagrams, and are mainly intended to show the relationship between various circuit components. The shapes and sizes are not drawn according to scale.

[0032] See also Figure 2 , showing a reference voltage generator 20 , which is one embodiment of the present invention. The reference voltage generator 20 includes a multi-voltage generating circuit 21 , a multiplexing circuit 22 , a switching selection circuit 23 , and a low-pass filter circuit (LPF) 24 .

[0033] The multiple voltage generating circuit 21 corresponds to Figure 1 The circuit on the left is omitted for simplicity. Figure 1 .

[0034] The multiplexer circuit 22 selects two voltages from the voltages V1 to Vn generated by the multiple voltage generating circuit 21 according to the selection signal. In this embodiment, two adjacent voltages V(x) and V(x+1) are selected, i.e., V1 and V2, or V2 and V3, etc. However, in other embodiments, the two adjacent voltages V(x) and V(x+1) are not necessarily required, but may be any two voltages.

[0035] The switching selection circuit 23 switches and selects between the two voltages output by the multiplexing circuit 22 according to the PWM signal. Figure 3In the present embodiment, when the PWM signal is at a low level L, the switching selection circuit 23 selects the voltage V(x); when the PWM signal is at a high level H, the switching selection circuit 23 selects the voltage V(x+1) (of course, the opposite arrangement is also feasible).

[0036] The output of the switch selection circuit 23 generates a reference voltage VBG after passing through a low-pass filter circuit (LPF) 24 .

[0037] Figure 3 Displays multiple examples of PWM signals. See Figure 3 And compare Figure 2 In the case of waveform 1, the duty ratio of the PWM signal is 50% (i.e., the ratio of the high level H to the low level L is 1:1), at which time, the reference voltage VBG is equal to (50%)*V(x+1)+(50%)*V(x); in the case of waveform 2, the duty ratio of the PWM signal is 67% (i.e., the ratio of the high level H to the low level L is 2:1), at which time, the reference voltage VBG is equal to (67%)*V(x+1)+(33%)*V(x); in the case of waveform 3, the duty ratio of the PWM signal is 33% (i.e., the ratio of the high level H to the low level L is 1:2), at which time, the reference voltage VBG is equal to (33%)*V(x+1)+(67%)*V(x). Obviously, if the duty ratio of the PWM signal is adjusted to other ratios, any level between the voltages V(x) and V(x+1) can be obtained as the reference voltage VBG.

[0038] See also Figure 4 , showing a reference voltage generator 30, which is another embodiment of the present invention. The reference voltage generator 30 includes a multiple voltage generating circuit 21, a multiplexing circuit 22', a low pass filter circuit (LPF) 24, and a selection signal control circuit 25. Among them, the functions of the multiple voltage generating circuit 21 and the low pass filter circuit (LPF) 24 are the same as those of the previous embodiment, so they are not repeated.

[0039] In this embodiment, the selection signal A is equivalent to the selection signal in the previous embodiment, and two voltages are selected from the voltages V1 to Vn generated by the multiple voltage generating circuit 21. The PWM signal is input to the selection signal control circuit 25. The selection signal control circuit 25 generates a selection signal B according to the level of the PWM signal, and selects one of the two voltages selected by the selection signal A, so that the multiplexing circuit 22' generates a voltage V(y). Although the circuit structure is slightly different from that of the previous embodiment, similarly, the voltage V(y) will change between two levels. After passing through the low-pass filter circuit (LPF) 24, a voltage between the two levels can be generated as a reference voltage VBG, and the level of the reference voltage VBG can be determined by the duty ratio of the PWM signal.

[0040] See also Figure 5 , showing the reference voltage generator 40, is another embodiment of the present invention. From a more macroscopic perspective, Figure 2 The multiplexing circuit 22 and the switching selection circuit 23 of the embodiment, or Figure 5 The multiplexing circuit 22' and the selection signal control circuit 25 of the embodiment can be regarded as a multiple voltage selection and time-sharing output circuit 26. The multiple voltage selection and time-sharing output circuit 26 selects at least two different voltages from the multiple voltages generated by the multiple voltage generating circuit 21 according to the high and low levels of the PWM signal, and outputs them in time-sharing. Therefore, the reference voltage VBG generated by the low-pass filter circuit (LPF) 24 will have a level between the two voltages, and the voltage level can be determined by the duty ratio of the PWM signal.

[0041] Worth noting: Figure 5 In the embodiment, the selection signal is not shown because when the number of voltages generated by the multi-voltage generating circuit 21 is two, the selection signal is not needed, and the present invention can still generate a reference voltage VBG with relatively high precision.

[0042] Compared with the prior art, which can only generate n fixed-level reference voltages VBG, the present invention can generate various levels of reference voltages VBG by modulating the duty ratio of the PWM signal without adding a resistor RX (see Figure 1 ) can greatly save circuit area, which is far better than the existing technology.

[0043] On the other hand, although in more precise applications, a higher precision reference voltage VBG can be obtained by modulating the duty ratio of the PWM signal, in the simplest application, the duty ratio of the PWM signal can be simply maintained at 50%; in this case, the PWM signal can be conveniently obtained from the existing clock signal in the circuit. Even if the duty ratio of the PWM signal is not modulated, the present invention can still provide higher precision than the prior art.

[0044] The present invention has been described above with respect to the preferred embodiment, but the above is only to make it easy for those skilled in the art to understand the content of the present invention, and is not intended to limit the maximum scope of the present invention. Under the same spirit of the present invention, those skilled in the art can think of various equivalent changes. For example, the voltage selected by the multiplexing circuit 22 does not have to be two voltages, but can be any number of voltages; the meanings of the high and low levels of the PWM signal can be interchanged; when the number of voltages generated by the multiple voltage generating circuit is two, the selection signal can be omitted; between the two circuits directly connected in the icon, other circuits that do not affect the main functions of the circuits, such as switches, buffers, etc., can be added. The scope of the present invention should cover the above and all other equivalent changes.

Claims

1. A reference voltage generator, comprising: A multi-voltage generating circuit for generating a plurality of voltages of different levels; a plurality of voltage selection and time-sharing output circuits, which select at least two different voltages from a plurality of voltages of different levels generated by the multiple voltage generating circuits according to the high and low levels of a PWM signal, and output them in a time-sharing manner; and A low-pass filter circuit generates a reference voltage after low-pass filtering the voltages output by the multiple voltage selection and time-sharing output circuits.

2. The reference voltage generator as claimed in claim 1, wherein: The level of the reference voltage is related to the duty cycle of the PWM signal.

3. The reference voltage generator as claimed in claim 1, wherein: The multiple voltage selection and time-sharing output circuit comprises: a multiplexing circuit that selects at least two different voltages from a plurality of voltages of different levels generated by the multiple voltage generating circuit according to a selection signal; and A switching selection circuit outputs the at least two different voltages in a time-sharing manner according to the high and low levels of the PWM signal.

4. The reference voltage generator as claimed in claim 1, wherein: The multiple voltage selection and time-sharing output circuit comprises: a selection signal control circuit receiving a first selection signal and the PWM signal and generating a second selection signal, wherein the first selection signal is used to select at least two different voltages from a plurality of voltages of different levels generated by the multi-voltage generating circuit; the selection signal control circuit determines one voltage from the at least two different voltages according to the high and low levels of the PWM signal; and the second selection signal corresponds to the determined voltage; and A multiplexing circuit selects the determined voltage output from a plurality of voltages of different levels generated by the multiple voltage generating circuit according to the second selection signal.

5. The reference voltage generator as claimed in claim 1, wherein: The PWM signal is derived from a clock signal.

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