JP3359407B2 - Signal generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal generation circuit for generating an operation reference signal in an analog circuit.

In an analog circuit for amplifying an audio signal or the like, it is necessary to appropriately set an operation reference signal so as not to cause distortion in the signal. Usually, the operation reference signal is fixedly set substantially at the center of the power supply voltage.
Therefore, when a power supply voltage such as a battery power supply is reduced, a signal is distorted. Alternatively, when a circuit designed with a power supply voltage of 5 volts is used with a power supply of 3 volts, the signal is similarly distorted, but the circuit operates normally using either a power supply of 5 volts or 3 volts. May be requested.

[0003] The present invention relates to a signal generation circuit that always outputs an appropriate operation reference signal regardless of the power supply voltage in such a case.

[0004]

2. Description of the Related Art FIG. 7 is an explanatory view of a conventional technique. FIG.
(a) shows a conventional operation reference signal generation circuit.

In FIG. 7A, reference numeral 100 denotes a power supply voltage, which represents the voltage of a power supply such as a battery. 101 is a reference signal generation circuit. An operation reference signal for signal processing of an analog circuit is generated.

Reference numeral 102 denotes a reference signal generator, which fixedly generates a signal of 1/2 of a normal power supply voltage. 103 is an analog circuit.

[0007]

FIG. 7B is an explanatory diagram of a problem caused by the conventional signal generation circuit. FIG.
In (b), VE is a power supply voltage.

VE 'indicates the level of the power supply voltage when the power supply voltage drops. VR is an operation reference signal. When the power supply voltage was 5 volts, the operation reference voltage VR was constant at 2.5 volts, which is １ ／ of the normal power supply voltage VE. Assuming that the threshold value of the active element of the analog circuit 103 is 1 volt, the amplitude of a signal that can be processed by the analog circuit 103 is in the range of 4-1V. As a result, the power supply voltage VE lowers to 4 V
Until, the analog circuit 103 can perform signal processing without causing distortion. However, when the power supply voltage becomes VE 'of 4 V or less, the amplitude of a signal that does not cause distortion becomes smaller than when the normal power supply voltage VE.

An object of the present invention is to provide a signal generating circuit which always outputs an appropriate operation reference signal regardless of a power supply voltage.

[0010]

FIG. 8 is an explanatory diagram of the means for solving the problem. FIG. 8 is an explanatory diagram of the operation of the analog circuit when the power supply of 5 volts is replaced with the power supply of 3 volts.

When the power supply voltage VE = 5 volts, the operation reference voltage is VR = 2.5V. At this time, the maximum value A _{0 of the} signal can take 1.5 V (see waveform a). Assuming that the power supply voltage becomes VE '= 3 V with the operation reference voltage VR kept at 2.5 V, the maximum amplitude at which a signal without distortion is obtained is 0.5 V (see waveform b). When the power supply voltage VE '= 3V, the operation reference voltage is lowered and VR'
= 2.0V, the amplitude that can be processed without distortion is 1
V (see waveform c).

Therefore, when the power supply voltage is lowered, if the operation reference signal is lowered in accordance with the lowered power supply voltage, it is possible to maintain an amplitude large enough to allow normal signal processing.

According to the present invention, a decrease in the power supply voltage is automatically detected, and a plurality of levels of operation reference signals can be automatically output in accordance with the power supply voltage. FIG. 1 shows a basic configuration of the present invention.

In FIG. 1, reference numeral 1 denotes a signal generation circuit.
2 is a power supply voltage.

2 'is an analog circuit. In the signal generation circuit 1, reference numeral 3 denotes an input signal conversion circuit for converting the power supply voltage 2 into an operation enable signal of the comparison circuit 4.

Reference numeral 4 denotes a comparison circuit which receives the output signal of the input signal conversion circuit 3 and compares it with a comparison reference signal. Reference numeral 5 denotes a comparison reference signal generation circuit.
To generate a plurality of comparison reference signals.

An operation reference signal selection circuit 6 selects and outputs a signal based on the output of the comparison circuit 4. In the comparison reference signal generation circuit 5, reference numeral 10 denotes a comparison reference signal generation unit for generating a plurality of comparison reference signals.

Reference numeral 11 denotes a comparison circuit output signal detection unit.
The output signal of the comparison circuit 4 is detected. Reference numeral 12 denotes a comparison reference signal source.

In the operation reference signal selection circuit 6, reference numeral 15 denotes the operation reference signal source 1. Reference numeral 16 denotes an operation reference signal source 2.

Reference numeral 17 denotes an operation reference signal selector, which selects the operation reference signal source 1 (15) and the operation reference signal source 2 (16) according to the output of the comparison circuit 4. V _EH is the higher supply voltage.

[0021] V _EL is a power supply voltage of the low side. V _M is the comparison input signal of the comparator circuit (comparator input voltage). _VP is a comparison reference signal (comparison reference voltage).

V _H is an H-side output signal (output voltage) of the comparison circuit 4. V _L is an output signal (output voltage) on the L side of the comparison circuit 4.

[0023]

The operation of the configuration shown in FIG. 1 will be described. (1) When the power supply voltage changes from a high voltage to a low voltage.

The comparison circuit 4 outputs V_LIs output. This and
The comparison circuit output signal detection unit 11 _LIs detected and the comparison
The quasi-signal generator 10 outputs the comparison reference signal V_POccurs. this
Comparison reference signal V_PTo V_P’.

The comparison circuit output signal detection section 11 includes a comparison circuit 4
Output V_LIs detected, and the comparison reference signal generation unit 10
The output voltage of the quasi-signal source 12 is compared with the output voltage of
Issue V _P’.

In this state, when the power supply voltage is V_ELDrops to
Then V_MIs V_P′, The comparison circuit 4 outputs V_HTo
Output. Then, in the operation reference signal selection circuit 6,
The operation reference signal selecting section 17 _HIs detected. Soshi
And the proper operation reference signal source 1 (15)
Is selected and output as the operation reference signal.

(2) From a low power supply voltage to a high power supply voltage
If it fluctuates. The output of the comparison circuit 4 is V_HIt is. At this time, the comparison circuit
The force signal detection unit 11 has V _HAnd a comparison reference signal generator
10 is a comparison reference signal V_POccurs.

Then, when the power supply voltage fluctuates to the higher side, V _EH
Becomes, at the V _M = V _P, the comparison circuit 4 outputs a V _L. Then, in the operation reference signal selection circuit 6, the operation reference signal selection section 17 detects the output _VL of the comparison circuit 4. The operation reference signal selection unit 17 selects an appropriate operation reference signal source 2 (16) when the power supply voltage is high, and outputs a signal.

In the above description, the case where the operation reference signal sources (15) and (16) are selected according to the output of the comparison circuit 4 and an appropriate signal is output according to the power supply voltage has been described. The output of the comparison circuit 4 can be directly used as an operation reference signal of the analog circuit 2 '. For example, _{VL of the} comparison circuit 4 is set to about 2 volts, and is used as an operation reference signal when the power supply voltage is low. Alternatively, if the V _H level of the comparison circuit 4 is changed according to the level of the power supply voltage, the V _H signal of the comparison circuit 4 can be used as an operation reference according to the power supply voltage. is there.

According to the present invention, the comparison circuit outputs a signal of a plurality of levels according to the fluctuation of the power supply voltage, and directly inputs the plurality of levels, or selects an appropriate operation reference signal according to the plurality of levels. By doing so, an appropriate operation reference signal can always be obtained.

Further, since the present invention has a hysteresis characteristic as an operation characteristic, the power supply voltage is, for example, V _EH or V
Even if it fluctuates near _EL , it does not affect the output, so a stable output can be obtained.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described by taking as an example a case where the above signal is generated by a voltage signal.

FIG. 2 shows a first embodiment of the present invention. In FIG. 2, reference numeral 20 denotes an operation reference voltage generation circuit.

21 is a power supply voltage. 22 is an analog circuit. 22 'is an analog signal source.

An input voltage conversion circuit 23 includes a resistor R
₁ and the resistor R ₂ divides the power supply voltage Vin min, and outputs the divided voltage V _M. 24 is a comparison circuit,
Inputs the output V _M of the input voltage conversion circuit 23 to the inverting input, the non-inverting input and inputs the reference voltage V _P.

Reference numeral 25 denotes a comparison reference voltage generation circuit which generates a comparison reference voltage. Reference numeral 26 denotes an operation reference voltage selection circuit which selects and outputs an operation reference voltage according to the output of the comparison circuit 24.

[0037] In the input voltage conversion circuit 23, R ₁ is the resistance. R ₂ is the resistance.

In the operation reference voltage generation circuit 20, R ₃
Is a resistance. R ₄ is a resistance. Resistance R ₃ and resistance R ₄
Divides the voltage difference between the output voltage of the comparison circuit 24 and the voltage of the comparison reference voltage source 30 to obtain the comparison reference voltage of the comparison circuit 24.

Reference numeral 30 denotes a comparison reference voltage source, and the voltage V ₁₁
It is. In the operation reference voltage selection circuit 26, reference numeral 31 denotes a switch circuit 1, which is an analog switch circuit composed of a MOSFET or the like.

Reference numeral 32 denotes a switch circuit 2 which is a MOSF.
It is an analog switch circuit configured by ET or the like.
33 is an inverter.

Reference numeral 35 denotes an operation reference voltage source 1, which is a voltage V
₂₁ . Numeral 36 denotes an operation reference voltage source 2 having a voltage V _22.
(V ₂₂ > V ₂₁ ). Vin is a power supply voltage.

Vo is the output voltage of the comparison circuit 24. V
out is the output voltage of the operation reference voltage generation circuit 20.
_VP is a reference voltage of the comparison circuit.

V_MIs the input voltage of the comparison circuit. Of FIG.
The operation of the configuration will be described (see FIG. 3). Fig. 3 (a)
FIG. 4 is a diagram illustrating a relationship between an input voltage and an output voltage of a comparison circuit.
Vin and V _MRelationship, Vin and V_PRelationship (CDEF)
Also shown.

V _EH = 4.0 V, V _EL = 3.0 V, and V _L are the L level of Vo and are about 0 V. V _H , V _H '
Are at the H level. FIG. 3B shows the relationship between the input voltage and the output voltage of the operation reference voltage selection circuit.

In FIG. 2, the comparison circuit 24 satisfies Vo = V _L when V _P > V _M power supply voltage is low and Vo = V _H V _M > V _P power supply voltage is low.

The voltage V of the comparison reference voltage source 30₁₁Is V_H>
V₁₁> V_LAnd (1) When the power supply voltage 21 fluctuates from low to high
Go. From the comparison circuit 24, Vo = V_HIs output. Power supply
Voltage is V_EHWhen V _M= V_EH・ R_Two/ (R₁+
R_Two), V_P= R_Three(V₁₁-V_H) / (R_Three+ R_Four) +
V_H It is.

The power supply voltage fluctuates from low to high, and the output of the comparison circuit 24 changes to V _L at the voltage V _EH (point A in FIG. 3A). At this time, since V _M = V _P , V _EH · R ₂ / (R ₁ + R ₂ ) = R ₃ · (V ₁₁ -V _H ) /
(R ₃ + R ₄ ) + V _H.

Therefore, V_EH= (R₁+ R_Three) ・ R_Two｛V
₁₁・ R_Three/ R_Three+ R_Four) + V_H・ R _Four/ (R_Three+
R_Four)｝.

For example, as shown in FIG.
A), Vin fluctuates from low to high and V _EH =
V _P = V _M becomes at the point A is reached 4.0V, the output of the comparison circuit 4 is changed to V _L.

(2) When the power supply voltage fluctuates from high to low. The comparison circuit 24 outputs Vo = _VL . When the power supply voltage is _{V EL, V M = V EL} · R 2 / (R 1 +
R ₂ ), _VP = R ₃ ( _VL− V ₁₁ ) / (R ₃ + R ₄ ) +
It is V _11.

When the power supply voltage fluctuates from high to low, V
_{When M} = _VP , the output of the comparison circuit 24 changes to _VH . At this _{time, V EL · R 2 / (} R 1 + R 2) = R 3 (V L -V 11) / (R 3 + R 4) is a + V _11.

Therefore, V_EL= ｛(R₁+ R_Two) / R_Two｝ ｛(V₁₁R_Three/ (R_Three
+ R_Four)) + (V_LR _Four/ (R_Three+ R_Four))｝.

This will be described with reference to FIG. Power supply voltage fluctuates high to lower from the side, when Vin reaches V _EL, the output of the V _M = V _P becomes comparator circuit 24 is changed to V _H 'at point B, and outputs the H level.

The operation reference voltage selection circuit 26 operates according to the output of the comparison circuit 24. For example, switch circuit 1 (31)
When Vo is V _H, the switching circuit 2 (32) is turned off, when the switch circuit 1 (31) is turned on, Vo is V _L, the switching circuit 2 (32) is turned on, the switching circuit 1 (31) is turned off So that When the power supply voltage fluctuates from low to high and the power supply voltage becomes V _EH , the output of the comparison circuit 24 becomes _VL ,
The switch circuit 2 (32) is turned on, the switching circuit 1 (31) is turned off, higher voltage V ₂₂ appears at the the Vout. When the power supply voltage fluctuates from high to low and the power supply voltage becomes _VEL , the output of the comparison circuit 24 becomes _VH , the switch circuit 2 (32) is turned off, and the switch circuit 1 (31) is turned on. , V
voltage V ₂₁ of the lower to out appears (see Figure 3 (b)).

FIG. 4 shows a second embodiment of the present invention. Example 2
Is to prepare two types of comparison reference voltage sources and selectively switch the comparison reference voltage sources according to the output logic of the comparison circuit 24.

In FIG. 4, reference numeral 20 denotes an operation reference voltage generation circuit. 21 is a power supply voltage.

Reference numeral 22 denotes an analog circuit. 23 is an input voltage conversion circuit. 25 compares a reference voltage generating circuit has a comparison reference voltage source 1 (41) and the comparison reference voltage source 2 (42), and outputs the reference voltage V _P selectively switching according to the output logic of the comparator circuit 24 Things.

An operation reference voltage selection circuit 26 includes an operation reference voltage source 1 (51) and an operation reference voltage source 2 (52).
The operation reference voltage is selectively output according to the output of the comparison circuit 24.

In comparison reference voltage generation circuit 25, 40
Is a switch circuit 3, which is an analog switch circuit composed of a MOSFET or the like, and is connected between ab or ac according to _VH or _VL of the output of the comparison circuit 24.
The connection is established.

Reference numeral 41 denotes a comparison reference voltage source 1, which is a voltage V
It is ₁₁ . Reference numeral 42 denotes a comparison reference voltage source 2 having a voltage V ₁₂
(V ₁₁ <V ₁₂ ). In the operation reference voltage selection circuit 26, reference numeral 50 denotes a switch circuit 4, which is constituted by an analog switch or the like.
The connection between e and the connection between df are taken.

[0061] In the configuration of FIG. 4, when the Vo = V _H, when _{V P = V 12 Vo = V} L, a V _P = V _11.

However, it is assumed that V ₁₂ > V ₁₁ . The operation of the configuration of FIG. 4 will be described. (1) When the power supply voltage fluctuates from low to high.

V _P is V ₁₂ . The comparison circuit 24 to be a V _M = V _P outputs a V _L. Accordingly, the _{V EH R 2 / (R 1} + R 2) = V 12 V EH = V 12 (R 1 + R 2) / R 2.

[0064] At this time, the switching circuit 3 (40) is set to ab inter connected by the output of the comparator circuit 24 is changed to the V _L, switch the V _P to V _11. (2) If V _P of power supply voltage varies high to lower from the side it is V _11. Then, when it reaches the V _M = V _P, the output of the comparator circuit 24 becomes V _H.

[0065] Thus, the _{V EL R 2 / (R 1} + R 2) = V 11 V EL = V 11 (R 1 + R 2) / R 2.

[0066] At this time, the switching circuit 3 (40) and ac connections by an output of the comparator circuit 24 is changed to the V _H, switches the V _P to V _12. Operation reference voltage selection circuit 2
At 6, the switch circuit 4 (50) is connected between de or df according to the output of the comparison circuit 24, and the power supply voltage fluctuates from low to high, so that the output of the comparison circuit 24 becomes _VL . since when, and outputs the V ₂₂ as df connections.
Power supply voltage fluctuates high to lower from the side, when the output of the comparator circuit 24 becomes V _H, and outputs the V ₂₁ as de connections.

Note that V ₂₁ <V ₂₂ . FIG. 5 shows an example of the comparison circuit of the present invention. The comparison circuit of FIG.
It is composed of an active load and a current mirror circuit.

In FIG. 5, reference numeral 24 denotes a comparison circuit. 6
0 is a differential amplifier circuit.

T ₁ , T ₃ and T ₅ are P-type MOSFETs. T ₂ , T ₄ , T ₆ , T ₇ , T ₈ are N-type MOSFETs
It is. R is a resistance.

The operation of FIG. 5 will be described. (1) When V _P = V _{M , set} V _O = (V _DD + V _SS ) / 2. That is, previously set to be on-resistance of the on resistance = T ₂ T _1. VA at this time is set to _VA0 .

[0071] (2) on-resistance of T ₆ is reduced when the V _P> V _M, become a VA <VA _0, T ₁
And the ON resistance of T < ₂ , and Vo becomes the H level.

[0072] (3) <on-resistance of the T ₆ is raised when the V _M, VA> V _P become a VA _0, T ₁
Becomes on-resistance> T ₂ on-resistance, Vo becomes the L level.

[0073] with respect to T _3, T ₅ constitute a current mirror circuit. Even when the current of T ₃ at a temperature change or the like varies, the current of T ₅ varies in the same way. FIG. 6 shows an example of an analog switch circuit used in the present invention.

In FIG. 6, T ₁ is a P-type MOSFET. T ₂ are an N-type MOSFET.

T ₃ is a P-type MOSFET. T ₄ is N
Type MOSFET. VDD is a power supply voltage.

VSS is a ground voltage. In the configuration of FIG. 6, when S is H, conduction is made between BC. A when S is L
C is connected. When applied to the present invention, the comparison circuit output Vo is input to S. A comparison reference voltage source or an operation reference voltage source is connected between A and B.

[0077]

According to the present invention, the operation reference signal is automatically changed according to the fluctuation of the power supply voltage, and an appropriate operation reference signal is always output. Further, since the present invention has a hysteresis characteristic, the switching operation is not performed with respect to the fluctuation of the power supply voltage, and the operation reference signal can be stably output.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a first embodiment of the present invention.

FIG. 3 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing an example of a comparison circuit used in the present invention.

FIG. 6 is a diagram showing an example of an analog switch used in the present invention.

FIG. 7 is an explanatory diagram of a conventional technique.

FIG. 8 is an explanatory diagram of means for solving the problem.

[Explanation of symbols]

 1: operation reference signal generation circuit 2: power supply voltage 2 ': analog circuit 3: input signal conversion circuit 4: comparison circuit 5: comparison reference signal generation circuit 10: comparison reference signal generation unit 11: comparison circuit output signal detection unit 12: Comparison reference signal source

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-43408 (JP, A) JP-A-2-272810 (JP, A) JP-A-3-228409 (JP, A) JP-A-5-208 335840 (JP, A) JP-A-59-141823 (JP, A) JP-A-3-92828 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03G 3/02 H03G 3 /Ten

Claims (9)

(57) [Claims] An input signal conversion circuit for inputting a power supply voltage and converting an input voltage, an output of the input signal conversion circuit being input as a first input signal, and a comparison reference signal being input as a second input signal A comparison circuit for comparing the first input signal with the second input signal, a comparison reference signal generation circuit for generating the comparison reference signal, and an analog circuit according to an output of the comparison circuit. And an operation reference signal selection circuit for outputting operation reference signals of different levels. The comparison reference signal generation circuit detects an output of the comparison circuit, and outputs the output of the comparison circuit. If the first input signal is larger than the second input signal, a first reference signal is generated as the comparison reference signal, and the output of the comparison circuit is the output of the first input signal. Is smaller than the second input signal. A second reference signal which is larger than the first reference signal as the comparison reference signal. 2. The comparison circuit according to claim 1, wherein the comparison circuit comprises an operational amplifier, an output of the input signal conversion circuit is input to an inverting input of the operational amplifier, and the comparison reference signal is connected to a non-inverting input terminal. A signal generation circuit characterized in that: 3. The comparison circuit according to claim 1, wherein the comparison circuit includes a differential amplifier circuit, an active load of the differential amplifier circuit, and an active element that forms a current mirror circuit with respect to the active load. A signal generation circuit characterized in that: 4. The signal generation circuit according to claim 1, wherein said input signal conversion circuit converts the amplitude of an input signal. 5. The method according to claim 1, 2, 3, or 4,
The comparison reference signal generation circuit includes a comparison reference signal source and a comparison reference signal generation unit, detects an output signal of the comparison circuit, and generates a comparison reference signal based on the output signal and the signal of the comparison reference signal source. A signal generating circuit for outputting. 6. The comparison reference signal according to claim 1, wherein the comparison reference signal generation section performs voltage division conversion on a difference between an output signal of the comparison circuit and a signal of the comparison reference signal source. And a signal generation circuit for generating a signal. 7. The comparison reference signal generation circuit according to claim 1, wherein the comparison reference signal generation circuit includes a plurality of comparison reference signal sources, and wherein the comparison reference signal generation section performs different comparison according to an output of the comparison circuit. A signal generation circuit for selecting a reference signal source and outputting a different comparison reference signal. 8. The signal generation circuit according to claim 1, wherein said operation reference signal selection circuit includes a plurality of operation reference signal sources. 9. The comparison reference signal generation circuit or the operation reference signal selection circuit according to claim 7, further comprising an analog switch circuit responsive to the output of the comparison circuit, wherein the comparison reference signal source or the operation reference signal source is responsive to the output of the comparison circuit. A signal generation circuit for selecting an operation reference signal source.