JP4204103B2 - Integration circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an integration circuit suitable for use in a filter circuit or the like, and is particularly configured to reduce an occupied area on a semiconductor integrated circuit and obtain a high DC gain.
[0002]
[Prior art]
Conventionally, as one of the filter circuits, there is one in which a desired current characteristic is obtained by combining a voltage-current conversion circuit and an integrating circuit using a capacitor. In this type of filter circuit, particularly when realizing a filter characteristic with a high Q value, there is a problem that a deviation from the ideal characteristic of the amplitude / phase characteristic of the integrating circuit deteriorates the filter characteristic.
[0003]
As a method of improving the deviation of the amplitude / phase characteristics of the integrating circuit and bringing it closer to the ideal characteristic, there is a configuration in which the input / output of the integrating circuit is a differential type that is differential. In this case, a common-mode feedback circuit for determining the operating potential of the integrator circuit output is required. As an example of an integrating circuit having such an in-phase feedback circuit, one disclosed in Japanese Patent Laid-Open No. 5-14119 is known.
[0004]
In the conventional integrating circuit shown in FIG. 5, the mutual conductance circuit including the transistors Q1 and Q2 has a base as an input terminal and a commonly connected emitter connected to the current source I1. The collectors of the transistors Q1 and Q2, which are current output terminals, are connected to the collectors of the transistors Q3 and Q4 constituting the variable current source and the bases of the transistors Q6 and Q7, and the integration capacitors are respectively connected between the current output terminal and the power source Vcc. C1a and C1b are connected. The transistors Q6 and Q7 are so-called emitter follower circuits in which current sources I2 and I3 are connected to the respective emitters. By connecting equal resistors R1 and R2 in series between the emitters, the midpoint from the connection point between the two resistors Getting voltage.
[0005]
The midpoint voltage is compared with the reference voltage Vref by a comparison circuit comprising a transistor pair Q8, Q9 having a current source I4 connected to a common emitter. The compared output is output as a current from the collector of the transistor Q9 to the diode-connected transistor Q5. The diode-connected transistor Q5 is connected between the bases of the transistors Q3 and Q4 and the power source Vcc to form a current mirror circuit, and the currents of the transistors Q3 and Q4 are controlled so that the midpoint voltage and the reference voltage Vref are equal. The operating potential of the integrating circuit is determined.
[0006]
[Problems to be solved by the invention]
However, in the above-described conventional integrating circuit, a resistor is connected in series to obtain the midpoint voltage between the emitters of the emitter follower circuit connected to the current output terminal of the mutual conductance circuit. In order to increase the resistance, there is a problem that the resistance value increases, and the occupied area increases when the semiconductor integrated circuit is configured.
[0007]
Further, as shown in FIG. 6, in order to operate the integration circuit with a lower power supply voltage, when there is no emitter follower circuit connected to the current output terminal, a resistor for obtaining the midpoint voltage is a current output. Since it is directly connected to the end, it is necessary to increase the resistance value, and there is a problem that the occupied area on the semiconductor integrated circuit increases.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described conventional problems, and to provide an integration circuit having a high DC gain while reducing the occupied area on a semiconductor integrated circuit.
[0009]
[Means for Solving the Problems]
In order to solve the above problem, the present invention provides a first comparison unit that outputs a potential difference between one potential of a differential output terminal of a voltage-current conversion circuit and a reference potential as a current, and a potential difference between the other potential and the reference potential. The second comparison means for outputting the current as a current is provided, the output currents of the two comparison means are added, and the in-phase potential at the differential output terminal is controlled to be equal to the reference potential.
[0010]
This eliminates the need for a resistor for detecting the midpoint potential of the differential output terminal, thereby reducing the occupied area on the semiconductor integrated circuit and providing an integration circuit with a high DC gain.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
According to a first aspect of the present invention, there is provided a voltage-current conversion circuit in which a variable current source is connected to each of differential output terminals, and a potential difference between one potential of the differential output terminals and a reference potential is output as a current. 1 comparison means, second comparison means for outputting a potential difference between the other potential of the differential output terminal and the reference potential as a current, and output currents of the first comparison means and the second comparison means. And a current control means for controlling the amount of current of the variable current source so that the in-phase potential of the differential output terminal is equal to the reference potential, and at least a capacitor connected between the differential output terminal and the ground. The integrating circuit is provided, and has the effects of reducing the occupied area on the semiconductor integrated circuit and obtaining a high DC gain.
[0012]
According to a second aspect of the present invention, the first comparison unit and the second comparison unit include a first differential pair and a second differential pair having emitters connected in common. The variable current source and the current control means comprise transistors constituting a current mirror circuit, and both the potential at the differential output terminal and the reference potential are respectively sent to the first and second differential pairs via an emitter follower. The integration circuit according to claim 1, wherein the integration circuit is inputted, and has an effect of reducing an occupied area on the semiconductor integrated circuit and obtaining a high DC gain.
[0013]
The invention according to claim 3 is characterized in that both the potentials of the differential output terminals and the reference potential are inputted to the bases of the first and second differential pairs. This has an effect of reducing the occupied area on the semiconductor integrated circuit and obtaining a high DC gain even in operation with a lower power supply voltage.
[0014]
According to a fourth aspect of the present invention, an emitter follower is connected to the input of the voltage / current converter, and a transistor is inserted between the output of the voltage / current converter and the variable current source to form a cascade connection. The integration circuit according to claim 2, wherein the area occupied on the semiconductor integrated circuit is reduced and a high DC gain is obtained. Further, the input / output impedance of the integrating circuit can be increased.
[0016]
According to a fifth aspect of the present invention, a filter circuit is configured using the integrating circuit according to any one of the first to fourth aspects, and the area occupied on the semiconductor integrated circuit can be reduced. Have
[0017]
The invention according to claim 6 is the one in which the filter circuit according to claim 5 is provided in the transmission unit or the reception unit of the wireless communication apparatus, and has an effect that the apparatus can be miniaturized.
[0018]
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0019]
(First embodiment)
In the integrating circuit according to the first embodiment of the present invention shown in FIG. 1, the voltage-current converter circuit 1 has a positive input terminal 2 and a negative input terminal 3 to which input voltage signals are input and a positive current output terminal. Current is output from the side output terminal 4 and the negative output terminal 5. Integration capacitors 10 and 11 are connected to the positive output terminal 4 and the negative output terminal 5 between the collectors of the transistors 6 and 7 constituting the variable current source, the bases of the transistors 8 and 9 and the power source Vcc, respectively. . The transistors 8 and 9 are so-called emitter follower circuits in which current sources 12 and 13 are connected to the respective emitters.
[0020]
The potential of the positive output terminal 4 is output from the emitter of the transistor 8 and input to the base of the transistor 15 of the comparison circuit including the transistor pairs 15 and 16 in which the current source 14 is connected to the common emitter.
[0021]
The potential of the negative output terminal 5 is output from the emitter of the transistor 9 and input to the base of the transistor 18 of the comparison circuit including the transistor pairs 17 and 18 in which the current source 19 is connected to the common emitter.
[0022]
The reference voltage Vref is input to the base of a transistor 21 constituting an emitter follower by connecting a current source 20 to the emitter, and the emitter of the transistor 21 is connected to the bases of the transistors 16 and 17.
[0023]
Current is output from the respective collectors of the transistor pairs 15 and 16 according to the potential difference between the positive output terminal 4 and the reference voltage Vref, and the transistor pairs 17 and 18 according to the potential difference between the negative output terminal 5 and the reference voltage Vref. Current is output from each of the collectors.
[0024]
The collectors of the transistors 15 and 18 are connected to the power supply Vcc. The collectors of the transistors 16 and 17 are connected to a diode-connected transistor 22. The diode-connected transistor 22 is connected between the bases of the transistors 6 and 7 and the power source Vcc to form a current mirror circuit.
[0025]
As an example, the voltage-current conversion circuit 1 may be a transistor pair in which a current source is connected to a common emitter, but other voltage-current conversion circuits may be used.
[0026]
Here, when the transistor pair 15 and 16 and the transistor pair 17 and 18 are the same circuit, and the current source 14 and the current source 19 have the same current value, the positive output terminal 4 and the negative output terminal 5 For the differential potential, the increase and decrease of the collector currents of the transistors 16 and 17 cancel each other, and the current flowing through the transistor 22 does not change.
[0027]
On the other hand, with respect to the common-mode potential of the positive output terminal 4 and the negative output terminal 5, the current flowing through the transistor 22 changes according to the potential difference from the reference voltage Vref, and negative feedback is applied. The currents of the transistors 6 and 7 are controlled so that the common-mode potential of the negative output terminal 5 is equal to the reference voltage Vref, and the operating potential of the integrating circuit is determined.
[0028]
The difference from the conventional example shown in FIG. 5 is that there is no series-connected resistance for obtaining a midpoint voltage between the emitters of the emitter follower circuit connected to the differential output terminal of the voltage-current converter circuit 1. . The output of each emitter follower circuit is connected to the base of a comparison circuit composed of a transistor pair, and since the input impedance is high, the DC gain of the integration circuit can be increased.
[0029]
(Second Embodiment)
FIG. 2 shows a configuration of an integration circuit according to the second embodiment of the present invention. The difference from the integration circuit of FIG. 1 is that there is no emitter follower circuit composed of transistors 8, 9, and 21 and current sources 12, 13, and 20. The potential of the positive output terminal 4 The signal is input to the base of the transistor 15 of the comparison circuit including the transistor pair 15 and 16 connected to the source 14. The potential of the negative output terminal 5 is input to the base of the transistor 18 of the comparison circuit including the transistor pair 17 and 18 in which the current source 19 is connected to the common emitter. The reference voltage Vref is connected to the bases of the transistors 16 and 17.
[0030]
The difference from the conventional example shown in FIG. 6 is that there is no series-connected resistor for obtaining a midpoint voltage between the differential output terminals of the voltage-current converter circuit. The output of the voltage-current conversion circuit 1 is connected to the base of a comparison circuit composed of a transistor pair, and since the input impedance is high, the effect that the DC gain of the integration circuit can be increased is obtained. Further, since there is no emitter follower, an effect is obtained that the integration circuit can operate even at a lower power supply voltage.
[0031]
(Third embodiment)
FIG. 3 shows the configuration of the integrating circuit according to the third embodiment of the present invention. 1 differs from the integration circuit of FIG. 1 in that an emitter follower circuit in which current sources 33 and 34 are connected to the emitters of the transistors 31 and 32 is connected to the input of the voltage-current conversion circuit 1, and each output of the voltage-current conversion circuit 1 is further connected. The transistors 35 and 36 are inserted between the collectors of the transistors 6 and 7 constituting the variable current source to form a cascade connection, and a voltage source 37 connected to the bases of the transistors 35 and 36 is provided. Thereby, the effect that the input / output impedance of the integration circuit can be further increased can be obtained.
[0032]
(Fourth embodiment)
FIG. 4 shows a band-pass filter circuit as an example of a filter circuit configured by using the integrating circuit according to the fourth embodiment of the present invention. The band-pass filter circuit includes voltage-current conversion circuits 101, 102, 103, 104 and capacitors 105, 106, 107, 108.
[0033]
The transconductances of the voltage-current conversion circuits 101 to 104 are gm1 to gm4, respectively, the capacitance value corresponding to the balance line of the capacitors 105 and 106 connected to the outputs of the voltage-current conversion circuits 102 and 104 is Ca, and the voltage-current conversion circuit 103 Assuming that the capacitance value corresponding to the balanced line between the capacitors 107 and 108 connected to the output of Cb is Cb, the transfer function H (s) of this filter can be expressed by the following equation (1).
H (s) = (s · gm1 / Ca) ÷
(s ^ 2 + s · gm4 / Ca + gm2 · gm3 / (Ca · Cb)) (1)
[0034]
If such a filter circuit is configured using an integrating circuit with a high DC gain, a high Q value filter characteristic can be obtained without increasing the occupied area on the semiconductor integrated circuit. When this filter circuit is applied to a filter circuit of a transmission unit or a reception unit in a wireless communication device having a transmission / reception unit, the wireless communication device can be reduced in size. Therefore, the wireless communication device can be provided with high performance and low cost.
[0035]
In the above description, the integration capacitor is described as an example in which the integration capacitor is connected between the differential output terminal of the voltage-current converter circuit and the power source Vcc. However, the integration capacitor is integrated between the differential output terminal of the voltage-current converter circuit. A capacity may be connected.
[0036]
In the above description, an example in which the transistor is a bipolar transistor has been described. However, the present invention can be similarly applied to a transistor using another semiconductor process such as a MOS transistor.
[0037]
In the above description, the band-pass filter circuit shown in FIG. 4 is described as an example of the filter circuit. However, the present invention is not limited to this. Any device can be used as long as it has characteristics.
[0038]
【The invention's effect】
As described above, the present invention provides a comparing means for canceling the differential potential at the differential output end of the integrating circuit and outputting only the common-mode potential as a current, and a resistor for detecting the midpoint potential of the differential output end. Therefore, the area occupied on the semiconductor integrated circuit can be reduced, and the DC gain of the integrating circuit can be increased.
[0039]
Further, if a filter circuit is configured using such an integration circuit, a high Q value filter characteristic can be obtained without increasing the occupied area on the semiconductor integrated circuit.
[0040]
Furthermore, by incorporating this filter circuit in the transmitter or receiver of the wireless communication device, the wireless communication device can be reduced in size.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an integrating circuit according to a first embodiment of the present invention;
FIG. 2 is a block diagram showing a configuration of an integration circuit in the second embodiment of the present invention;
FIG. 3 is a block diagram showing a configuration of an integrating circuit according to a third embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of a bandpass filter circuit using an integration circuit according to a fourth embodiment of the present invention;
FIG. 5 is a block diagram showing a configuration of a conventional integrating circuit;
FIG. 6 is a block diagram showing a configuration of another conventional integration circuit.
[Explanation of symbols]
1 Voltage-current conversion circuit 6, 7, 22, 35, 36 PNP transistor 8, 9, 15-18, 21 NPN transistor
31, 32 NPN transistor
10, 11 capacity
12-14, 19, 20, 33, 34 Current source
101-104 Voltage-current converter R1, R2 Resistors C1a, C1b Capacitance Vref Reference voltage Vcc Power supply I1-I4 Current source

Claims (6)

  A voltage-current conversion circuit in which a variable current source is connected to each of the differential output terminals; first comparison means for outputting a potential difference between one potential of the differential output terminals and a reference potential as a current; and A second comparing means for outputting a potential difference between the other potential and the reference potential as a current; and adding the output currents of the first comparing means and the second comparing means to obtain an in-phase potential at the differential output terminal; An integrating circuit comprising: current control means for controlling a current amount of the variable current source so that the reference potentials are equal; and a capacitor connected at least between the differential output terminal and the ground.   The first comparing means and the second comparing means are composed of a first differential pair and a second differential pair having emitters connected in common, and the variable current source and the current control means are current mirrors. 2. The circuit according to claim 1, comprising a transistor constituting a circuit, wherein both the potential of the differential output terminal and the reference potential are input to the first and second differential pairs via an emitter follower, respectively. Integration circuit.   3. The integration circuit according to claim 2, wherein both the potential of the differential output terminal and the reference potential are input to bases of the first and second differential pairs.   3. An integrating circuit according to claim 2, wherein an emitter follower is connected to an input of the voltage-current converter circuit, and a transistor is inserted between the output of the voltage-current converter circuit and the variable current source to form a cascade connection. . Filter circuit characterized by comprising an integrating circuit according to any one of claims 1 to 4, wherein. A wireless communication apparatus comprising the filter circuit according to claim 5 in a transmission unit or a reception unit.

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