JPH0969752A - Filter circuit and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a circuit scale and to realize a wide dynamic range with a low minimum operation voltage by connecting a capacitor, which takes out a signal component in a prescribed band, in series to first and second specific diodes. SOLUTION: A primary filter 24 has a first differential pair consisting of a first transistor TR Q1 and a TR Q2 as a first diode and a second differential pair composed of a second TR Q2n and a TR Q2n-1 as a second diode. A capacitor C which takes out the signal component in the prescribed band from both ends is connected in series to the first diode Q2, which is always made conductive by a second current source 26 only for diode, of the first differential pair, to which one of differential input signals is given, and the second diode Q2n-1, which is always made conductive by a fourth current source 28 only for diode, of the second differential pair to which the other signal is given.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. TECHNICAL FIELD The invention belongs to the related art Problem to be solved by the invention Means for solving the problem Embodiments of the invention (1) Secondary filter (1-1) Basic configuration (primary filter) (1-2) State variable filter (secondary filter) (2) Dynamic range expansion type primary filter according to the embodiment (2-1) Basic configuration (2-2) Low power supply voltage compatible primary filter (2-3) Low Power consumption type primary filter (3) Application device example (4) Other embodiments Effect of the invention

[0002]

TECHNICAL FIELD The present invention relates to a filter circuit. In particular, it is suitable for use in those requiring low voltage operation and a wide dynamic range.

[0003]

2. Description of the Related Art FIG. 9 shows a circuit example of a primary low-pass filter, and FIG. 10 shows the configuration of a differential integrator used in this primary filter. The differential integrator 1 is composed of a differential input stage and a differential output stage. The differential input stage is
Transistors Q1 and Q2 of the differential pair, Dyna and Mitsu click range to expand the two resistors R1, is composed of a constant current source 2 supplies a constant current I ₁ to the differential pair, the differential current input voltage V _IN Convert to.

The differential output stage differentially supplies a reference voltage source Vref, diodes D1 and D2, differential pair NPN type transistors Q3 and Q4, load PNP type transistors P1 and P2, and a constant current I ₂ . A Gilbert multiplier is constituted by a constant current source 3 supplied to the pair. Differential output stage generates a differential output currents ± i ₀ amplifies the differential current obtained from the differential input stage, charging the differential output currents ± i ₀ to each of the one end of the two capacitors C To discharge. As a result, the output voltage V ₀ is taken out between the ends of the two capacitors C.

At this time, the voltage-current conversion coefficient gm of the differential integrator 1 is given by

[Equation 1] Given in. The output voltage V _O is given by

[Equation 2] It can be expressed as. Accordingly, the transfer function H (= V _O / V _IN ) of the first-order low-pass filter shown in FIG.

(Equation 3) Given in.

[0006]

However, the above-mentioned conventional primary filter requires the common mode feedback circuit 4 in order to stabilize the collector voltage of the transistors Q3 and Q4. In addition, the number of elements in the entire primary filter is large and the chip area becomes large. Similarly, a secondary filter could not avoid the same problem by requiring multiple primary filters as described above with an integrator (1 / s).

By the way, in recent years, it has been desired to use electronic equipment with a low-voltage power source using a small battery. Therefore, it is desired that the filter used in the electronic device can be used with a low power supply voltage. However, the above-mentioned primary filter is used in the common mode feedback circuit 4
And the transistors P1 and P2 and the transistors Q3 and Q4 are connected in series to the power supply.
For this reason, there is a problem in that it is difficult to sufficiently cope with use at a low power supply voltage.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a filter circuit which can be downsized in circuit scale, has a low minimum operating voltage and a wide dynamic range, and an electronic device using the same. It is a thing.

[0009]

In order to solve the above problems, in the present invention, a first transistor to which one input signal of a differential input signal is applied to an input terminal, and an emitter of the first transistor are connected in series. At least a first differential pair, which is connected and includes a first diode that differentially operates with a first transistor, and is interposed between an emitter of the first transistor and a first power supply, A first current source that drives the transistor, a second current source that is interposed between the first diode and the second power source and that keeps the first diode conductive, and a differential input signal A second differential pair including a second transistor to which the other input signal is applied, a second diode connected in series with an emitter of the second transistor and differentially operating with the second transistor; Tran of 2 A third current source interposed between the emitter of the star and the first power source to drive at least the second transistor; and a second current source interposed between the second diode and the second power source. A fourth current source that always conducts a diode and a first and a second diode are connected in series between the respective emitters of the first and second transistors,
A capacitor for extracting a signal component in a predetermined band from both ends is provided.

A capacitor for extracting a signal component of a predetermined band from both ends is always made conductive by a second current source dedicated to a diode of the first differential pair to which one input signal of the differential input signal is applied. By connecting in series with the first diode which is always on and the second diode which is always conducted by the fourth current source dedicated to the diode of the second differential pair to which the other input signal is applied. It is possible to realize a filter circuit which has a smaller circuit scale, a lower minimum operating voltage than that of the conventional one, and a wider dynamic range, and an electronic device using the same.

Further, according to the present invention, in an electronic device having a processing circuit for performing signal processing based on a signal component of a predetermined band extracted in a filter circuit given a differential input signal, the filter circuit is provided with a differential signal at an input terminal. A first transistor supplied with one of the input signals;
A first differential pair, which is connected in series with the emitter of the first transistor and includes a first diode that operates differentially with the first transistor, and an emitter between the emitter of the first transistor and the first power supply. A first current source that is inserted to drive at least the first transistor, a second current source that is interposed between the first diode and the second power source, and that always conducts the first diode, and an input A second transistor including a second transistor whose terminal receives the other input signal of the differential input signal and a second diode which is connected in series with the emitter of the second transistor and differentially operates with the second transistor. A differential pair, a third current source interposed between the emitter of the second transistor and the first power source to drive at least the second transistor, a second diode and a second power source. Interpolated between the first 4 to the diodes always conduct
And a capacitor connected in series with the first and second diodes between the respective emitters of the first and second transistors and extracting a signal component in a predetermined band from both ends.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

(1) Secondary Filter (1-1) Basic Configuration (Primary Filter) In FIG. 1 in which parts corresponding to those in FIG. 10 are designated by the same reference numerals, 5 indicates a primary filter as a whole, and It is used for the secondary filter according to the invention. The primary filter 5 is composed of a differential pair, a diode, a current source, and a capacitor. The primary filter 5 outputs a differential signal S1 having a high-pass characteristic from the midpoint of connection between the differential pair and the diode. In addition, the primary filter 5 outputs a differential signal S2 having a low-pass characteristic from the midpoint of connection between the differential pair and the current sources 6 and 7 that drive the differential pair.

Next, a concrete configuration of each of these parts will be described. The differential pair includes a pair of transistors Q1 and Q2, and a differential signal S3 is provided at the bases of the transistors Q1 and Q2.
Is entered. The diode is a so-called diode-connected transistor Q3 whose base and collector are short-circuited.
And Q4, and the respective emitters of the transistors Q3 and Q4 are connected to the collectors of the transistors Q1 and Q2 of the differential pair. The collectors of the transistors Q3 and Q4 are connected to the power supply voltage V _CC .

The current sources consist of constant current sources 6 and 7. The constant current sources 6 and 7 are interposed between the respective emitters of the transistors Q1 and Q2 of the differential pair and the ground line GND, and supply the constant current I ₁ to the transistors Q1 and Q2, respectively. The capacitor C is connected between the emitters of the transistors Q1 and Q2 that form a differential pair.

It will be described that, in the above-mentioned configuration, the output of each frequency characteristic is obtained from each output terminal of the primary filter 5. First, it will be explained that the low-pass filter characteristic can be obtained. Now, when the differential signal S3 of the difference voltage V _IN is input, the current i _L flows through the capacitor C. If the emitter resistance of the transistors Q1 and Q2 of the differential pair is re (= V _T / I), the current i _L is given by the following equation.

(Equation 4) Is required.

Therefore, the differential voltage V _L generated between the emitters of the transistors Q1 and Q2 is

(Equation 5) Is required. At this time, if 1/2 re C is set to ω c, the ratio between the difference voltage V _IN and the difference voltage V _L is

(Equation 6) Becomes From the above, it can be seen that the differential signal S2 having the primary low-pass filter characteristic with the cut-off frequency fc being ωc / 2π can be obtained from the midpoint of connection between the differential pair and the current source.

Next, it will be explained that a high pass filter characteristic is obtained. Now, assuming that the current amplification factor β is infinite, the current i _H flowing through the transistors Q3 and Q4 when the differential signal S3 of the difference voltage V _IN is input becomes equal to the current i _L. At this time, the differential voltage V _H of the differential signal S1 generated in the collectors of the transistors Q1 and Q2 is

(Equation 7) Is required.

Therefore, when the ratio of the difference voltage V _IN and the difference voltage V _H is calculated, the following equation is obtained.

(Equation 8) Is obtained. From the above, it can be seen that it is possible to obtain the differential signal S1 having the primary high-pass filter characteristic in which the cutoff frequency fc is ωc / 2π from the midpoint of connection between the differential pair and the diode. Incidentally, the value of the emitter resistance re can be adjusted according to the current I ₁ supplied by the constant current sources 6 and 7. This allows the cutoff frequency fc to be adjusted arbitrarily.

According to the above structure, since the NPN type transistor can be used alone, a primary filter requiring a much smaller number of manufacturing processes than the conventional one can be realized. Further, since all the signals in the circuit are differential signals, it is possible to realize a primary filter that is less likely to be affected by power supply voltage fluctuations and external noise. Further, since it is not necessary to provide the common mode feedback circuit 4 unlike the conventional type filter, the circuit structure can be further downsized, and a primary filter can be realized in which the number of elements can be further reduced.

(1-2) State Variable Filter (Secondary Filter) Next, the circuit configuration of the secondary filter will be described. 2 is 2
The block configuration of the next filter 8 is shown. The secondary filter 8 is constructed by combining the primary low-pass filter locks L1 and L2 obtained from the primary filter 5 described in the previous section and the primary high-pass filter locks H1, H2 and H3. Incidentally, ωc / (s + ωc) shown in FIG.
The block of represents the primary low-pass filter, s / (s +
The block of ωc) represents the first-order high-pass filter. A1 and A2 represent an A1 times amplifier and an A2 times amplifier, respectively.

In the above construction, the secondary filter 8 has three
It will be explained that a secondary filter having various kinds of outputs is provided.
First, the two-stage primary low-pass filter blocks L1 and L2
It will be described that the characteristic of the output signal output via the signal becomes the secondary low-pass filter characteristic. Now, assuming that the output voltage of the adder is V _A and the output voltage of the primary low-pass filter block L2 is V _L , the two output voltages V _A and V _L are

[Equation 9]

(Equation 10) Holds.

Substituting equation (9) into equation (10),
Next formula

[Equation 11] Relationship is obtained. When the transfer function H _L is obtained from this equation (11),

(Equation 12) It can be seen that the secondary low-pass filter characteristic is obtained as shown in FIG. The resonance angular frequency ω ₀ and quality actor Q are
Next formula

(Equation 13)

[Equation 14] Given in. From this, it is understood that these values can be adjusted by adjusting the gain of the amplifier A2.

Similarly, the primary low-pass filter block L1
And the transfer function H _B is obtained with the output voltage output via the first-order high-pass filter block H1 as V _B.

(Equation 15) Becomes From these, it can be seen that the output voltage V _B has the secondary band pass filter characteristic. Incidentally, the resonance angular frequency ω ₀ and the quality actor Q are the same as the expressions (13) and (14), respectively.

Similarly, when the output voltage output through the two-stage primary high-pass filter blocks H2 and H3 is V _H and its transfer function H _H is obtained,

(Equation 16) Therefore, it can be seen that the secondary high-pass filter characteristic is obtained. A concrete circuit configuration example of the secondary filter 8 having this characteristic is shown in FIGS. The circuit shown in FIG. 3 is different from the circuit shown in FIG. 4 in that the former uses NPN type bipolar transistors as transistors and the latter uses N-channel field effect transistors.

The circuits shown as specific examples have five circuits, respectively.
It is configured by one block B1 to B5. Blocks B2 to B4 are primary filters, which are shown in FIG.
It is constructed similarly to the next filter 5. The block B2 is the primary low-pass filter block L1 shown in FIG.
It also corresponds to the primary high-pass filter block H2. The block B3 corresponds to the primary high-pass filter block H3 shown in FIG. The block B4 corresponds to the primary low-pass filter lock block L2 and the primary high-pass filter lock block H1 shown in FIG. Block B1
Corresponds to the amplifier A1 and the adder. Block B5
Corresponds to the amplifier A2.

The block B5 draws a differential current having a magnitude corresponding to the output of the low-pass filter block L2 from the midpoint of connection between the differential pair of the block B1 and each load resistor R2. As a result, block B5
This means that a voltage obtained by adding a voltage obtained by multiplying the input voltage V _IN by A1 and a voltage obtained by multiplying the output voltage V _L by A2 is generated in the resistor R2.

Incidentally, in the case of this circuit configuration, the gain G1 of the amplifier A1 becomes R2 / (R1 + V _T / I _A ) and the gain G2 of the amplifier A2 becomes R2 // (R3 + V _T / I _A ).
Of the parameters that give .omega.c (= 1/2 re C), the emitter resistance re is V _T / I _F. Thus, by adjusting the value of the constant current I _F , the resonance angular frequency ω ₀ is maintained while the value of the quality actor Q is kept constant.
Only can be adjusted.

According to the above configuration, since the secondary filter 8 can be constructed only by the primary filter 5 described in the previous section, the circuit configuration can be improved as compared with the conventional filter constructed by using the integrator 1. The size can be further reduced, and the number of elements can be further reduced. Further, since the secondary filter 8 is composed of a differential circuit,
Hardly affected by power supply voltage fluctuations and external noise. Furthermore NP
Since the circuit can be composed of only N-type transistors, the manufacturing process can be further simplified as compared with the conventional one.

(2) Dynamic Range Expanding Type Primary Filter According to the Embodiment (2-1) Basic Structure Next, a primary filter in which the dynamic range is expanded n times as much as the primary filter 5 of FIG. A configuration example is shown in FIG. This primary filter 20 also has the basic configuration shown in FIG.
Similar to the next filter 5, a differential pair, a diode,
It is composed of four elements, a current source and a capacitor.

There are two differences. The first difference is that the diode-connected n−2 transistors Q2 and Q21
... Qn and Qn1 are transistors Q forming a differential pair
That is, they are connected in series between the emitters 1 and Q11 and the constant current sources 21 and 22. The second difference is that
The constant current sources 21 and 22 supply a current nI which is n times as large as that of the constant current sources 6 and 7 of FIG. 1 to the transistors Q1 and Q1 of the differential pair.
1 to supply each.

Referring to the equation (5), the transfer function H (= V _O / V _IN ) of the primary filter 20 is obtained by comparing the bases of the transistors Q1 and Q11 forming the differential pair with the capacitor C. Since the number of emitter resistors re connected between the two is n, respectively,

[Equation 17] Becomes Incidentally, the value of each emitter resistance re is V _T
/ NI. By substituting this value into Eq. (17),

(Equation 18) Therefore, it can be seen that the low pass filter characteristic is exhibited.

By the way, the value of the parameter V _T / I giving the value of ωc 'in the equation (18) is the same as the emitter resistance re in the circuit of FIG. From this, it can be seen that ωc ′ of the primary filter 20 shown in FIG. 5 and ωc of the primary filter 5 shown in FIG. 1 have the same value. Therefore, the cutoff frequencies fc of the primary filter 5 and the primary filter 20 are the same. That is, the transistor Q forming the differential pair
Primary filter 20 except that the number of emitter resistors re connected between the respective bases of 1 and Q11 and capacitor C is n times that of primary filter 5, resulting in n times the dynamic range. It can be seen that the other characteristics of are the same as those of the primary filter 5.

According to the above construction, the primary filter 2 has a dynamic range n times larger than that of the primary filter 5 of FIG.
You can get 0. Further, like the above-described primary filter 5, the primary filter 20 can be configured by only NPN type transistors, so that the manufacturing process can be further simplified as compared with the conventional one. Further, since the primary filter 20 is composed of a differential circuit, it has a characteristic that it is unlikely to be affected by power supply voltage fluctuations and external noise. Further, unlike the conventional filter, the common mode feedback circuit 4 need not be provided.
The circuit configuration can be further downsized, and the number of elements can be further reduced.

(2-2) Primary Filter for Low Power Supply Voltage Next, the primary filter 5 shown in FIG. 5 has a dynamic range n times larger than that of the primary filter 5 shown in FIG. FIG. 6 shows an example of the structure of a primary filter that can operate at a power supply voltage lower than that of the 20th embodiment. The primary filter 24 shown in FIG. 6 includes a first differential pair composed of a transistor Q1 as a first transistor and a diode-connected transistor Q2 as a first diode,
The transistor Q2n as the second transistor and the second
And a second differential pair constituted by a diode-connected Q2n-1 as a diode of the above. Also the primary filter 2
Reference numeral 4 denotes a diode-connected transistor Q in which first and second differential pairs are symmetrically arranged with a capacitor C for extracting a signal component in a predetermined band from both ends as a center.
2 and Q2n-1 and the capacitor C are connected in series.

Further, the primary filter 24 has a constant current source 25 having a first end connected to the ground line GND and a constant current source 25 having a first end connected to the power supply voltage V _CC and a diode serving as a second current source. Dedicated constant current source 26, constant current source 27 as a third current source whose one end is connected to ground line GND, and diode-dedicated constant current as a fourth current source whose one end is connected to power supply voltage V _CC It has a source 28 and 2n-4 diode-connected transistors Q3 ... Q2n-2 as a third diode.

Diode-connected transistor Q2
It is connected to the constant current source 25 and the diode only the constant current source 26 supplies a constant current 2I _F. As a result, the constant current I _F is supplied to the transistor Q2 through a path different from that of the transistor Q1, and the transistor Q2 is always kept in the conductive state.
The transistor Q2n-1, which is diode-connected is connected to the constant current source 27 and the diode only the constant current source 28 supplies a constant current 2I _F. As a result, the constant current I _F is supplied to the transistor Q2n-1 through a path different from that of the transistor Q2n, so that the transistor Q2n-1 is always kept in the conductive state.

The diode-connected 2n-4 transistors Q3 ... Q2n-2 are connected in series between the diode-connected transistors Q2 and Q2n-1, and their anodes or cathodes are connected next to each other. Has been done. Also, a diode-connected transistor Q
3 ... Q2n-2 has a constant current 2I _F connected to the constant current sources 26 and 28 and one end thereof connected to the power supply voltage V _CC or the ground line GND.
Alternatively, a diode constant current source 29 to 34 for supplying I _F
Connected to. Thus, the transistor Q3 ...... Q2n-2, which is diode-connected, each constant current I _F
Is supplied through a path separate from the first and second differential pairs, and is always kept in a conductive state.
For example, Q2 and Q3 operate differentially.

As a result, the primary filter 24 is equivalent to a state in which n emitter resistors re are connected in series between the bases of the transistors Q1 and Q2n forming the differential pair and the electrodes of the capacitor C. I can say. That is, it can be said that it is equivalent to the primary filter 20 shown in FIG. 5, and the dynamic range is n times larger than that of the primary filter 5 shown in FIG.

Therefore, the transfer function H of the primary filter 24 is
Is obtained by the equation (17), and it can be seen that it becomes a first-order low-pass filter. However, in the primary filter 24, the magnitude of the current flowing through the transistors Q1 to Q2n is I.
_Since it is _F , the value of the emitter resistance re is V _T / I.
It becomes _F. Further, the cutoff frequency fc of the primary filter 24 is calculated from the following equation (17).

[Equation 19] become that way.

Here, the lowest power supply voltage V _{CC at} which the primary filter 24 can operate is determined. If the voltage across the base emitters of the respective transistors Q1 to Q2n is V _BE, and the minimum operating voltage for operating the constant current source is V _I1 and V _I2 , the power supply voltage V required for the primary filter 24 to operate.
The condition of _CC is

(Equation 20) It is to satisfy. On the other hand, the condition of the power supply voltage V _CC required for the operation of the primary filter 20 shown in FIG.

(Equation 21) Was satisfied. As a result, the primary filter 24
Can operate at a power supply voltage lower than the primary filter 20 by (n-1) V _BE .

According to the above configuration, the capacitor C for extracting the signal component of the predetermined band from both ends is the transistor Q2 which is always connected by the diode-connected constant current source 26 of the first differential pair which is diode-connected. And a diode-connected constant current source 2 dedicated to the diode of the second differential pair
8 is connected in series with a transistor Q2n-1 which is always conducting by 8 and is always conducting by diode-connected constant current sources 26, 28, 29 to 34 (2n-4). By connecting the transistors Q3 ... Q2n-1 in series with the transistors Q2 and Q2n-1, it is possible to realize a primary filter having a much lower minimum operating voltage and a wider dynamic range. Further, similarly to the above-mentioned primary filter 20, the primary filter 24 does not need to be provided with the conventional common mode feedback circuit 4, so that the circuit configuration can be further downsized and the number of elements can be reduced. It can be much less.

(2-3) Low Power Consumption Primary Filter Next, using FIG. 7, the primary filter 2 shown in FIG.
The configuration of the primary filter 36 capable of reducing the power consumption as compared with the No. 4 will be described. This primary filter 36 and 1
The difference from the next filter 24 is that a diode-connected transistor Q2 serving as a fourth diode is provided between the first differential pair and a constant current source 37 serving as a first current source.
Q _N , Q _{N + 2} ... A plurality of Q _{N + Ms} are connected in series, and a second differential pair and a constant current source 3 as a third current source are provided.
A diode-connected transistor Q _{2Z-N + 1 ・ ・ ・} Q _2Z , Q _{2Z-N-M + 1 ・ ・ ・} Q as a fourth diode between
_This means that multiple _2Z-N-1s are connected in series.

In the primary filter 36, fourth and third diodes are arranged symmetrically with a capacitor C for extracting a signal component in a predetermined band from both ends as a center. That is, there are N−1 first emitters of the transistor Q 1 as the first transistor of the first differential pair and N−1 first emitters of the transistor Q _2Z-N as the second transistor of the second differential pair. 4 diodes are connected. In addition, M−1 fourth diodes are connected between the emitters of the diode-connected transistors Q _{N + 1} and Q _2Z-NM as the first and second diodes and the constant current sources 37 and 38, respectively. Has been done.

Similarly, hereafter, diode-connected transistors Q _ZKJ and Q _{Z + K + 1} as the third diode are provided.
, And J-1 third diodes are connected between the diode and the diode-dedicated constant current sources 39 and 40, respectively. Further, K− is provided between the emitters of the diode-connected transistors Q _Z and Q _{Z + 1} as the third diode and the diode-dedicated constant current sources 39 and 40, respectively.
One third diode is connected. Incidentally, the number of each diode can be set freely.

Here, the third filter used in the primary filter 24 is used.
The same number of third and fourth diodes as the first
And the case of connecting between the transistors Q1 and _{Q2Z-N of} the second differential pair. In this case, a plurality of diode-dedicated constant current sources 42 to 45 on the side of the power supply voltage V _CC and the ground line G
It is possible to reduce the plurality of diode-dedicated constant current sources 39 and 40 on the ND side according to the number N-1, M-1, ... Of a set of diodes. The fact that the number of diode-dedicated constant current sources 39, 40, 42 to 45 can be reduced in this way means that the power consumption can be further reduced. Incidentally, the values of the transfer function H and the cutoff frequency fc of the primary filter 36 are the same when the number of transistors is 2n.

According to the above configuration, it is possible to realize a primary filter which consumes less power than the circuit of FIG. In the case of this embodiment as well, similar effects can be obtained with respect to downsizing of the circuit, etc., as described in the above embodiments.

(3) Example of Applied Device Finally, an example of an electronic device using the above-mentioned primary filters 24 and 36 or the secondary filter constituted thereby will be described. FIG. 8 shows the reproducing system of the hard disk device 48 as a whole. In the magnetic disk device 48, the frequency of the signal read from the inner circumference side of the hard disk 49 and the frequency of the signal read from the outer circumference side are different,
The cut-off frequency fc is switched so as to correspond to each frequency. In this way, the above-mentioned filter is used for the filter portion for switching the cutoff frequency fc. Incidentally, even if the secondary filters are constructed by using the primary filters 24 and 36, the integrator is not required, so that the circuit configuration can be further simplified.

The hard disk device 48 amplifies the reproduction signal reproduced from the hard disk 49 via the magnetic head 50 in the recording / reproducing amplifier 51 and outputs it to the gain control amplifier 52. The gain control amplifier 52 amplifies the output signal so that the signal level becomes constant and outputs the amplified signal to the filter 53.

When the filter 53 extracts a signal component in a predetermined band, it outputs it to the peak detection circuit 54 and the gain control circuit 55. Gain control circuit 5
Reference numeral 5 determines the amplification degree of the gain control amplifier 52 based on the signal level of the extracted signal component, and outputs this to the gain control amplifier 52.

On the other hand, the peak detection circuit 54 peak-detects the extracted signal component and outputs it to the data separator 56. The data separator 56 separates data based on the peak-detected signal, and supplies the data to the decoder circuit 57. The decoder circuit 57 outputs the input signal to the NRZ
(Non return to zero) Convert to coded data and output. Through this series of operations, the hard disk device 48 is reproducing data.

According to the above construction, by using the primary filters 24 and 36 or the secondary filter for the filter 53, it is possible to obtain the hard disk device which can further reduce the mounting area. It is also possible to realize a low power supply voltage drive type hard disk device and a low power consumption type hard disk device.

(4) Other Embodiments In the above embodiment, the case where the secondary filter is composed of the primary filters 24 and 36 has been described, but the present invention is not limited to this, and other circuit configurations are possible. It can also be applied in some cases. In any case, since the secondary filter can be configured by the primary filter, the circuit scale can be reduced. In the above embodiment, the primary filter and the secondary filter
Although the following filter is described, the present invention is not limited to this.
It can also be applied to filters of third or higher order.

Further, in the above-described embodiment, the case where the differential pair and the diode are symmetrically arranged with the capacitor C as the center has been described, but the present invention is not limited to this, and the capacitor C may be the first differential pair. It can also be applied to the case of connecting in series at an arbitrary position between the emitter of the first transistor and the emitter of the second transistor of the second differential pair.
However, in this case as well, the first, second, third, and fourth diodes are always conducted by the diode-dedicated constant current source regardless of the connection position of the capacitor C.

Further, in the above-mentioned embodiment, the hard disk device has been described as an example of the device to which the filter of the embodiment is applied, but the present invention is not limited to this, and can be widely used for all electronic devices requiring the filter. it can.

[0056]

As described above, according to the present invention, a capacitor for extracting a signal component in a predetermined band from both ends is a diode dedicated to the first differential pair to which one input signal of the differential input signals is applied. The first diode which is always conducted by the second current source and the fourth diode which is dedicated to the diode of the second differential pair to which the other input signal is applied are always conducted. By connecting in series with the second diode, the circuit scale can be reduced, and the minimum operating voltage is much lower than the conventional one, and a filter circuit having a wider dynamic range and an electronic device using the same are realized. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic configuration of a filter circuit according to the present invention.

FIG. 2 is a block diagram showing a secondary filter constituted by a basic circuit of a filter circuit according to the present invention.

FIG. 3 is a circuit diagram showing a specific example of the block diagram shown in FIG.

FIG. 4 is a circuit diagram showing a specific example of the block diagram shown in FIG.

FIG. 5 is a circuit diagram showing a basic configuration of a filter circuit according to the present invention.

FIG. 6 is a circuit diagram showing an embodiment of a filter circuit according to the present invention.

FIG. 7 is a circuit diagram showing an embodiment of a filter circuit according to the present invention.

FIG. 8 is a circuit diagram showing an embodiment of an electronic device according to the present invention.

FIG. 9 is a block diagram showing a conventional primary low-pass filter.

FIG. 10 is a circuit diagram showing a configuration of a differential integrator.

[Explanation of symbols]

1 ... Differential integrator, 4 ... Common mode feedback circuit, 5, 20, 24, 36 ... Primary filter, 2,
3, 6, 7, 9-18, 21, 22, 25-34, 37
~ 46 …… constant current source, 8 …… secondary filter, 48 …… hard disk device, 49 …… hard disk, 50 ……
Magnetic head, 51 ... Recording / reproducing amplifier, 52 ... Gain control amplifier, 53 ... Filter, 54 ... Peak detection circuit, 55 ... Gain control circuit, 56
...... Data separator, 57 …… Decoder circuit.

Claims (6)

[Claims] 1. A first transistor having an input terminal to which one input signal of a differential input signal is applied, and a first transistor connected in series with an emitter of the first transistor to differentially operate with the first transistor. A first differential pair formed of a first diode, a first current source interposed between the emitter of the first transistor and the first power supply, and driving at least the first transistor; A second current source that is interposed between the first diode and the second power source and that always conducts the first diode; and a second input signal to which the other input signal of the differential input signals is applied to an input terminal. A second differential pair including a second transistor and a second diode connected in series with the emitter of the second transistor and differentially operating with the second transistor; and an emitter of the second transistor. A third current source that is interposed between the second diode and the first power source to drive at least the second transistor; and the third current source that is interposed between the second diode and the second power source. A fourth current source that always conducts the second diode and a first current source connected in series between the respective emitters of the first and second transistors,
A filter circuit comprising a capacitor for extracting a signal component in a predetermined band from both ends. 2. The filter circuit according to claim 1, wherein a third diode is connected in series between the first diode and the second diode. 3. The filter circuit according to claim 2, wherein the plurality of third diodes are arranged symmetrically with respect to the capacitor. 4. A fourth diode is connected in series between the emitter of the first transistor and the first diode and between the emitter of the second transistor and the second diode. Claim 1 characterized by the above.
The filter circuit described in. 5. An electronic device having a processing circuit for processing a signal based on a signal component of a predetermined band extracted by a filter circuit to which a differential input signal is applied, wherein the filter circuit has a differential input signal A first differential pair including a first transistor to which one input signal is applied and a first diode connected in series with the emitter of the first transistor and differentially operating with the first transistor. A first current source interposed between the emitter of the first transistor and the first power source to drive at least the first transistor, and between the first diode and the second power source. A second current source that is interposed between the first diode and the first diode to keep the first diode always conductive; a second transistor to which the other input signal of the differential input signals is applied to the input terminal; A second differential pair, which is connected in series with the emitter of the transistor and includes a second diode that operates differentially with the second transistor; and between the emitter of the second transistor and the first power supply. A third current source that is interposed between the second current source and the third current source that drives at least the second transistor, and that is always connected to the second diode; Between the current source and the respective emitters of the first and second transistors, and is connected in series with the first and second diodes,
An electronic device comprising a capacitor for extracting a signal component in a predetermined band from both ends. 6. The electronic device according to claim 5, further comprising a reproducing head for reproducing information from a recording medium, and a decoder for converting the extracted signal component of a predetermined band to reproduce data. machine.