JP2005192205A - Active filter circuit using gm amplifier, data read circuit, data write circuit and data reproducing device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active filter circuit using a gm amplifier, which reduces the number of circuit elements with excellent temperature characteristics in the active filter circuit. <P>SOLUTION: The present invention comprises an active filter having a first gm amplifier, a second gm amplifier equivalent to the first gm amplifier, a band gap power source which applies a constant voltage making use of a band gap voltage to an input of the second gm amplifier, and a current-voltage conversion circuit which converts an output current of the second gm amplifier into a voltage, wherein operation currents of the first and second gm amplifiers are controlled depending on the output voltage of the current-voltage conversion circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an active filter circuit using a gm amplifier (transconductance amplifier), a data read circuit using the same, a data write circuit, and a data reproduction device, and more particularly to a data signal extraction circuit for a CD, MD, DVD, etc. In a frequency band variable active filter circuit used for frequency band switching at the time of n-times reproduction or n-times speed writing with respect to a prescribed reproduction speed and a prescribed writing speed in a data demodulator circuit of a wobble signal or the like, a temperature characteristic is good The present invention relates to an improvement of an active filter circuit using a gm amplifier capable of reducing the number of circuit elements.

In recent CD-R / RW, the data writing speed has been increased by 2 times, 4 times, 8 times, and so on. In this CD-R / RW, normally, write data transferred from a host computer through an interface such as SCSI or ATPI is EFM-modulated and added to the laser controller. The laser light controlled for writing by the laser controller is turned on / off by the EFM-modulated data and applied to a predetermined track of the CD, whereby data writing is performed on the predetermined track.
In addition to such a CD-R / RW, in an optical disk such as a CD-R or DVD-RAM, by forming a meandering groove (groove), synchronization information and address information ( Absolute time information) is recorded as a wobble signal.

The wobble signal is a signal that has been FSK modulated with the biphase code modulation signal BIDATA, and the wobble frequency fWBL is 22.05 ± 1 kHz (during 1 × speed reproduction) when the disc rotation is at a specified linear velocity. An ATIP (absolute time in pregroove) signal including absolute time information reproduced from a wobble signal is composed of a synchronization signal, address data (absolute time data), and error detection code CRC as BIDATA. Usually, the unit is 42 bits. The repetition frequency of the synchronization signal is 75 Hz.
In order to reproduce such data recorded on the optical disc as a wobble signal, a demodulation circuit having an active filter circuit for demodulating the data of the wobble signal is required. An optical disk apparatus using this type of demodulation circuit is described in Japanese Patent Application Laid-Open No. 9-297969 or Japanese Patent Application Laid-Open No. 11-16291 (Patent Documents 1 and 2).
JP-A-9-297969 Japanese Patent Laid-Open No. 11-16291

In addition to such a wobble signal, a variable gm amplifier is used as an active filter circuit for extracting this type of data. FIG. 5 shows an example of the active filter circuit.
The active filter circuit 10 includes a gm / C filter circuit 11 and a frequency band setting signal generation circuit 12.
The gm / C filter circuit 11 is an integrating circuit including a gm amplifier 11a and a capacitor C, and normally constitutes a low-pass filter. In order to configure the band-pass filter, a differentiation circuit (high-pass filter (HPF)) including a gm amplifier 11a and a capacitor Ca is connected to the preceding stage or the subsequent stage. In the case of the differentiation circuit, the gm amplifier becomes substantially the same circuit only by inserting a capacitor on the input side of the gm amplifier.

In order to simplify the description, a low-pass filter (LPF) will be described below as an example.
The (+) input (positive phase input or non-inverting input) terminal (hereinafter referred to as (+) input) and the (−) input (reverse phase input or inverted input) terminal (hereinafter referred to as (−) input) of the gm amplifier 11a are, for example, A read signal such as a wobble signal is applied as a differential input from a signal source 20 such as a read amplifier. A capacitor C is connected to the output side of the gm amplifier 11a to form a low pass filter (LPF), and its output is obtained at the output terminal 11c. Reference numeral 11b denotes a current source (operating current source) for setting the operating current of the gm amplifier 11a.
The frequency band setting signal generation circuit 12 sets the cutoff frequency of the low-pass filter to a predetermined value by controlling the current value of the operating current source 11b. At the same time, the cut-off frequency of the high-pass filter (not shown) of the differentiating circuit composed of the gm amplifier 11a and the capacitor Ca is set to a predetermined value at the preceding stage or the subsequent stage to set the band of the band-pass filter. The gm amplifier 11a is an R (resistance) simulation circuit, and the resistance value of R to be simulated changes according to the current value of the operating current source 11b of the gm amplifier 11a. Thereby, the CR filter circuit is simulated.
Therefore, the frequency band setting signal generation circuit 12 selects the resistance value of the simulation resistor by setting the current value of the operating current source 11b to the selected constant value. Thereby, the cutoff frequency of the low-pass filter is determined in relation to the capacitance of the capacitor C (or / and the capacitor Ca).
The frequency band setting signal generation circuit 12 includes a first low-pass filter circuit 13, a first buffer amplifier (voltage follower) 14, a second low-pass filter circuit 15, a second buffer amplifier (voltage follower) 16, and a multiplication circuit. 17, a low-pass filter (LPF) 18, and a voltage-current (V-I) conversion circuit 19. The (−) input side of the amplifier of each circuit is connected to each other, and the output of the second buffer amplifier 16 is fed back to the (−) input side of the low-pass filter circuit 13 as a signal having an opposite phase.

The first low-pass filter circuit 13 includes a gm amplifier 13a equivalent to the gm amplifier 11a, a capacitor C1, and an operating current source 13b of the gm amplifier 13a. This is a circuit equivalent to the gm · C filter circuit 11. A reference clock CLK frequency-divided from an oscillation circuit or the like through a frequency divider circuit or the like (not shown) is received via the input terminal 12a on the (+) input side. The output of the low-pass filter circuit 13 is added to the (+) input of the first buffer amplifier 14. The output of the first buffer amplifier 14 is sent to the (+) input of the second low-pass filter circuit 15.
The second low-pass filter circuit 15 includes a gm amplifier 15a equivalent to the gm amplifier 11a, a capacitor C2, and an operating current source 15b of the gm amplifier 15a. This is also a circuit equivalent to the gm · C filter circuit 11. The output of the low-pass filter circuit 15 is sent to the (+) input of the second buffer amplifier 16. The output of the second buffer amplifier 16 is sent to the multiplication circuit 17.
The multiplier circuit 17 receives the clock CLK input via the input terminal 12a at the (−) input, passes through the first and second low-pass filter circuits 13 and 15, and the reference clock CLK shifted in phase by 180 ° and the original clock CLK. A phase comparison with the reference clock CLK is performed to generate a voltage output corresponding to the phase shift amount of the clock CLK. This is received by a low-pass filter (LPF) 18, where a voltage corresponding to the amount of deviation is obtained as an integrated value, and this integrated voltage is converted into a current value by the VI conversion circuit 19. In response to the converted current value, the frequency band setting signal generation circuit 12 controls the current values of the operating current sources 13b and 15b of the respective gm amplifiers, respectively, so that the reference clock CLK and the original reference clock are 180 degrees out of phase. Negative feedback control is performed in a direction in which a phase shift from CLK does not occur.
As a result, a control current value having a frequency corresponding to the reference clock CLK is generated in the frequency band setting signal generation circuit 12, and the operating current sources 11b, 13b, and 15b are controlled in the three gm amplifiers that are equivalent circuits. The cutoff frequency of the gm · C filter circuit 11 is set to a desired value. Therefore, the selection of the cutoff frequency of the gm · C filter circuit 11 is performed by selecting or switching the frequency of the reference clock CLK.

In the circuit as described above, the frequency band setting signal generation circuit 12 has two gm · C filter circuits equivalent to the gm · C filter circuit 11 and two buffer amplifiers in order to set the frequency with high accuracy. It is necessary to provide a multiplication circuit circuit attached thereto. This makes it possible to select a frequency band with good temperature characteristics and high accuracy. However, this requires a large number of elements constituting the circuit. In addition, there is a disadvantage that the occupied area becomes large when the active filter circuit is integrated into an IC because the pairing property of each element is required and the number of elements is large.
An object of the present invention is to solve such drawbacks of the prior art, and in an active filter circuit, there is provided an active filter circuit using a gm amplifier that has good temperature characteristics and can reduce the number of circuit elements. It is to provide.
Another object of the present invention is to provide a data read circuit, data write circuit, or data reproduction device having an active filter circuit using a gm amplifier, which has good temperature characteristics and can reduce the number of circuit elements. is there.

In order to achieve the above object, the active filter circuit of the first invention comprises an active filter having a first gm amplifier, a second gm amplifier equivalent to the first gm amplifier, and the second And a current-voltage conversion circuit for converting the output current of the second gm amplifier into a voltage, and an output of the current-voltage conversion circuit. The operating current of the first and second gm amplifiers is controlled according to the voltage.
The second invention further comprises a voltage-current conversion circuit for converting the output voltage of the current-voltage conversion circuit into a current, and the first and the second are selected according to the output current of the voltage-current conversion circuit. The operating current of the second gm amplifier is controlled.

As described above, according to the present invention, a current that does not depend on temperature is generated by the gm amplifier equivalent to the gm amplifier of the active filter circuit using the band gap power supply, and the generated current is generated by the active filter circuit. The voltage is converted by a current-voltage conversion circuit into a voltage value that generates an operating current corresponding to the cutoff frequency. The operating current of the gm amplifier of the active filter circuit is controlled according to the output voltage of the current-voltage conversion circuit.
As a result, a stable filter circuit with good temperature characteristics can be manufactured without receiving the reference clock CLK and without requiring a plurality of circuits such as a plurality of gm amplifiers, buffer amplifiers, and phase comparison circuits. Therefore, when this active filter circuit is made into an IC, the occupied area can be reduced. The cutoff frequency of the active filter circuit can be easily selected by selecting the conversion rate of the current-voltage conversion circuit. That is, the cut-off frequency can be selected by using, for example, a variable resistor or a variable constant voltage circuit externally attached to the IC as the current-voltage conversion circuit.
As a result, an active filter circuit using a gm amplifier that has good temperature characteristics and can reduce the number of circuit elements can be easily realized. The data read circuit, data write circuit, and data reproduction device having this active filter circuit are also circuits or devices that can enjoy the same operation.

FIG. 1 is a block diagram of an embodiment to which an active filter circuit using a gm amplifier of the present invention is applied, FIG. 2 is a block diagram of another embodiment, and FIG. 3 is a block diagram of still another embodiment. FIG. 4 and FIG. 4 are block diagrams of still another embodiment.
In each figure, the same component is denoted by the same reference numeral, and the description of the configuration is omitted.

In FIG. 1, reference numeral 1 denotes an active filter circuit comprising a gm · C filter circuit 11 and a frequency band setting signal generation circuit 2. In each figure, the same component is given the same reference numeral, and the description of the component is omitted.
The frequency band setting signal generation circuit 2 includes a band gap power source 3 (which can be a constant voltage circuit) that generates a constant voltage as a power source voltage using a band gap voltage having forward diode characteristics, a gm amplifier 13a, and a current-voltage conversion. The circuit 4 and a voltage-current (VI) conversion circuit 19 are included. The band gap power supply 3 is inserted between the (+) input terminal 13d and the (−) input terminal 13e of the gm amplifier 13a, and applies the reference voltage Vref to the (+) input terminal 13d and the (−) input terminal 13e. To do. The current-voltage conversion circuit 4 includes a resistor R and a constant voltage circuit 5, and the resistor R is connected between the output terminal 13c of the gm amplifier 13a and the ground GND. This circuit converts the output current of the gm amplifier 13a into a voltage. The constant voltage circuit 5 generates a constant voltage Vin and is connected to the ground GND and the (−) input terminal 19 b of the voltage-current (VI) conversion circuit 19.
The output terminal 13 c of the gm amplifier 13 a is connected to the (+) input terminal 19 a of the voltage-current (VI) conversion circuit 19. Here, the capacitor C1 in FIG. 5 is omitted. Therefore, the voltage applied between the (+) input terminal 19a and the (−) input terminal 19b of the voltage-current (VI) conversion circuit 19 is obtained by subtracting the constant voltage Vin from the terminal voltage Vout of the resistor R. It becomes a voltage value.

Here, the output current of the gm amplifier 13a is obtained by converting the reference voltage Vref of the bandgap power supply 3 into a current value, and since this voltage is a constant voltage using the bandgap voltage, the output current substantially reaches the temperature. The voltage is unaffected. Therefore, the output current of the gm amplifier 13a is also a constant current that is not affected by temperature. As a result, the voltage Vout obtained by converting this current by the resistor R becomes a similar voltage.
Here, the current value of the control current of the cut-off frequency of the gm / C filter circuit 11 is i, and the input voltage value (conversion voltage value) to be converted before the VI conversion for generating this current value i is Vs. .
Vs = Vout−Vin (1)
It becomes. Therefore, by selecting the terminal voltage Vout of the resistor R of the current-voltage conversion circuit 4 and the constant voltage Vin of the constant voltage circuit 5, the gm · C filter circuit 11 has a predetermined cut-off frequency to be obtained and is not influenced by temperature. It becomes a filter circuit. In other words, in this embodiment, the resistance value of the resistor R of the current-voltage conversion circuit 4 and the constant voltage value Vin of the constant voltage circuit 5 are selected corresponding to the cutoff frequency of the gm · C filter circuit 11.
The gm of the gm amplifier 13a is
gm = 1 / R · Vin / Vref (2)
It can be expressed as Here, R is the resistance value of the resistor R.

In FIG. 1, if the resistor R is a variable resistor, the current value i of the control current can be adjusted and selected. Thereby, the cutoff frequency of the gm · C filter circuit 11 can be selected.
In the drawing, a differentiation circuit composed of a gm · C filter circuit 11 and a capacitor Ca indicated by a dotted line constitutes a high-pass filter 21. As shown in the figure, the high-pass filter 21 can be cascade-connected to the active filter circuit 10 to form a band-pass filter. By controlling the current source 11b of the high-pass filter 21 simultaneously with the current source 11b of the active filter circuit 10, the band of the band-pass filter can be set to a predetermined value. Further, as will be described later, the band of the band-pass filter can be selected by making the resistor R a variable resistor or making the voltage value Vin of the constant voltage circuit 5 variable. Such a bandpass filter is used as a data reading device or a data writing device.
FIG. 2 shows an embodiment in which the resistor R of FIG. 1 is an external resistor and a variable resistor. A description of the operation is omitted.
The feature of the active filter circuit of FIG. 2 is that the variation in circuit characteristics can be adjusted by the variable resistor by providing the resistor R as an external resistor and a variable resistor. Thereby, the dispersion | variation in the filter characteristic for every product can be absorbed. Of course, the external resistor R may not be a variable resistor, but simply an external resistor, and the resistance value may be selected for each to adjust the variation. Alternatively, the cutoff frequency of the gm · C filter circuit 11 may be selected according to the resistance value of the external resistor R.

In FIG. 3, instead of the variable resistor R of FIG. 2, an external fixed resistor is simply used, the voltage value Vin on the constant voltage circuit 5 side is made variable, and this is replaced with a variable constant voltage generating circuit 6.
In this embodiment, the bandgap power supply 3 of FIG. 1 includes a bandgap power supply voltage generation circuit 30 and a voltage dividing resistor circuit 31 as a bandgap power supply circuit. A reference voltage Vref is generated at the terminal voltage of the resistor R1 with the connection point N1 of the resistors R1 and R2 of the voltage dividing resistor circuit 31 as a reference point.
The gm amplifier 13a is a variable Gm amplifier composed of differential amplifiers 130 and 131 connected in two stages. The differential inputs of the differential amplifiers 130 and 131 receive the reference voltage Vref. The differential amplifiers 130 and 131 have current mirror circuits 132 and 133 having a common active load. The current mirror circuits 132 and 133 are stacked in two stages on the power supply line side and are cascade-connected. The emitter area ratios (or the number of connected cells) of the differential transistors of the differential amplifiers 130 and 131 are 1: 4 and 4: 1, respectively.
The gm amplifier 11a of the gm · C filter circuit 11 shown on the right side of the drawing is a similar circuit.
The output of the differential amplifier 130 is taken out from the connection point N2 between the output side transistor of the current mirror circuit 132 and one of the differential transistors, and is supplied to the (+) input terminal 19a of the voltage-current (VI) conversion circuit 19. Added.

The variable constant voltage generation circuit 6 for generating the variable voltage value Vin includes a ladder-type D / A conversion circuit (R-2R / DAC) 6a and a register 6b, and data is set in the register 6b from the MPU or the like. The R-2R / DAC 6a D / A converts the data to generate a voltage value Vin according to the set data. These constitute a programmable constant voltage generation circuit.
As the voltage value Vin in this case, data for setting the cutoff frequency of the gm · C filter circuit 11 is given to the register 6b. As a result, the cutoff frequency of the gm · C filter circuit 11 is selected. That is, the gm · C filter circuit 11 is a variable filter.
By the way, the resistance R1 of the voltage dividing resistor circuit 31 that generates the reference voltage Vref and the R-2R resistors constituting the ladder-type D / A converter circuit 6a are set to the same resistance value, and an IC is formed using highly paired resistors. By doing so, it is possible to reduce variations in the characteristics of the filter circuits.
The resistor R is a fixed resistor, but it goes without saying that it may be a variable resistor shown in FIG. Further, if the variable constant voltage generating circuit 6 is provided in series on the variable resistor R side, the variable constant voltage generating circuit 6 can be used as the voltage generating circuit 5 without being the variable constant voltage generating circuit 6. That is, the circuit for generating the input voltage value Vs may be constituted by the variable resistor R and a constant voltage generating circuit for applying a constant voltage to the terminal of the variable resistor R.

FIG. 4 shows an embodiment in the case of extracting a wobble signal or the like read from an optical disc (CD, DVD, etc.), and filters according to a multiple (2 times, 4 times, 8 times,...) Of the data writing speed. Is a data write circuit or a data read circuit that selects a cutoff frequency of 3T to 11T. Note that the cascade-connected high-pass filter 21 is omitted in the figure.
A part of the signal output to the output terminal 11c of the gm / C filter circuit 11 in FIG. 3 is input to a DSP (digital signal processor) 7, and a pulse signal P corresponding to a multiple of the writing speed is generated. This pulse signal P is input to the PWM pulse generation circuit 8 to generate a PWM pulse Ppwm corresponding to a multiple of the writing speed, and this is input to the T-type LPF 9 to integrate and divide the data to write the data. A voltage value Vin corresponding to a multiple of is generated.
Thus, a voltage value Vin corresponding to a multiple (2 times, 4 times, 8 times,...) Of the data write speed is obtained, and the cutoff frequency of the gm / C filter circuit 11 is set to a multiple (2 times, (4 times, 8 times,...) Can be set. At this time, the cutoff frequency of the high-pass filter 21 (not shown) is set at the same time.

As described above, in the embodiment, the conversion voltage Vs is subtracted from the terminal voltage of the resistor R as Vs = Vout−Vin. However, this may be added as Vs = Vout + Vin. Of course it is good. One example is the case where a voltage generating circuit is provided in series on the variable resistor R side as described above. Note that this is possible even if the voltage of the constant voltage Vin of the constant voltage circuit 5 in FIG.
In the embodiment, the voltage value of the current-voltage conversion circuit 4 is converted by the voltage-current (V-I) conversion circuit 19 to obtain the control current value. However, the current-voltage conversion is performed via a buffer amplifier or the like. It is possible to control the operating current of the gm amplifier according to the voltage value of the circuit 4.
Furthermore, the frequency band setting signal generation circuit 2 of the embodiment controls to set the cutoff frequency of the LPF (low pass filter). Further, as shown by a dotted line in FIG. 1, an HPF (high pass filter) is cascade connected to the subsequent stage or the preceding stage, and the operating current source of the gm amplifier of this HPF is voltage-current (V-I). Of course, the entire configuration can be configured as a band-pass filter by controlling simultaneously with the output current of the conversion circuit 19.
The gm amplifiers in the embodiments of FIGS. 3 and 4 are examples, and it is needless to say that various gm amplifier circuits can be used.

FIG. 1 is a block diagram of an embodiment to which an active filter circuit using a gm amplifier according to the present invention is applied. FIG. 2 is a block diagram of another embodiment. FIG. 3 is a block diagram of still another embodiment. FIG. 4 is a block diagram of still another embodiment. FIG. 5 is an explanatory diagram of an example of a conventional active filter circuit.

Explanation of symbols

1, 10 ... Active filter circuit,
2, 12 ... frequency band setting signal generation circuit,
3 ... Bandgap power supply,
4 ... current-voltage conversion circuit, 5 ... constant voltage circuit,
6 ... variable constant voltage generation circuit, 7 ... DSP (digital signal processor),
8 ... PWM pulse generation circuit, 9 ... T-type LPF,
11 ... gm · C filter circuit,
11a, 13a ... gm amplifier, 11b, 13b, 15b ... operating current source,
11c: Output terminal,
13, 15, 18 ... low-pass filter circuit,
14, 16 ... Buffer amplifier (voltage follower),
17 ... multiplication circuit, 19 ... voltage-current (VI) conversion circuit,
30 ... Band gap power supply voltage generation circuit, 31 ... Voltage divider resistor circuit,
R, R1, R2 ... resistor, C ... capacitor.

Claims (20)

  An active filter having a first gm amplifier, a second gm amplifier equivalent to the first gm amplifier, and a bandgap power source for applying a constant voltage using a bandgap voltage to the input of the second gm amplifier; And a current-voltage conversion circuit that converts the output current of the second gm amplifier into a voltage, and controls the operating current of the first and second gm amplifiers according to the output voltage of the current-voltage conversion circuit Active filter circuit using gm amplifier.   And a voltage-current conversion circuit that converts the output voltage of the current-voltage conversion circuit into a current. The operating currents of the first and second gm amplifiers are converted into the output current of the voltage-current conversion circuit. 2. An active filter circuit using the gm amplifier according to claim 1, which is controlled accordingly.   An active filter having a first gm amplifier having a (+) input and a (−) input; a second gm amplifier equivalent to the first gm amplifier; and a (+) input of the second gm amplifier; (-) A band gap power supply circuit that applies a constant voltage using a band gap voltage to the input, a current-voltage conversion circuit that converts the output current of the second gm amplifier into a voltage, and the current-voltage conversion A voltage-current conversion circuit for converting a voltage output of the circuit into a current, and an operation current of the first and second gm amplifiers is set according to an output current of the voltage-current conversion circuit. Had active filter circuit.   The current-voltage conversion circuit has a resistor that generates a predetermined voltage in response to an output current of the second gm amplifier, and a conversion voltage corresponding to an operating current in which the active filter becomes a filter having a predetermined cutoff frequency. The active filter circuit using the gm amplifier according to claim 3, wherein: is generated according to a terminal voltage of the resistor.   The band gap power supply is a constant voltage circuit that generates a constant voltage using a band gap voltage having a forward diode characteristic, and the first gm amplifier includes a plurality of first gm amplifiers. And an integration circuit is constituted by one of the first gm amplifiers and a first capacitor among a plurality, and another one of the first gm amplifiers and a second capacitor among the plurality of the first gm amplifiers. A differential circuit, and the active filter is configured by the cascade connection of the integration circuit and the differentiation circuit, and the voltage-current conversion circuit has a (+) input and a (−) input, The current-voltage conversion circuit further includes a constant voltage circuit that generates a predetermined voltage to be added to or subtracted from the terminal voltage, and the current-voltage conversion circuit includes the (+) input and the (−) input of the voltage-current conversion circuit. Resistance terminal voltage Active filter circuit using a gm amplifier according to claim 4 wherein the output current conversion circuit - the voltage a voltage obtained by adding or subtracting the predetermined voltage, as the conversion voltage with respect.   6. The active filter circuit using a gm amplifier according to claim 5, wherein the resistor is a variable resistor, and a resistance value of the variable resistor is selected so as to be the predetermined cutoff frequency.   6. The active filter circuit using a gm amplifier according to claim 5, wherein the constant voltage circuit is a programmable constant voltage generation circuit that receives data from outside the circuit and generates a constant voltage according to the data. In a data read circuit having an active filter having a first gm amplifier and a capacitor, and a setting signal generating circuit for setting a cutoff frequency of the active filter to a predetermined value by controlling an operating current of the first gm amplifier ,
The setting signal generation circuit includes a second gm amplifier equivalent to the first gm amplifier, a bandgap power source that applies a constant voltage using a bandgap voltage to an input of the second gm amplifier, and the second gm amplifier. A data read circuit for controlling an operating current of each of the first and second gm amplifiers according to an output voltage of the current-voltage conversion circuit; and a current-voltage conversion circuit for converting an output current of the amplifier into a voltage.   The setting signal generation circuit further includes a voltage-current conversion circuit that converts the output voltage of the current-voltage conversion circuit into a current, and an operating current of the first and second gm amplifiers is the voltage− 9. The data read circuit according to claim 8, wherein the data read circuit is controlled in accordance with an output current of the current conversion circuit. In a data read circuit having an active filter having a first gm amplifier and a capacitor, and a setting signal generating circuit for setting a cutoff frequency of the active filter to a predetermined value by controlling an operating current of the first gm amplifier ,
In the setting signal generation circuit, the first gm amplifier has a (+) input and a (−) input, a second gm amplifier equivalent to the first gm amplifier, and the second gm amplifier. A band gap power supply circuit that applies a constant voltage using a band gap voltage between the (+) input and the (−) input; a current-voltage conversion circuit that converts the output current of the second gm amplifier into a voltage; A voltage-current conversion circuit for converting the voltage output of the current-voltage conversion circuit into a current, and the operating currents of the first and second gm amplifiers are set according to the output current of the voltage-current conversion circuit. Data read circuit.   The current-voltage conversion circuit has a resistor that generates a predetermined voltage in response to an output current of the second gm amplifier, and a conversion voltage corresponding to an operating current in which the active filter becomes a filter having a predetermined cutoff frequency. The data read circuit according to claim 10, wherein the data is generated according to a terminal voltage of the resistor.   The voltage-current conversion circuit has a (+) input and a (-) input, and the current-voltage conversion circuit has a constant voltage circuit that generates a predetermined voltage to be added to or subtracted from the terminal voltage, 11. The data according to claim 10, wherein a voltage obtained by adding or subtracting the predetermined voltage to the terminal voltage of the resistor is output as the conversion voltage between a (+) input and a (−) input of the voltage-current conversion circuit. Read circuit.   The band gap power supply is a constant voltage circuit that generates a constant voltage using a band gap voltage having a forward diode characteristic, and the first gm amplifier includes a plurality of first gm amplifiers. And an integration circuit is constituted by one of the first gm amplifiers and a first capacitor among a plurality, and another one of the first gm amplifiers and a second capacitor among the plurality of the first gm amplifiers. A differential circuit, and the active filter is configured by the cascade connection of the integration circuit and the differentiation circuit, and the voltage-current conversion circuit has a (+) input and a (−) input, The current-voltage conversion circuit further includes a constant voltage circuit that generates a predetermined voltage to be added to or subtracted from the terminal voltage, and the current-voltage conversion circuit includes the (+) input and the (−) input of the voltage-current conversion circuit. Resistance terminal voltage Data read circuit according to claim 12 wherein the output current conversion circuit - a voltage obtained by adding or subtracting the predetermined voltage said voltage as the conversion voltage with respect. A data writing circuit having an active filter having a first gm amplifier and a capacitor, and a setting signal generating circuit for setting a cutoff frequency of the active filter to a predetermined value by controlling an operating current of the first gm amplifier In
The setting signal generation circuit includes a second gm amplifier equivalent to the first gm amplifier, a bandgap power source that applies a constant voltage using a bandgap voltage to an input of the second gm amplifier, and the second gm amplifier. A data write circuit for controlling an operating current of each of the first and second gm amplifiers according to an output voltage of the current-voltage conversion circuit, the current-voltage conversion circuit converting the output current of the amplifier into a voltage .   The setting signal generation circuit further includes a voltage-current conversion circuit that converts the output voltage of the current-voltage conversion circuit into a current, and an operating current of the first and second gm amplifiers is the voltage− 15. The data write circuit according to claim 14, wherein the data write circuit is controlled in accordance with an output current of the current conversion circuit. A data writing circuit having an active filter having a first gm amplifier and a capacitor, and a setting signal generating circuit for setting a cutoff frequency of the active filter to a predetermined value by controlling an operating current of the first gm amplifier In
In the setting signal generation circuit, the first gm amplifier has a (+) input and a (−) input, a second gm amplifier equivalent to the first gm amplifier, and the second gm amplifier. A band gap power supply circuit that applies a constant voltage using a band gap voltage between the (+) input and the (−) input; a current-voltage conversion circuit that converts the output current of the second gm amplifier into a voltage; A voltage-current conversion circuit for converting the voltage output of the current-voltage conversion circuit into a current, and the operating currents of the first and second gm amplifiers are set according to the output current of the voltage-current conversion circuit. Data writing circuit.   The current-voltage conversion circuit has a resistor that generates a predetermined voltage in response to an output current of the second gm amplifier, and a conversion voltage corresponding to an operating current in which the active filter becomes a filter having a predetermined cutoff frequency. The data write circuit according to claim 16, wherein the data is generated according to a terminal voltage of the resistor.   The voltage-current conversion circuit has a (+) input and a (-) input, and the current-voltage conversion circuit has a constant voltage circuit that generates a predetermined voltage to be added to or subtracted from the terminal voltage, The data according to claim 17, wherein a voltage obtained by adding or subtracting the predetermined voltage to or from the terminal voltage of the resistor is output as the conversion voltage between a (+) input and a (-) input of the voltage-current conversion circuit. Write circuit.   The band gap power supply is a constant voltage circuit that generates a constant voltage using a band gap voltage having a forward diode characteristic, and the first gm amplifier includes a plurality of first gm amplifiers. And an integration circuit is constituted by one of the first gm amplifiers and a first capacitor among a plurality, and another one of the first gm amplifiers and a second capacitor among the plurality of the first gm amplifiers. A differential circuit, and the active filter is configured by the cascade connection of the integration circuit and the differentiation circuit, and the voltage-current conversion circuit has a (+) input and a (−) input, The current-voltage conversion circuit further includes a constant voltage circuit that generates a predetermined voltage to be added to or subtracted from the terminal voltage, and the current-voltage conversion circuit includes the (+) input and the (−) input of the voltage-current conversion circuit. Resistance terminal voltage Data write circuit of claim 18 wherein the output current conversion circuit - a voltage obtained by adding or subtracting the predetermined voltage said voltage as the conversion voltage with respect. A data reproduction circuit comprising: an active filter having a first gm amplifier and a capacitor; and a setting signal generating circuit for setting a cutoff frequency of the active filter to a predetermined value by controlling an operating current of the first gm amplifier.
The setting signal generation circuit includes a second gm amplifier equivalent to the first gm amplifier, a bandgap power source that applies a constant voltage using a bandgap voltage to an input of the second gm amplifier, and the second gm amplifier. A data-reproducing circuit having a current-voltage converting circuit for converting an output current of the amplifier into a voltage, and controlling an operating current of the first and second gm amplifiers according to an output voltage of the current-voltage converting circuit.

Images