JPS60136409A - Non-adjusting ic filter circuit - Google Patents

Abstract

PURPOSE:To obtain an IC filter circuit requiring no manual adjustments by correcting an RC active filter in an IC in accordance with the time constant of external elements so that this filter has a prescribed characteristic. CONSTITUTION:An oscillator OSC2 is oscillated with a frequency omega2 determined by values of external resistance Re and a capacitor Ce, and meanwhile, an oscillator OSC1 is oscillated with a frequency omega1 determined by values of internal resistance Ri0 and capacitor Ci0. Both frequency signals are inputted to a phase comparator PD, and the oscillator OSC1 is controlled through an LPF so that the frequency omega1 is equal to the frequency omega2. Time constants of RC active filters F1, F2...Fn are corrected by the same current as an output I of the LPF at this time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to circuit technology for forming an RC7C7 tape filter etc. with a specific frequency specification using integrated circuit technology, and particularly relates to the time constant of the RC7 tape filter. The present invention relates to a non-adjustable IC filter circuit that has a circuit function that can automatically adjust VC to a predetermined value.

[Background technology and its problems]

When forming a KRC7 vertical filter circuit on a single IC board, if the resistors and capacitors that determine the characteristics of the filter are formed on the board using IC technology, the absolute value accuracy will be very poor, and usually As it is, we cannot obtain anything usable, so we use an integrating circuit with a multiplier to create a biwatt type R.
There is a method of adjusting the Re active filter to predetermined characteristics by configuring the e active filter and adjusting only the external resistance value.

The feature of this method is that the resistance value is formed inside the IC.

Alternatively, the relative error in the capacitance value is originally small, so each integrating circuit is configured so that logarithmic parallel movement on the frequency axis can be performed using a multiplier, and the specific filter characteristics are By matching the points using the coefficients of the multiplier, it is possible to match the filter characteristics of all other filters at the same time.

However, in this adjustment method, it is necessary to supply No. 46 for each IC circuit board and check the characteristics while adjusting, so the adjustment work is still complicated.

[Purpose of the invention]

This invention was made to solve the above problems.
y, - accurate resistor and capacitor wire 7
Vc by attaching two externally to the IC circuit board? The present invention provides a non-adjustable IC filter circuit which allows A adjustment and easily obtains filter characteristics equivalent to the precision of externally attached resistors and capacitors without the need for V4 adjustment.

[A essential point of the invention]

This invention relates to a part of the substrate of an IC filter circuit formed of a combination of RC active filters whose time constants are commonly variable by a multiplier, etc.
Resistance formed by technology.

and a first oscillation circuit having a capacitor as a time constant; a second oscillation circuit having a specific number of externally attached high-precision resistors and capacitors; A PLL circuit is formed to match the oscillation frequency of the second oscillation circuit, and this PLL circuit
5 so that the multiplication coefficient of the multiplier is controlled by the difference signal current of the circuit.

Therefore, the characteristics of the filter formed by the IC circuit can be modified without adjustment in conjunction with the time constant of the externally attached resistor and capacitor having accurate values.

〔Example〕

FIG. 1 shows a non-all shaping IC filter circuit 9 of the present invention, the filter characteristics of which can be adjusted by control signals.

A first oscillation circuit oSC1 (217') is installed on a part of the substrate P as a circuit element for forming a control signal for automatically controlling a time constant, which is the object of the present invention.
m-times MOS C, a phase comparison ip D, and a loop filter LPF are formed.

1st, 11.2 (n oscillation circuit 0SC+, O8C
*k'! They have the same circuit configuration, for example, the second
As shown in the figure, it is a current-controlled CR oscillator whose oscillation period is determined by the Vcjll flows I and Io.

This current control type CR oscillator is a flip
A current source St + alternately driven by the output of F
S! + This (71 current source S1a St "KN" is a capacitor C that is charged and discharged according to the value I, and a terminal voltage of the capacitor C that is detected by the potential difference between both ends of the resistor R.
It consists of a voltage comparator DIID*Vc.

The operation of this oscillator is as follows.

When the capacitor C is charged by the current source sl and its terminal voltage becomes vI, the flip-flop F/F is inverted by the output from the voltage comparator D1, and the current source S is driven by its Q output. Therefore, capacitor C is current source S
, the current IK discharges n its terminal voltage decreases,
This voltage is ■.

When the voltage decreases to 1, the flip-flop F/F is reset by the output from the voltage comparator D2. Therefore, the current source S is driven again and the capacitor C is charged by the current IK. Thereafter, the current sources St and Ss are driven alternately to output an oscillation frequency -f with a period T.

In this CR oscillator, the comparison voltages are V and -V.

Since the value of is given by the current I0K of the current source S flowing through the resistor R, it can be understood from the oscillation waveform diagram in Figure 3. It constitutes a CR oscillator.

That is, the supplied current I, 1. The oscillation frequency is variable from VC and is proportional to the current IK.

Now, the first . Terminal T+ of second oscillation circuit 0SC1, O8C*
, T*K respectively as shown in FIG.
When the oscillation circuit 0SCzK is connected to an external resistor R0 and capacitors C and Y, each oscillation time constant ω8. ω
2 becomes.

G, -B”e, 1st and 2nd oscillation circuits O5C, OS
The relational expression ``Because C2'' is obtained.

This formula is expressed as: r+resistance (RIG)1 formed inside the IC board
It shows that the coefficients are the time constant of the capacitor (Cto) and the external resistance 11.

Once the resistance value is formed in the IC board.

Even if the capacitance value of the external resistor (Ro) and capacitor (C6
) is set to an accurate value, the time constant will be automatically corrected from the difference current (I = KI0) K obtained from the PLL circuit configuration.

RC7 filter FltF formed on the board
2...RC active filter Fl, F2 with relative error of time constant (R, m+ CI+) of Fn
......The time constant of FIl can also be corrected at the same time.

For example, FIG. 4 shows a biquadratic bandpass filter 10y! using an integral circuit with a multiplier. The first integrator 12A is composed of a differential amplifier 7'13A, a charging/discharging capacitor CA, and a multiplier 18AK, and the second integrator 12B is similarly constructed. Differential amplifier 13B
, a capacitor CB+a multiplier 18BK.

And, both species separators 12A and 12B have amplifiers 14°15,
and an adder 111 having an input terminal, r is connected in a ring through an adder 111, and a part of the output obtained at the output terminal 11 is connected to a resistor R, (R
b) -g is fed back to the second integrator 12Bk.

The transfer function (HB) is as follows.

Therefore, when the multiplication coefficient is 1, the central angular frequency ω is set by the time constant (RIIICIll) formed by the initial IC board. If the above-mentioned control current I=KI is supplied from the terminal 19, the accurate time constants (Ro, C, ) can be made into a bandpass filter having ω0 at a predetermined value of the central angular frequency adjusted by .

In this case, it is only necessary to assume that the relative error between the time constant (R, ., C+0) of the first oscillation circuit 0 S C+ and the time constant of the integrator (12A, 12B) is small. Therefore, even if a plurality of various filters formed by the integrator circuit of the multiplier are formed on the same substrate, all the filters 1. Second oscillation circuit O
S Or , 08 Cx is not limited to the circuit shown, in short, two electric currents 15! It goes without saying that any other type of oscillation circuit may be used as long as it is controlled by the ratio of (or voltage).

Also, RC active filter F+, Fa...
. . . The filter is not limited to the piwatt-type bandpass filter 16 illustrated in FIG. 4, but may be of any other circuit type as long as the time constant is controlled by a multiplication coefficient. .

〔Effect of the invention〕

The non-adjustable IC filter circuit of this invention operates in conjunction with the time constants of externally attached resistors and capacitors.

Multiple RC7 filters with multipliers formed in the IC circuit can be corrected to the desired characteristics without adjustment, so you can eliminate the IC filter circuit by simply externally connecting resistors and capacitors with accurate values. It has the advantage that it can be used with adjustments.

In addition, by using external resistors and capacitors with good accuracy and temperature characteristics, it is possible to obtain filter characteristics with much higher precision than with K.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an IC filter circuit showing an overview of the present invention, FIG. 2 is a circuit diagram showing an example of an oscillation circuit, and FIG.
The figure is a waveform diagram of an oscillation circuit, and FIG. 4 is a configuration diagram of a biquad type bandpass filter. In the figure, l+, Fa...F is an RC active filter, OS CI, 05 C! is the first. Second
oscillation circuit, PD is a phase comparator, LPF is a loop filter, and R6°C6 is an external resistor and capacitor.

Claims (1)

[Claims] A plurality of R whose time constants are commonly varied by a control signal.
Inside the IC board where the C7 filter is formed,
A resistor formed by an IC circuit. and a first oscillation circuit that uses a capacitor as a time constant; a second oscillation circuit that uses an external accurate resistor and a capacitor as a time constant; A non-adjustable IC characterized in that a PLL circuit is formed to match the oscillation frequencies of the second oscillation circuit, and the time constants of the plurality of RC7 filters are controlled by a difference signal of the PLL circuit. filter circuit.