JPS60190015A - Integrated circuit - Google Patents

Abstract

PURPOSE:To obtain an integrated active BPF circuit having a desired characteristic by providing a limiter circuit to an output section of the active BPF composing a resistor, a capacitor and an amplifier so as to absorb the fluctuation of an output amplitude depending on variation in a time constant circuit. CONSTITUTION:The variation of the output amplitude of the BPF circuit attended with the changeover is suppressed by connecting the limiter circuit 16 to an output terminal of the active BPF with time constant switching circuits 12, 13. An input signal from an input terminal 21 is inputted to a base of Trs Q1, Q2 constituting a differential amplifier in the circuit 16 and only the DC component of input signal is propagated because of the capacitance 19. The difference of the input signal is multiplied by a factor of the gain at the differential amplifier and the signal is outputted from a terminal 15 while the upper and lower limit of the output signal is limited because this circuit has a high gain. Thus, even if the input signal amplitude is fluctuated, a limit is given over the output signal by increasing sufficiently the gain of the differential amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an integrated circuit on an IC, and particularly to an integrated filter suitable for a band pass filter (hereinafter abbreviated as BPF).

[Background of the invention]

Integration of electrical circuits (monolithic IC, hereinafter simply IC)
(abbreviated as "I") progresses, the I
C conversion leads to the miniaturization of circuit boards.

This is becoming an important issue in achieving cost reduction.

Most conventional filters have an inductance L and a capacitance C1.
Although it is composed of a resistor R, it is difficult to integrate an inductance into an IC, so it is difficult to integrate a conventional filter. For this reason, an active filter consisting of a capacitor C1 resistor and an amplifier has been implemented as an IC. An example of a block diagram of a feedback type active BPF is shown in FIG. 1 and will be described below. 1 is a signal input terminal, 4 is a signal output terminal, 2 is a gain and a feedback amplifier, 6 is a gain and a feedback amplifier of 2, a resistor and capacitors C1 to C4 are for time constants. Resistance 1 to 14. Capacitors CI and C3 and feedback amplifier 2 form a quadratic high-pass filter (hereinafter abbreviated as PF), and resistor 1 (Iζ), capacitors C8 and C2, and feedback amplifier 6 form a quadratic low-pass filter. Pass filters (hereinafter abbreviated as L P F) are respectively configured, and a BPF is configured by combining the HPF and L P F''.

However, when converting the BPF with the above configuration into an IC, a problem of variation occurs. That is, the capacitance value and resistance value within the IC are affected by variations due to impurity concentration within the semiconductor, mask misalignment, etc., and have large fluctuations, such as an absolute value of C of about ±20% and an absolute value of 115%. Therefore, the BPF in Figure 1
The peak frequency fp also varies in the range from a to b as shown in FIG. 2, and in the above example, the worst case frequency fp varies by ±35 degrees, making it extremely difficult to put it into practical use. As a countermeasure to this variation in element values, attempts have been made to change the resistance value on the IC chip by laser trimming, etc. to absorb the variation, but there are still many problems in terms of accuracy, yield, cost, etc. However, it has hardly been put into practical use in general consumer ICs.

Another method is to use a junction capacitor as the capacitor constituting the active filter, and to vary the capacitance value by utilizing the bias dependence of the absolute capacitance value of the junction capacitor, thereby absorbing variations in the absolute values of the resistance value and the capacitance value. Active 4 is an example of this.
An example of the BPF circuit is shown in FIG. 6 and will be described below. 5 is an input signal source, 6 is a variable voltage source, 7 is a differential amplifier with a gain of 3, 8 is an amplifier with a gain of 4 (K4-1), 9 is a gain Ks
, a differential amplifier 10, an output signal terminal 11, a constant voltage source 11, a resistor, a capacitance C1, and a capacitance C1 constitute the time constant circuit of the filter as in FIG. The resistors 1 to 1 are resistors, and the resistors 1 to 1 apply a DC potential to the input terminals of the amplifiers 7 to 90.

Capacitance C6 is a coupling capacitance. Note that the capacitances C, , C, are composed of junction capacitances. In the above configuration, if the amplifier is an ideal amplifier with infinite input impedance and zero output impedance, the terminal voltages at the input terminal of the differential amplifier 702 are always equal, and the output terminal voltage of the differential amplifier 7 is constant.

Therefore, due to the potential fluctuation of the variable voltage source 6, the capacitors C3 and C! The bias potential applied to both poles changes equally, and the absolute capacitance values of capacitors C2 and C1 change in accordance with the bias potential, so that variations in the time constant circuit can be absorbed. Further, if the amplifier 8 is a buffer circuit in which the input terminal potential and the output terminal potential are equal, the input terminal DC potentials of the two differential amplifiers 90 will also be equal, and the output terminal potential of the differential amplifier 9 will be constant.

Furthermore, if the output potential of the constant voltage source 11 is configured to be equal to the output terminal potential of the differential amplifier 9, the applied voltages of the capacitors Cs and 04 will change equally according to changes in the output potential of the variable voltage source 6, and The absolute value of capacitance also changes accordingly. Therefore, variations in the time constant circuit constituting the LPF section can be absorbed by adjusting the variable voltage source B.

However, the dependence of the junction capacitance on the bias voltage on the capacitance value has a characteristic as shown in an example shown in FIG. As can be seen from this figure, the sensitivity of changes in the absolute value of junction capacitance due to changes in bias voltage is low, and in FIG. 4, in order to change the capacitance value by ±35 degrees, the bias voltage must not be changed by about 4V.

For this reason, for example, when the power supply voltage is 5 µ, it is impossible to vary the potential of the variable voltage source 6 by 4 µ due to circuit operation margin constraints, and it is impossible to absorb the variation of ±65 µ in the time constant circuit. It becomes possible.

Therefore, an example of the time constant switching circuit shown in FIG.
It is provided in the time constant circuits of the PF section and LPF section to absorb variations in the time constant circuits.

FIG. 5 will be explained. a) in Fig. 5 is)l　P　F section.

b) is the time constant circuit of the LPF section. 12.13 is a time constant changeover switch, 14 is a changeover signal terminal, capacitance Ca, C
b corresponds to the capacity ftC1 in FIG. Resistors a and Rb correspond to the resistors in FIG. 6th
The resonance frequency f of the H P fi' part and the LPF part in the figure
on, foL and the quality of the circuit QHlQL are expressed as fOH-□...(1) 24haWpersonτ7, so the capacitance C of the resonance frequency fOH, fOL
By setting the capacitances Ca and Cb corresponding to 1 and the resistance, the resistance ratio a, and the absolute value of the rib to about +40 and about -25 degrees, respectively, the resonant frequencies foe and fOL are both about +15 compared to the center value. The person in charge is out of sync. Thereafter, by adjusting the junction capacitance and moving the resonant frequency fOH1fOL by a factor of ±20, it is possible to absorb the variation of ±65 in the time constant circuit.

However, if a time constant switching circuit as shown in Fig. 5 is provided, the ratio of capacitances C1 and C7 and the ratio of resistance to mass will change, as shown in (21, (2')), and the ratio of capacitance Ca to resistance will change. The value of Q, which indicates the quality of the circuit, will be different between the Ra side and the capacitor Cb and resistor Rb side.For this reason, an active BPF circuit as shown in Fig. 3 with a time constant switching circuit as shown in Fig. 5 is used. However, a problem arises in that the output signal amplitude varies due to variations in the Q value.

For example, if the above circuit is used in a home VTR, VHS (V
B P with a passing center frequency of 4.21■1z in the color signal processing system of the ideo Home System) method.
F (hereinafter abbreviated as 4.21MHz BPF).

At this time, in the multiplier that receives this BPF output as input, 4.
21M) Since the color signal is switched using the Jz signal,
4, 211 (z signal amplitude varies (and when the amplitude level is small, the conversion efficiency will decrease, and when the amplitude level is large, the 4.21 MHz 4't4 will leak and interfere with the color signal) These problems cause a drop in the S/N ratio of the color signal on the playback screen and a beat disturbance, making the playback screen of the VTR extremely unsightly.

[Purpose of the invention]

The object of the invention is to provide an active filter integrated circuit which eliminates the above-mentioned drawbacks.

[Summary of the invention]

The present invention is an active BPII with a built-in time constant switching circuit.
'The circuit configuration is such that the output signal level in the circuit fluctuates.

[Embodiments of the invention]

Hereinafter, a block diagram of an embodiment of the present invention will be explained with reference to FIG. In FIG. 6, the same reference numerals as in FIG. 5 and FIG.
Like numbers indicate like components. 16 is a limiter circuit, 1
5 is an output end.

As in this example, an active B P with a time constant switching circuit is used.
By coupling the limiter circuit 16 to the output terminal of F,
Variations in the output amplitude of the BPF1 path due to the switching operation can be suppressed.

4.21 Mk-Jz B of color signal processing circuit of VTR
By using the active BPF circuit of this embodiment in the PF, a good screen can be obtained that is free from S/N reduction and beat disturbance on the main screen.

FIG. 7 shows an embodiment of a limiter circuit used in the present invention. 15 is the output terminal, 16 is the limiter circuit, 17 and 18
is a constant current source, 19 is a smoothing capacitor, and 20 is a constant voltage W.
121 is a signal input terminal, 8-10 are resistors, and Q1-Q3 are transistors. The operation of the circuit shown in FIG. 7 will be explained.

An input signal from the signal input terminal 21 is inputted to the bases of transistors Q1 and Q2 constituting a differential amplifier via resistance ratios 8 and R9. However, since the capacitor t19 is connected to the lead end of the transistor Q2, the input signal is smoothed and the DC component is propagated. In the differential amplifier #jJ, the input signal difference is multiplied by the gain, but since this circuit has a high gain, the output signal has a waveform limited by the upper and lower limits, and is output from the emitter lower of the transistor Q3. Therefore, even if the amplitude of the input signal from the input terminal 21 varies, by making the gain of the differential amplifier sufficiently large, the output signal from the output terminal 15 becomes a signal with a constant amplitude applied by the limiter.

Fig. 6 shows an active BPF circuit with a built-in time constant switching circuit, and an amplifier with infinite input impedance.
Although we have proceeded with the discussion assuming an ideal amplifier with zero output impedance, in actual circuits, the input impedance is not infinite, and the output impedance is not zero. Further, characteristics of elements within the IC deteriorate and vary due to parasitic elements specific to integrated circuits. Therefore, even in an active BPF circuit as shown in Fig. 8 without a time constant switching circuit, the BP
Since the output signal amplitude at the F section varies, by adding the limiter circuit 16, it is possible to eliminate the variation in the output signal amplitude.

By adding a limiter circuit to the output of the PF section, odd-numbered harmonic components of the fundamental wave are generated as frequency components of the limiter circuit output signal, but they are out of the band of the VTR and do not pose a problem.

〔Effect of the invention〕

As explained above, according to the present invention, variations in output signal amplitude due to variations in the time constant circuit of an active BPF consisting of a resistor, a capacitor, and an amplifier can be absorbed by providing a limiter circuit in the BPF output section. An integrated active BPF circuit having a desired BPF percentage can be obtained, and a block filter, which has conventionally been an external component, can be integrated.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of an active BPF, Fig. 2 is a characteristic diagram of the filter shown in Fig. 1, Fig. 3 is a circuit diagram showing an example of an active BPF' circuit using junction capacitance, and Fig. 4 is a circuit diagram showing an example of an active BPF' circuit using junction capacitance. A special diagram of junction capacitance, Figure 5 is a circuit diagram showing an example of a time constant switching circuit, and Figure 6 is an active B adopting the present invention.
FIG. 7 is a circuit diagram showing an example of a limiter circuit, and FIG. 8 is a circuit diagram showing another example of an active BPF circuit using the present invention. Mass, Tame IR51 wind, Ra, 几b... Tokiya number is composed of 1-
Resistance, C,, C,, C,, C,, Ca, Cb - Capacitance constituting time constant, 6...q variable voltage source, 12, 13-06 Time constant switching circuit, 16...・Limiter circuit. Kueto Patent Attorney Akio Takahashi% 1 l No. ? Sen No. 3 l No. 50 No. 4

Claims (1)

[Scope of Claims] 1. An integrated circuit comprising an active bandpass filter constructed on a semiconductor wafer and comprising a resistor, a capacitor, and an amplifier, characterized in that a limiter circuit is provided at the output stage of the bandpass filter. 2. In a magnetic recording and reproducing device that records and reproduces a color signal by frequency converting it to a low frequency, the integrated device according to claim 1, wherein the output signal of a multiplier that generates a carrier wave for frequency conversion is used as an input signal. circuit.