JPH06105852B2 - Modulation / demodulation circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a modulation / demodulation circuit in which the modulation and demodulation circuits formed on the same semiconductor substrate can be easily adjusted.

[Technical background of the invention]

Along with the high integration of semiconductor integrated circuits, in recent years, it has been frequently practiced to incorporate a time constant circuit capacitive element in the integrated circuit.

The capacitive element built in the semiconductor integrated circuit IC generally has a structure as shown in FIG. That is, FIG. 4 shows a capacitive element having a MOS structure formed by the Al layer-insulating layer-semiconductor layer n ⁺ . Although the area (Al on the left side) of this capacitive element has high accuracy, the thickness and dielectric constant of the insulating layer have considerable variations. Therefore, the capacitance value varies within the range of ± 20% to 30%.

FIG. 5 shows an example of a conventional circuit using such a capacitive element as a capacitive element of a time constant circuit in a semiconductor integrated circuit.

The circuit shown in FIG. 5 has a plurality of (n) time constant circuits CkT ₁ to CkTn in _one semiconductor integrated circuit. Then, each time constant circuit CkT ₁ ~CkTn each having a capacitive element C ₁ to Cn.

The capacitance values of these capacitive elements C _{1 to} Cn vary within a range of ± 20 to 30%, so if the time constant circuits CkT _{1 to} CkTn are accurately matched to desired values (design values), It is necessary to provide terminals T _{1 to} Tn respectively, connect variable resistors VR _{1 to} VRn to each of them, and obtain design values by adjusting the resistance values.

[Problems of background technology]

However, as described above, in the configuration in which the time constant is provided for each time constant circuit CkT _{1 to} CkTn, the time constant circuit is
As CkT _{1 to} CkTn increase, the number of terminals and variable resistance increases. Thus, increasing the circuit scale, and further, each time constant circuit CkT ₁ ~CkTn, it is necessary to adjust the time constant, causes an increase in the adjustment step, it is extremely uneconomical.

[Object of the Invention]

INDUSTRIAL APPLICABILITY The present invention applies the fact that the time constant adjusting unit of a plurality of time constant circuits as described above can be made common to facilitate adjustment of the oscillation frequency and demodulation sensitivity of the modulation and demodulation circuits formed on the same semiconductor substrate. It is an object of the present invention to provide a modulation / demodulation circuit that can be obtained.

[Outline of Invention]

The present invention is a modulation circuit using a multivibrator,
A pulse count type demodulation circuit and a connection circuit for connecting a current source that determines the oscillation frequency of the modulation circuit and a current source that determines the pulse width of the demodulation circuit with a current mirror are provided.
The modulation circuit, the demodulation circuit, and the connection circuit are formed in the same semiconductor integrated circuit device, and the other is adjusted by adjusting either the oscillation frequency of the modulation circuit or the demodulation sensitivity of the demodulation circuit. It is configured to be automatically adjusted.

Example of Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram on which the present invention is based.

In FIG. 1, CkT _{1 to} CkTn are time constant circuits built in this semiconductor integrated circuit IC. Time constant circuit CkT _{1 to} CkTn
Have capacitive elements C _{1 to} Cn, respectively.

Each of the capacitive elements C _{1 to} Cn has a current source transistor Q ₁ to
It is connected to the collector of Qn. Each transistor Q ₁ ~Qn
The emitters of are connected to the power supply V _CC through resistors R _{1 to} Rn, respectively. The base of all the transistors Q ₁ Qn are commonly connected to the base of the transistor Q ₀ of the diode connection. The emitter of this transistor Q ₀ is a resistor R ₀
Connected to the power supply V _CC via. The common connection point between the base of the transistor Q ₀ and the core is
It is connected to the collector of a transistor Q having a polarity opposite to that of Q _{0 to} Qn. The emitter of the transistor Q is connected to the terminal T _0, The terminal T _0, the variable resistor VR ₀ is external. A bias power supply V _B is connected to the base of the transistor Q.

In the above structure, the transistor Q ₁ Qn corresponding to the time constant circuit CkT ₁ ~CkTn each form a transistor Q ₀ and a current mirror circuit. That is, these current mirror circuits use the collector of the transistor Q ₀ as a common input terminal,
The collectors of the transistors Q ₁ Qn the respective output terminals. The current mirror ratio of each current mirror circuit is set by the resistance ratio of the resistor R ₀ and the resistors R _{1 to} Rn. For example, the transistor related to the time constant circuit CkT ₁
The current mirror ratio of the current mirror circuit formed by Q ₀ and Q ₁ is determined by the ratio of resistors R ₀ and R ₁ . The ratio of the current mirror ratios among the plurality of current mirror circuits is determined according to the ratio of the time constants among the time constant circuits CkT _{1 to} CkTn. Then, the input current at the common input end of the plurality of current mirror circuits is adjusted by the variable resistor VR ₀ .

The operation of the above configuration will be described. In a semiconductor integrated circuit, generally, the characteristics of each element largely vary as described above, but if the elements are of the same kind, the fluctuation tendency is almost the same (there is a pair property). Therefore, the characteristic ratio between elements of the same type can always be a desired value regardless of variations in the characteristics of the elements. Therefore, at the design stage, when the capacity ratio and the resistance of the resistance ratio of the time constant circuit Ckt ₁ capacitive element C ₁ constituting the ～CkTn to Cn, by setting in accordance with a desired time constant, even if variations in device characteristics The desired time constant can be obtained. Similarly, by appropriately setting the resistance values of the resistors R _{0 to} Rn in accordance with the desired time constant ratio, the ratio of the current mirror ratios among the plurality of current mirror circuits can also be increased. It can be adjusted to a constant ratio. Furthermore, by setting the element characteristics in this way, the ratio of the time constants among the plurality of time constant circuits configured by the respective current mirror circuits and the corresponding capacitance elements C1 to Cn is also the desired time constant. Will match the ratio. Therefore, the time constant circuit CkT ₁ ~
If at least one of the time constants of CkTn is measured and the input current of the current mirror circuit is adjusted by the variable resistor VR ₀ so that this value becomes a desired value, all the time constant circuits CkT _{1 to} CkTn can be adjusted at once. The time constant of can be accurately set to a value.

As described in detail above, this embodiment is provided with each time constant circuit CkT ₁ ~
A current mirror circuit is provided for each CkTn, the input ends of these current mirror circuits are made common, and the ratio of the current mirror ratio between the current mirror circuits is adjusted to the time constant ratio between the time constant circuits CkT _{1 to} CkTn. It was done like this. According to such a configuration, all the time constant circuits CkT _{1 to} CkTn are provided by only providing one variable resistor VR ₀ that adjusts the input current at the common input end of the plurality of current mirror circuits.
The time constant of can be adjusted. Moreover, there is an advantage that this adjustment is performed all at the same time. As a result, the time constant circuit
When CkT _{1 to} CkTn are built in an integrated circuit IC, even if the number increases, the number of terminals T ₀ and variable resistors VR ₀ does not increase, preventing an increase in circuit scale and manufacturing cost. be able to.

FIG. 2 is a circuit diagram showing an example of a specific configuration of the bias power supply V _B. The bias power supply V _{B in} FIG.
Of the base-emitter voltage, the variation of the collector current of the transistor Q due to the temperature drift, and the variation of the time constant due to the temperature drift.

That is, the illustrated circuit has a diode-connected transistor Q ₀ and a resistor R _0, and a transistor Q _A and a resistor R _A that form a current mirror circuit. The collector of the transistor Q _A is connected to the common connection point of the base and collector of the transistor Q _B , which has the same polarity as the transistor Q and is diode-connected. The emitter of the transistor Q _B is grounded via the resistor R. The base of transistor Q _A is then connected to the base of transistor Q ₀
The common connection point between the base and collector of Q _B is transistor Q
Connected to the base of.

In the above configuration, the collector voltage of the transistor Q _A becomes the bias voltage of the transistor Q. So the resistance R ₀ , R
_The above-described compensation can be completely realized by setting the following relationship in the ratio of the resistance of _A and the emitter area AE of the transistors Q _A , Q ₀ , Q _B , and Q.

R ₀ : R _A = AE (Q _A ): AE (Q ₀ ) = AE (Q _B ): AE (Q)
(1) FIG. 3 shows an embodiment of the present invention, which is an example applied to a luminance signal FM modulator and an FM demodulator of a video tape recorder.

In FIG. 3, transistors Q ₁₁ , Q ₁₂ and resistors R ₁₀ , R _{11 are shown.}
Constitutes the bias circuit 11. Transistors Q _{M1 to} Q _M6 ,
The emitter-coupled astable multivibrator including the resistors R _{M1 to} R _M4 and the capacitive element C _M constitutes the FM modulator 12. An emitter-coupled monostable multivibrator 131 including transistors Q _{D1 to} Q _D6 , resistors R _{D1 to} R _D4 and a capacitor CD, and a multiplier 13
2 constitutes the FM demodulator 13.

Further, the modulation input terminal Ta of the semiconductor integrated circuit IC is connected to the power supply V _CC via the sync chip carrier adjustment variable resistor VR _C. This input terminal Ta is connected from the video signal source Si during recording. A video signal having a DC level of is input via a deviation adjusting variable resistor VR _D. The modulated output (FM video signal) of this video signal is output from the output terminal Tb. During reproduction, the demodulated output of the FM video signal is guided to the terminal 15 from the demodulated pulse output terminal Tc via the external low-pass filter 14.

The operation of the above configuration will be described.

First, the FM modulation operation in the recording mode R will be described.
In this case, since the mode instruction signals S ₁ and S ₂ are at high level, respectively, the transistor Q _D6 is turned off and the transistor Q _M6 is turned off.
Turns on. Also, the bias circuit 11 causes the emitter potential of the transistor Q _M3 to Is set to. Therefore, the direct current does not flow through the variable resistor VR _D , but only the alternating current flows.

Here, the current I _M driving the emitter-coupled astable multivibrator is Becomes The first term on the right side of the above equation is a direct current component, and the second term is an alternating current only. Since the oscillation frequency of F _M modulator 12 with a time constant determined by the current I _M and the capacitance element C _M is determined, the capacitance value of the capacitive element C _M is also varied in the range of 20 to 30% ±, By adjusting the variable resistors VR _C and VR _D , it is possible to adjust to the specified sync chip carrier frequency and deviation.

On the other hand, in F _M demodulation operation of reproduction mode P, the transistor Q _M6 is turned off, the transistor Q _D6 is turned on. As a result, the emitter potential of the transistor Q _D3 becomes Is set to. At this time, the amplitude of the video signal from the signal source Si is set to O (as set by the semiconductor integrated circuit forming the signal source (Si)), and the variable resistance VR
_No current flows through _D. Therefore, the current I _D driving the emitter-coupled monostable multivibrator is Becomes The above formula represents the direct current. Demodulation sensitivity of F _M demodulator is determined by the time constant determined by the capacitance value of the current I _D and the capacitor C _D.

Here, since the capacity of the capacitor C _D will have a variation of ± 20 to 30%, relative accuracy (pairability) of the capacitor element C _M is good, the adjustment of the F _M demodulator 13, varied capacity Element C _M
If the resistance value of the variable resistor VR _C is properly adjusted with respect to the capacitance value of, when this resistance value is directly substituted into the equation (3), it is determined by the current I _D and the capacitance C _D. The constants vary little.

In the above description, when the parts related to the present invention are summarized, the FM which is desired to have all the circuit constants of the circuit shown in FIG.
By determining the oscillation frequency of the modulator 12 and the demodulation sensitivity of the FM demodulator 13, even if the capacitance elements C _M and C _D with extremely large variations in capacitance value (absolute value) are used, By adjusting the oscillation frequency during FM modulation operation to the desired value with the variable resistor VR _C , the demodulation sensitivity of the FM demodulation operation almost matches the desired value.
The capacitance value of C _D variation of the demodulation sensitivity caused by variations in the (absolute value) does not occur. At this time, variations in demodulation sensitivity include variations in the capacitance value ratio of the capacitive elements C _M and C _D , and resistances R _M2 and R _M3.
It is determined by the variation in the resistance ratio of the resistors and the variation in the resistance ratio of the resistors R _D2 R _D3 , but the variation in the ratio of the characteristics of these similar elements is extremely small in the semiconductor integrated circuit.

Note that the demodulation sensitivity during FM demodulation operation is set to the desired value by adjusting the oscillation frequency during FM modulation operation to the desired value with the variable resistor VR _C. Is adjusted to a desired value (also performed by the variable resistor VR _C ), which means that the oscillation frequency during the FM modulation operation is set to a desired value.

As described above, when the present invention is applied to the adjustment of the time constant of the time constant circuit of the FM modulator 12 for the VTR luminance signal and the time constant circuit of the FM demodulator 13, the time constant of the FM modulator 12 is adjusted. The time constant of the FM demodulator 13 is automatically set to a desired value only by setting the oscillation frequency to a desired value, and the demodulation sensitivity is also set to the desired sensitivity.

Of course, the present invention can be applied to the adjustment of the time constant of a time constant circuit other than the time constant circuit which is made into a semiconductor integrated circuit.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide a modulation / demodulation circuit in which the oscillation frequency and the demodulation sensitivity of the modulation and demodulation circuits formed on the same semiconductor substrate can be easily obtained.

[Brief description of drawings]

1 is a circuit diagram on which the present invention is based, and FIG. 2 is a circuit diagram showing an example of a specific configuration of the bias power supply shown in FIG.
FIG. 3 is a circuit diagram showing an embodiment of the present invention, FIG. 4 is a diagram showing a semiconductor integrated circuit structure of a capacitor, and FIG. 5 is a circuit diagram showing a conventional device. CkT _{1 to} CkTn …… Time constant circuit, C _{1 to} Cn …… Capacitance element, R ₀ 〜
Rn ...... resistance, Q _1, Q ₀ ~Qn ...... transistor, V _B ...... bias power, VR ...... variable resistance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H03K 7/06 7402-5J 17/28 G 9184-5J

Claims (1)

[Claims] 1. A modulation circuit using a multivibrator, a pulse count type demodulation circuit, an adjustable first current source, and a current source having a first current value that determines an oscillation frequency of the modulation circuit. And a third current source that determines the pulse width of the demodulation circuit and that has a current value that follows the first current source, the modulation circuit, the demodulation circuit, and the first current source. To adjust the first current source by forming the third current source in the same semiconductor integrated circuit device and observing either the oscillation frequency of the modulation circuit or the demodulation sensitivity of the demodulation circuit. so,
A modulation / demodulation circuit characterized in that the other is automatically adjusted.