JPH1155109A - Current source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current source circuit with which the temperature fluctuations of a current for regulating the center frequency of a voltage controlled oscillator(VCO) is compensated against with respect to the change in a surrounding temperature, while using a resistor of the same kind as a resistor of serial monolithic IC electronic circuit in a frequency modulating system. SOLUTION: A current source 1 which does not fluctuate in current value due to temperature and a current source 2 with current values proportional to temperatures are connected serially, and a correction current source circuit, which is provided with a diode 6 for limiting the direction of a differential current generated between them and a PNP transistor 4 for preventing the saturation of a current source 1, is added to a known current source circuit to be corrected for generating a current with a resistance value and a control voltage. Thus, the temperature fluctuation of a center frequency f0 due to a secondary temperature coefficient of resistance is corrected by first-order diagonal approximation, and the temperature fluctuation can be decreased significantly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator which mainly performs frequency modulation for processing a stereo audio signal of a VTR.
The present invention relates to a current source circuit for performing temperature compensation of a current supplied to a (VCO) and determining a value of a center frequency (hereinafter, referred to as f ₀ ).

[0002]

F ₀ of the Related Art VCO used in stereo audio signal processing of the VTR is in the VHS standard, TYP ± 10 kHz
The strictest PAL method is ± 0.56
% Accuracy is required. In recent years, there has been a tendency to realize non-adjustment while maintaining the required accuracy. For this purpose, a PLL, that is, a phase locked loop or a zener zapping technique has been used. Zener zapping technology is a technology that applies a reverse bias to the emitter-base diode part inside the bipolar transistor and destroys the emitter-base junction with a strong electric field to short-circuit. Is what makes it possible. That is, in the circuit system shown in FIG. 5, the above-mentioned non-adjustment becomes possible by writing data into the ROM. VCO f
_{In order} to simultaneously perform the temperature compensation of _0, the resistance 1 shown in FIG.
9, a VCO adjustment current source is configured by using a resistor having a small temperature coefficient and high precision. Hereinafter, a description will be given of a temperature compensation method for f ₀ of the conventional VCO.

[0003] In FIG. 5, the adjustment current source output terminal of the f ₀ of VCO 7, 19 are and accurate resistance small temperature coefficient. The modulated current signal is input to the modulated current signal input terminal 12.
Is more input, is mixed with the aforementioned f ₀ adjustment current, VCO 1
Entered in 5. Since the oscillation frequency of the VCO 15 changes in proportion to the amplitude of the modulated current signal, it is output from the frequency modulation output terminal 16 as a frequency-modulated signal centered at f ₀ .

[0004] Adjustment of f _0, the modulated signal is monitored frequency modulation output terminal 16 when the no input, so that f ₀ is within the standards listed above, a value that determines the output of the D / A converter 17 Is written in the ROM 18 to complete the process.

In general, as for the oscillation frequency output f of the VCO, the following relationship is established between the VCO input current I and the capacity value C charged and discharged.

[0006]

F∝I / C The input current I of the VCO is represented by the sum of the modulated signal input I ₁ and the f ₀ adjustment current I _{0. When} the modulated signal is not input, the following equation is obtained from (Expression 1). Holds.

[0007]

## EQU2 ## f₀∝I₀/ C On the other hand, f₀Adjustment of the D / A converter at the time when is adjusted
Terminal 11 f₀Control voltage to V ₀And the current converting resistor 19
Assuming that the resistance value is R, f₀Adjustment current I₀Is given by
You.

[0008]

I ₀ = V ₀ / R Therefore, (Equation 2) can be rewritten into the following equation using (Equation 3).

[0009]

F ₀ ４V ₀ / (R × C) Since the temperature fluctuations of V ₀ and C can be ignored, the temperature compensation of f ₀ is performed by using a resistor having a small temperature coefficient as the resistor 19. Becomes

[0010]

However, in the conventional configuration, it is necessary to select an element having an extremely small temperature coefficient as a resistor as described above. Inevitably, when a monolithic IC is formed, external components are required. I had to be. Also, the external components of a resistor, while satisfying the f ₀ standard of the aforementioned accuracy, precision of approximately ± 0.1% is required in order to ensure compatibility of the data, as inevitably parts to its It became expensive.

Thus, the present invention is directed to overcoming the above-mentioned problems in the prior art, and has as its main object the same as the resistors included in a series of monolithic IC electronic circuits constituting a frequency modulation system. be used type of resistor Incidentally, to provide a f ₀ can be compensated for temperature variations of the adjustment current, temperature compensation current source circuit with utility in the new to changes in ambient temperature is there.

[0012]

SUMMARY OF THE INVENTION A temperature compensation current source circuit according to the present invention for solving the above-mentioned problem firstly applies a voltage to both ends of a resistor having at least a first-order temperature coefficient. In a current source circuit for taking out a current corresponding to the value of the voltage to an output terminal pair, the current of the output terminal pair is changed at a predetermined temperature as a fixed current and according to the first-order temperature coefficient. Outputs a current that is approximated by a temperature change current, the direction of increase or decrease with respect to the temperature change is opposite to that of the primary temperature change current, and is substantially equal to the difference current value between the fixed current and the primary temperature change current. A temperature compensating circuit connected in parallel to the resistor or the output terminal pair, and secondly, the temperature compensating circuit outputs a current substantially fixed with respect to temperature. And a first current source A second current source connected in series and outputting a current proportional to the temperature, and a diode connected at one end to a connection between the first and second current sources and limiting a direction of a difference current generated at the connection. And the other end of the diode is connected to one end of the resistor.

[0013] Thus, using a series resistor of the same type of circuit of resistors for performing frequency modulation, the current source circuit having a temperature compensation function of compensating for temperature variations of f ₀ adjusting current to a change in ambient temperature Is obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, the current source circuit to be compensated for is formed by using an ordinary resistor having a large temperature coefficient as known per se, Is provided with a first current source that does not fluctuate in temperature and a second current source whose current value is proportional to the temperature are cascaded to prevent saturation of the diode and the current source 1 that limit the direction of a difference current generated therebetween. are those obtained by adding the correction current source circuit having a PNP transistor in parallel with this the correction current source circuit, the action that effectively compensate for temperature variations of f ₀ adjustment current generated in a conventional current source part Having.

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

FIG. 1 shows an embodiment of a current source circuit having a temperature compensation function according to the present invention. In FIG. 1, reference numeral 1 denotes a current source which does not fluctuate in temperature, and 2 denotes a current source whose current value is proportional to temperature. 3, 3 and 5 are reference voltage terminals, 4 is a PNP transistor for preventing saturation of the current source 1, 6 is a diode for limiting the direction of current output, 7 is an output terminal of the current source, 8 is an NPN transistor, and 9 is a resistor. , 10 are operational amplifiers, and 11 is a current adjustment terminal.

The current source comprising the NPN transistor 8, the resistor 9 and the operational amplifier 10, that is, the current source circuit to be corrected has the same configuration as the conventional one, but the f ₀ adjustment generated by the temperature fluctuation of the resistor 9 used. For current temperature fluctuation,
A correction current source configured to limit the difference current between the current sources 1 and 2 in one direction by the diode 6 and to add the current to the current source to be corrected for correction.

The operation of the current source circuit having the temperature compensation function of the present invention configured as described above will be described below.

Firstly, conventional current source arrangement portion excluding the correction current source circuit for outputting a correction current to the temperature, i.e. the temperature of the f ₀ adjustment current when using the resistance is not negligible temperature coefficient in the correction current source circuit The variation is shown as follows.

The change in the resistance value with respect to the ambient temperature T _a of the diffusion resistance that is formed on the monolithic IC, the reference temperature 25 ° C.
The resistance value as the reference resistor R ₁ is generally represented by the following equation.

[0021]

R = R ₁ × {T _c1 × (T _a −25) + T _c2 × (T _a −25) ²で where T _c1 is a first-order temperature coefficient, and T _c2 is a second-order temperature coefficient. It is.

The output current of the current source output terminal 7 in FIG. 1 when the addition of the correction current is neglected is calculated by equation (3) and has a quadratic function characteristic with respect to the ambient temperature as shown in FIG.

[0023] If the ambient temperature range of practical use from T _a1 to T _a2, adjusting the current value I ₀₁ properties o'clock T _a1 The quadratic function and T _a = 25 ° C. during the adjustment current I _{0 (25)} to be approximated as a broken line in FIG. 3 by a linear function with a line using the adjustment current I ₀₂ o'clock T _a2. F ₀ Adjustment current in the primary function part having the temperature characteristics when normalized by I ₀₁ is expressed by the following equation.

[0024]

I ₀ = a × (T _a −25) / (T _a2 −25) + b where a = I _{0 (25)} −I ₀₂ and b = I ₀₁ −I _{0 (25)} .

The opposite polarity of the current of the current type is shown in Figure 4, be added to this as a correction current, it can greatly reduce the temperature change of the f ₀ adjustment current in the temperature range of practical use and Become. Therefore, the added correction current source circuit will be described below.

The first current source 1 in FIG. 1 is a current source having no temperature fluctuation, and is generally easily formed using a bandgap reference voltage circuit. On the other hand, the current source 2 proportional to the temperature can be easily formed by extracting the circuit current of the above-described bandgap reference voltage circuit with a current mirror. FIG. 2 shows an example of the configuration of these current sources. The current source output terminal 20 corresponds to the terminal 20 of the output section of the first current source 1 in FIG. Corresponds to the terminal 21 of the output section of the second current source 2 in FIG.

In FIG. 1, the difference current between the current source 1 and the current source 2 is supplied through the diode 6 only when the current value of the current source 2 is larger than the current value of the current source 1. You. That is, this is for giving the linear correction characteristic to the primary correction current.

The current I _T of the current source 2, which is proportional to the temperature,
The use of a current proportional to the flow temperature in a bandgap circuit is generally represented by the following equation.

[0029]

I _T = K × V _T / R _T × InN = K ′ × (T _a −25) + b where R _T is the ground emitter resistance of the bandgap circuit, and N is the transistor area ratio; k the Boltzmann constant, when the absolute temperature, and electron charge amount q T, the voltage V _T is given by V _T = kT / q. Also, K is equivalent to the current mirror ratio which is schematically decided by a ratio of percentage change clogging resistance from the band gap current value to a final current source output of R _T and R _X. Assuming that K ′ is a constant based on 25 ° C. and that the fixed current value of the current source 1 is I _C , the difference current I _H, which is the correction current, is expressed by the following equation.

[0030]

I _H = K ′ × (T _a −25) + b−I _{C For} the correction current of the first-order polygonal line, the gradient of the difference current with respect to the temperature is created by the current value of the current source 2, and the correction current is set to 0. Is set by the current value of the current source 1.

The PNP transistor 4 shown in FIG.
Is larger than the current value of the current source 2, the current source 1 does not saturate, so that the difference current is bypassed, that is, the potential of the current source connection is connected via the PNP transistor 4 to the reference voltage terminal 5. This is fixed at a value corresponding to the voltage.

As described above, according to the present embodiment, the first current source whose current value does not fluctuate with temperature and the second current source whose current value is proportional to temperature are connected in cascade, and the difference Diode for limiting direction and PNP for preventing saturation of current source 1
By adding a corrected current source circuit having a transistor to a corrected current source circuit that generates a current with a resistance value and a control voltage, the temperature variation of the current caused by the second-order temperature coefficient of the resistance is represented by a linear line. By approximation and correction, the temperature fluctuation of f ₀ can be greatly reduced.

[0033]

As apparent from the above description, the present invention comprises a cascade connection of a first current source whose current value does not fluctuate with temperature and a second current source whose current value is proportional to temperature. By adding a correction current source circuit having a diode for limiting the direction of the generated difference current and a PNP transistor for preventing the saturation of the current source to a current source circuit to be corrected for generating a current with a resistance value and a control voltage, A current having a temperature compensation function excellent in usefulness, in which the temperature fluctuation of the center frequency f ₀ adjusting current caused by the secondary temperature coefficient of the resistor is corrected by a first-order linear approximation and the temperature fluctuation can be greatly reduced. This realizes a source circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a current source circuit having a temperature compensation function according to an exemplary embodiment of the present invention.

FIG. 2 is an example of a specific circuit diagram of a current source used in the embodiment of the present invention.

FIG. 3 is an adjusted current characteristic diagram of f ₀ approximated by a broken line in one embodiment of the present invention.

FIG. 4 is a characteristic diagram of a temperature compensation current portion according to the present invention.

FIG. 5 is a block diagram of a frequency modulation method showing a conventional temperature compensation method of this kind.

[Explanation of symbols]

1, 2, current source 3, 5, reference voltage terminal 4, PN
P transistor, 6 diode, 7 current source output terminal, 8 NPN transistor, 9, 19 resistor
10: operational amplifier, 11: current adjustment terminal, 12: modulated signal input terminal, 13: mixed circuit, 14: capacitance, 15: VC
O, 16: frequency modulation output terminal, 17: D / A converter,
18… ROM, 20, 21… Current source output terminals.

Claims (2)

[Claims] 1. A current source circuit for applying a voltage to both ends of a resistor having at least a first-order temperature coefficient and extracting a current corresponding to a value of the voltage to an output terminal pair, wherein the current of the output terminal pair is set to a predetermined value. Approximate with a fixed current and a primary temperature change current that changes according to the primary temperature coefficient at the boundary of the temperature, and the direction of increase or decrease with respect to the temperature change is opposite to that of the primary temperature change current. And the fixed current and the 1
A current source circuit comprising: a temperature compensating circuit that outputs a current substantially equal to a difference current value of a next temperature change current, connected in parallel to the resistor or the output terminal pair. 2. The temperature compensation circuit according to claim 1, wherein the first current source outputs a current substantially fixed with respect to the temperature, and a second current source connected in cascade with the first current source and outputs a current proportional to the temperature. A current source; and a diode having one end connected to a connection portion of the first and second current sources and limiting a direction of a difference current generated in the connection portion, and the other end of the diode connected to one end of the resistor. 2. The current source circuit according to claim 1, wherein: