JP2018147129A - Reference current source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reference current source circuit to solve a problem: that is, a reference voltage generally uses a circuit configuration called bandgap reference that generates little fluctuation of voltage, but a reference current source and/or a clock source have had difficulty in achieving a required accuracy because the characteristic values of components used were degraded due to ambient temperatures and long-term operations.SOLUTION: A current source correction circuit 1 comprises: an oscillation circuit 200 to be driven by current; a reference current source 100 for supplying the current to the oscillation circuit 200; an input of a reference period to be supplied from outside an integrated circuit; and a period comparator 300 for adjusting a reference current so that the periodic difference of the first and second inputs is within an adjustable minimum range when the output period of the oscillation circuit 200 is a first input and the reference period is a second input.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reference current source circuit built in an integrated circuit, and more particularly to a method for correcting a reference current.

  As a background art in this technical field, there is a publication of JP-A-2015-1745 (Patent Document 1). This publicity includes: “Calculate the frequency of the first clock signal using the oscillator that generates the first clock and the second clock signal input from the outside of the display driver IC, and calculate the target frequency and the calculated frequency. And an oscillator that adjusts the frequency of the first clock signal based on the adjustment signal ”(see summary).

JP2015-1745

  In mixed signal LSIs, a reference voltage source and a reference current source with small characteristic fluctuations due to environmental changes and deterioration over time are important in order to ensure the absolute value accuracy of voltages and currents of analog circuits. In order to ensure the timing accuracy of the digital signal, a clock source serving as a reference time is important.

  FIG. 2 is an example of a circuit diagram of a conventional reference current source. In the reference current source circuit shown in the example, a reference voltage source 101 that supplies a reference voltage V1, a resistance element 103 for converting the reference voltage into a current, and a voltage V2 applied to the resistance element 103 are made equal to the reference voltage V1. The error amplifier 102 and the NMOS 104, and the current mirror circuit 105 for distributing the current flowing through the resistor 103 to the oscillation circuit and other analog circuits.

  Here, when the resistance value of the resistance element 103 is R and the reference current is I, the reference current is expressed by I = V1 / R.

  Among these, for the reference voltage V1, by using a circuit configuration generally known as a bandgap reference, a voltage with a small variation in which the temperature dependence of the element is canceled is generated.

  However, the value of the reference current varies depending on the resistance value of the resistance element due to environmental temperature or deterioration due to long-term operation.

  For this reason, the accuracy of the reference clock by the reference current and the oscillation circuit using the reference circuit in the reference circuit is more affected by the characteristic variation of the resistance element than the reference voltage, and it is difficult to increase the accuracy.

  Patent Document 1 describes a method of obtaining a clock source that is stable with respect to manufacturing errors of used elements and temperature changes by using an external clock. However, the method of Patent Document 1 is intended only for correcting the clock source in the reference circuit, and cannot correct the reference current.

  Therefore, the present invention provides a correction method that corrects not only the clock source but also the reference current source by using an external clock.

  In order to solve the above problems, the present invention provides an oscillation circuit driven by current, a reference current source for supplying current to the oscillation circuit, an input of a reference period supplied from outside an integrated circuit, and the oscillation A comparator that adjusts the reference current so that the output period of the circuit is a first input, the reference period is a second input, and the first second period difference is within a minimum adjustable range; Have

  According to the present invention, it is possible to provide a reference current source that does not depend on temperature change or aging deterioration of an element by using an external clock.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is an example of the block diagram showing the correction system of this invention. It is an example of the schematic of the circuit showing a 1st Example. It is an example of the oscillation circuit used for a 1st Example. It is an example of the timing chart of the oscillation circuit used for a 1st Example. It is an example of the circuit structure showing a 2nd Example. It is an example of the circuit structure showing a 3rd Example. It is an example of the circuit structure showing a 4th Example. It is an example of the timing chart explaining a 4th example.

  Examples will be described below with reference to the drawings.

FIG. 1 is an example of a configuration diagram showing a correction method of the present invention. The current source correction circuit 1 includes an oscillation circuit 200 driven by a current, a reference current source 100 that supplies current to the oscillation circuit, an input of a reference period that is supplied from outside the integrated circuit, and an output of the oscillation circuit A period comparator 300 that uses a period as a first input, uses the reference period as a second input, and adjusts the reference current so that the first and second period differences are within a minimum adjustable range; The reference current source 100 has a variable current value to be supplied, and has a function of controlling the current value by a control signal from a comparator 300 described later.

  The oscillation circuit 200 uses a circuit whose output clock cycle is inversely proportional to the current value supplied by the reference current source 100. That is, assuming that the clock cycle is T1, the supply current value of the reference current source is I1, and the proportionality coefficient between them is A, the relationship is expressed as T1 = A / I1.

  The comparator 300 compares T1 and T2 when the reference period acquired from the outside of the current source correction circuit 1 is T2. If T1 <T2, the comparator 300 outputs a control signal for decreasing I1, and T1> If it is T2, a control signal for increasing I1 is output.

  Further, the proportional coefficient A has a function of selecting a value in advance in order to set the reference current I1 to a desired value when T1 = T2.

  The effects of this example are shown below.

  Assume that the proportional coefficient A is selected so that the relationship of T2 = A / Iref is established, where Iref is a target desired current value.

  Here, consider a case where the reference current I1 fluctuates by ΔI due to the influence of the environmental temperature, the change of the element over time, and the like, and I1 = (Iref + ΔI).

  At this time, T1 = T2 / (1 + ΔI / Iref) is derived from the relationship of T1 = A / I1 = A / (Iref + ΔI). Therefore, if ΔI is positive, T1 <T2, and if ΔI is negative, T1> T2. If ΔI = 0, T1 = T2.

  On the other hand, if T1 <T2, the comparator 300 controls the reference current source 100 so as to decrease I1, and conversely if T1> T2, it controls the reference current source 100 so as to increase I1. To do.

  Therefore, if I1 increases by ΔI from Iref, T1 <T2, and I1 decreases until T1 = T2, and conversely, if I1 decreases by ΔI from Iref, T1> T2, and again T1 I1 increases until = T2.

  Thus, since negative feedback is applied so that the relationship of T1 = T2 is maintained, the relationship of T2 = A / Iref can be maintained. Here, when Iref is summarized, Iref = A / T2, and the value of Iref is determined by the proportional coefficient A and the reference period T2 acquired from the outside. In addition, high-precision ones may be selected, and these can be selected regardless of the resistance element of the reference current source.

  Here, a specific example of the proportional coefficient A will be described using an example of the oscillation circuit 200. FIG. 3 is an example of the oscillation circuit 200.

  The oscillation circuit 200 is configured to receive the reference voltage V1 and the reference current I1 and output a clock cycle to the OUT terminal. This circuit includes capacitive elements C1 and C2, a current mirror circuit 201 for copying the reference current I1 to the charge current I2 and discharge current I3 of the capacitor, a switch circuit SW1 for switching the I2 and I3, and V4 A non-inverting circuit comprising a non-inverting comparator circuit CMP1 for monitoring the voltage and switching the switch, and an OPA1 for generating the operating voltage V3 of the oscillating circuit from the VIN, and a non-inverting circuit R1 and R2. An amplifier circuit portion is included.

  FIG. 4 is an example of a timing chart of the oscillation circuit 200.

  In the above circuit configuration, if I1 = I2 = I3, the output oscillation period T1 is expressed by T1 = V3 × 2 × C1 / I1. Further, V3 = V1 × (R1 + R2) / R1 by a non-inverting amplifier circuit. Now, if the ratio of R1 and R2 is set to 1: α and V3 is substituted into the equation of T1, T1 = V1 × It can be expressed as (1 + α) / α × 2 × C1 / I1. From the above, the relationship of A = V1 × (1 + α) / α × 2 × C1 is obtained.

  Since the reference voltage V1 is constant in the above relational expression, the value of A can be arbitrarily varied by switching the R1: R2 ratio or the value of C1.

  The switching method can be realized, for example, by electrically switching a plurality of resistance elements or capacitance elements connected in series or in parallel by a MOS switch.

  At this time, if the constant (1 + α) / α × 2 determined by the R1: R2 ratio is β, Iref = A / T2 = V1 × β × C1 / T2, In comparison, it can be said that R is replaced by T2 / C1.

  In the above, for example, a communication signal can be used as the reference period T2. Taking an example of an in-vehicle control unit network, communication between units and between ICs uses protocols such as CAN and SPI. The basic period used in these communications is based on the oscillation period of the crystal unit. ing. For example, quartz resonators having a frequency of ± 0.3% or less are generally commercially available for CAN use.

  Further, as C1, for example, a capacitor element incorporated in an integrated circuit can be used. The capacitance element has a temperature dependence coefficient that is one digit or more lower than that of a resistance element incorporated in an integrated circuit. For example, the capacitance element has an accuracy of about ± 0.3% in the range of -40 ° C to 175 ° C. can get.

  Here, assuming that the minimum adjustable unit of the reference current I1 is designed in increments of 0.1%, for example, in this example, the reference current I1 having an accuracy of about ± 0.7% can be obtained with the reference voltage V1 as a reference.

  In this embodiment, a method for adjusting the current of the reference current source 100 will be described.

  FIG. 5 shows an example of the configuration of the current source correction circuit 1 for switching the current of the reference current source 100.

  The reference current source 100 is configured so that the reference voltage source 101 for supplying the reference voltage V1, the variable resistor R10 for converting the reference voltage to the current I10, and the voltage V2 applied to the resistor R10 are made equal to the reference voltage V1. The error amplifier 102 and the NMOS 104, and the current mirror circuit 105 for distributing the current I10 flowing through the resistor 103 to the oscillation circuit and other analog circuits.

  The variable resistor R10 is composed of, for example, a plurality of resistor elements connected in series or in parallel, and the resistance value can be switched stepwise by electrically switching the number of connected resistors by a MOS switch or the like. A circuit can be realized.

  The period comparator 300 compares T1 and T2 shown in the first embodiment. If T1 <T2, the resistance value of the variable resistor R10 is increased by one step from the current setting, and T1> T2. In contrast, a control signal for reducing the resistance value by one level is output.

  Since the current I10 has a relationship of I10 = V2 / R10, if R10 is increased, the reference current is decreased, and if R10 is decreased, the reference current is increased. Therefore, the effect described in the first embodiment can be obtained.

  In this embodiment, another example of the current adjustment method of the reference current source 100 will be described.

  FIG. 6 shows an example of the configuration of the current source correction circuit 1 for switching the current of the reference current source 100.

  The reference current source 100 includes a resistance element R20 for converting a reference voltage into a current I10, PMOS elements 601 to 603 constituting a current mirror circuit, 106 and 107, and of these, a part of the mirror source The PMOS elements 602 to 603 include switches SW61 to 62 that can be switched ON / OFF.

  The current mirror circuit has the current I10 as an input and outputs currents I1 and I4 as currents supplied to the oscillation circuit and various analog circuits, respectively. The input / output current ratio, that is, the mirror ratio at this time, is Among the PMOS elements 601 to 603 to be determined, the ratio is determined by a ratio between the total gate width of the ON elements and the gate widths of the PMOS elements 106 and 108 to be mirror destinations. Here, by applying a weight of, for example, 1: 2 to the gate width of the PMOS elements 602 and 603 that can be switched ON / OFF, four combinations of mirror ratios can be set depending on the ON / OFF combination of each switch. That is, the setting of the supply current of the reference current source can be set in four stages.

  The frequency comparator 300 compares T1 and T2 shown in the first embodiment. If T1 <T2, the supply current is increased by one step from the current setting. If T1> T2, the frequency comparator 300 reverses. The ON / OFF combination of the SWs 61 to 62 is changed so as to decrease the supply current by one step.

  Therefore, the effect described in the first embodiment can be obtained.

  In the present invention, the number of combinations of mirror ratios shown in this embodiment is not limited to this, and the number of elements and the combination can be changed depending on the required current accuracy. In this embodiment, the mirror source is variable, but the same effect can be obtained even if the mirror destination is variable.

  In this embodiment, a circuit configuration example that can extract a reference period from a communication signal will be described.

  FIG. 7 is obtained by adding a function of extracting a reference period from a communication signal and generating a comparison period for comparison with the reference period from an oscillation period to the configuration of the first embodiment.

  The current source correction circuit 1 determines a data length of a communication signal, sets a count number of oscillation periods and outputs a count reset signal, a reference period generation circuit 702 that generates a reference period from the communication signal, and , A period counter 703 that receives the setting signal from 701 and counts the oscillation period, and a comparison period generation circuit 704 that outputs the count period of the period counter.

  The other configurations in FIG. 7 have the same functions as the configurations denoted by the same reference numerals shown in FIG. 1 and will not be described.

  FIG. 8 is an example of a timing chart for explaining the operation of the present embodiment.

  The communication signal includes a recognition pattern S indicating the start of a communication frame, a pattern E indicating the end, data length information L to be transmitted, and data to be communicated, as represented by CAN communication, for example. Shall.

  The reference cycle generation circuit 702 extracts the period of the data of the communication signal itself and outputs it in the reference cycle T2.

  The data determination circuit 701 receives the information of the data length L and sets the count number of the period counter 703. The number of counts set here is set so that a desired Iref can be obtained when T1 = T2.

  When the count number is set, the period counter 703 counts the oscillation period T10 up to the set count number, and outputs the count period as the comparison period T1.

  The period comparator 300 compares the reference period T2 with T1 after the comparison period T1 is output, and controls the supply current value of the reference current source 100 as in the first embodiment.

  According to the present embodiment, as long as it is connected to a communication network that can obtain a desired cycle accuracy of T2, it is possible to reduce the number of components without having to prepare a dedicated element such as a crystal resonator.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment. The signal polarity shown in the timing chart is an example, and the present invention is not limited to this. In addition, each of the above-described configurations, functions, processing units, processing means, etc. may be realized by hardware, for example, by designing a part or all of them with a single integrated circuit, or with a plurality of integrated circuits. It may be realized.

DESCRIPTION OF SYMBOLS 1 Current source correction circuit 100 Period comparator 101 Band gap reference circuit 102 Error amplifier 103 Resistance element 104 NMOS
Reference Signs List 105 current mirror circuit 200 oscillation circuit 201 current mirror circuit 300 reference current source 701 data determination circuit 702 reference period generation circuit 703 period counter 704 comparison period generation circuit
A T1 = proportional coefficient with A / I1 relationship
C1 to C2 charge / discharge capacity of oscillation circuit
CMP1 non-inverting comparator
I10 Reference current generated by the voltage-current converter
I1 Reference current supplied to the oscillation circuit
I2 Oscillator charging current
I3 Oscillation circuit discharge current
I4 Reference current supplied to analog circuit
Iref desired current value
OPA1 operational amplifier
R1 to R2 Non-inverting amplifier feedback resistance
R10 variable resistor
R20 resistance element
Oscillation period for T1 period comparison
Reference period for T2 period comparison
V1 reference voltage
V2 Voltage applied to the resistance element of the voltage-current converter
V3 Oscillator circuit operating voltage
V4 Oscillator circuit comparator input voltage

Claims (5)

A reference current source that is built in the integrated circuit and outputs a reference current; and
An oscillation circuit that is driven by the current generated by the reference current source and can arbitrarily set the oscillation period;
A period comparator having an output period of the oscillation circuit as a first input and a reference period input from the outside of the integrated circuit as a second input;
The cycle comparator is a reference current source circuit that adjusts the reference current so that a difference between the first cycle and the second cycle is within a predetermined range. The reference current source includes a variable resistance element,
The reference current source circuit according to claim 1, wherein the reference current is adjusted by changing a resistance value of the variable resistance element. The reference current source includes a current mirror circuit;
The reference current source circuit according to claim 1, wherein the reference current is adjusted by changing a mirror ratio of the current mirror circuit.   The reference current source circuit according to claim 1, wherein the input of the reference period is extracted from a communication signal with the outside of the integrated circuit. In the reference current circuit that outputs the reference current I1,
A reference current source circuit that compares the internal clock T1 with the external clock T2 and adjusts I1 so that the difference between T1 and T2 falls within a predetermined range.

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