CN101330284A - Time constant correction device and related method thereof - Google Patents

Abstract

The invention discloses a time constant correction device, which comprises: a first voltage generating circuit for generating a first voltage by using a first current flowing through a capacitor element; a second voltage generating circuit for generating a second voltage by passing a second current through an impedance element; and a comparison circuit for comparing the first voltage with the second voltage to generate a comparison signal, wherein the first voltage generation circuit is provided with an analog adjustment element for adjusting the first voltage according to the comparison signal until the first voltage is equal to the second voltage so that a time constant corresponding to an equivalent capacitance value corresponding to the first current flowing through the capacitance element and an equivalent impedance value corresponding to the second current flowing through the impedance element reaches a predetermined value.

Description

Time constant correction device and related method

technical field

The invention relates to a time constant calibration circuit, in particular to a time constant calibration circuit and a related method which uses an analog adjustment mechanism to adjust a capacitance or a current source.

Background technique

Filters are required in many communication transmission application circuits. Among them, the resistance capacitor filter (R.C. filter) is easier to control in design because of its variability than the active filter (gmC filter), so it is widely used in various fields. However, there are often variations in the process of resistor-capacitor components, which makes the actual value of the resistor-capacitor time constant (RC time constant) different from the design value, which in turn affects the performance of the circuit and the accuracy of the frequency response. Without correction, the difference between the actual value of the resistor-capacitor time constant and the design value can even be as high as ±30% to 50% (depending on the type of capacitor and resistor used); relatively, the frequency response of the circuit is also There will be an excursion of such a surprising magnitude that it will be very detrimental to circuits that require accurate frequency response.

Aiming at the time constant error of resistors and capacitors caused by process variation, many circuits and methods for automatic frequency adjustment have been developed. Please refer to FIG. 1 , which is a circuit structure diagram of a conventional time constant correction device 100 . As shown in FIG. 1 , the time constant calibration device 100 includes a first voltage generating circuit 110 , a second voltage generating circuit 120 and a comparing circuit 130 . The first voltage generating circuit 110 includes a clock signal generator 112 , a fixed current source 114 (used to provide a certain current I _c ), and a switched capacitor circuit 140 . The switched capacitor circuit 140 includes a first capacitive element C1 (which is a variable capacitive element), a first switch element 142 , a second switch element 143 , a second capacitive element Cs1 and a third switch element 145 . The clock signal generator 112 generates a first clock signal ψ ₁ and a second clock signal ψ ₂ respectively, wherein the first clock signal ψ ₁ and the second clock signal ψ ₂ are non-overlapped clocks , used to drive the switched capacitor circuit 140 to generate the first voltage Vc. The second voltage generating circuit 120 includes a differential circuit 122, a fixed current source 123 (used to provide a certain current Ic), a transistor 124 and another fixed current source 125 (used to provide a certain current K*Ic flowing through an impedance Element R1 is used to generate a second voltage Vr. The comparison circuit 130 includes a comparator 132 and a digital logic 134, wherein the comparator 132 compares the second voltage Vr and the bandgap reference voltage Vref to generate a comparison signal and send it to The digital logic 134 turns on or off each unit capacitance to generate a digital handle, and then adjusts the final capacitance value of the capacitor C1. Please note that the prior art must have a bandgap reference voltage circuit (bandgap reference voltage circuit) to generate the required However, since the bandgap reference voltage circuit has been widely used in various applications to provide a stable reference voltage in a temperature range, its operation and function are well known in the art are well known, so I will not repeat them here.

Please note that the purpose of the existing time constant correction device 100 is to maintain a fixed time constant R1×C1 by adjusting the variable capacitor C1. In simple terms, two mathematical identities are used in this circuit. First, from the second voltage From the point of view of the circuit 120, the reference voltage Vr is: Vr=K×Ic×R1, comparing the reference voltage _Vr with the bandgap reference voltage Vref, Vref=K×Ic×R1 can be obtained in a steady state, then, From the point of view of the first voltage circuit 110, the clock signal generator 112 generates the first clock signal ψ ₁ and the second clock signal ψ ₂ , and the first clock signal ψ ₁ and the second clock signal ψ ₂ do not overlap with each other. The repeated clock (its cycle is T) is used to drive the switched capacitor circuit 140 to generate the first voltage Vc, so when the current Ic charges the capacitor C1 within one cycle, the first voltage Vc generated on the capacitor C1 is: Vc=Ic×T/(2×C1), when the clock discharges the capacitor C1, the capacitor Cs1 will maintain the voltage Vc, and when Vc=Vref, R1×C1=T/2K, since T and K are known constant, so the time constant is a fixed value, the control method of this circuit is to use the comparator 132 to generate a digital handle to turn on or off each unit of capacitance and then adjust the size of the final capacitance value, however, this method uses a digital handle to adjust the capacitance Value circuit, if the resolution is good, it is necessary to design quite a lot of unit capacitance branches with switches, so it is not suitable for the application of capacitance amplification technology.

However, system-on-chip (SoC) has become the mainstream of integrated circuit design, and PLL or PLL-based applications are indispensable for SoC. Those skilled in the art should be able to easily understand that when the CMOS process advances, the area of the transistor will also shrink, but the passive components in the chip are not included. The low-pass filter is a part of the phase-locked loop. It is composed of resistors and capacitors. In the past few years, the low-pass filter was always designed outside the chip to reduce the chip area and save production costs. Today, the low-pass filter will be The integration of low-pass filters into the chip is more in line with the trend of SoC. However, these passive components still occupy most of the chip area, so how to reduce the area of these passive components has become a very important problem in circuit design. important subject.

Contents of the invention

A main objective of the present invention is to provide a time constant calibration device and related method to solve the above problems. In one embodiment of the present invention, a time constant correction device is disclosed, which includes: a first voltage generating circuit, which uses a first current to flow through a capacitive element to generate a first voltage; a second voltage generating circuit , which uses a second current to flow through an impedance element to generate a second voltage; and a comparison circuit for comparing the first voltage and the second voltage to generate a comparison signal, wherein the first voltage generation circuit An analog adjustment element is provided for adjusting the first voltage according to the comparison signal until the first voltage is equal to the second voltage so that the first current flows through the capacitance element corresponding to an equivalent capacitance value corresponding to the first voltage A time constant corresponding to an equivalent impedance value corresponding to the two currents flowing through the impedance element reaches a predetermined value.

The present invention also discloses a time constant correction method, which includes: providing a first current and a capacitive element; using the first current to flow through the capacitive element to generate a first voltage; providing a second current and a set of an impedance element; use the second current to flow through the impedance element to generate a second voltage; and compare the first voltage and the second voltage to generate a comparison signal, and adjust through an analog adjustment method according to the comparison signal The first voltage, until the first voltage is equal to the second voltage so that an equivalent capacitance value corresponding to the first current flowing through the capacitive element and an equivalent capacitance value corresponding to the second current flowing through the impedance element A time constant corresponding to the impedance value reaches a predetermined value.

Description of drawings

Fig. 1 is a circuit structure diagram of a conventional time constant correction device.

Fig. 2 is a simple functional block diagram of the time constant correction device of the present invention.

FIG. 3 is a circuit structure diagram of the time constant correction device according to the first embodiment of the present invention.

FIG. 4 is a circuit structure diagram of a time constant correction device according to a second embodiment of the present invention.

FIG. 5 is a generalized flowchart of the time constant correction method of the present invention.

Description of reference symbols

100, 200, 300, 400 Time constant correction device 110, 210, 310, 410 The first voltage generating circuit 212 ANALOG ADJUSTMENT COMPONENTS 120, 220, 320, 420 The second voltage generation circuit 130, 230, 330, 430 comparison circuit 112, 312, 412 clock signal generator 114, 125, 314 Fixed current source

142, 342, 442 The first switching element 143, 343, 443 The second switching element 145, 345, 445 The third switching element 122 Differential circuit 124 Transistor 132 Comparators 134 mathematical logic 140, 340, 440 Switched Capacitor Circuit 341, 441 The first capacitive element 344, 444 Second capacitive element 414 Voltage controlled current source

Detailed ways

Certain terms are used in the specification and subsequent claims to refer to particular elements. Those of ordinary skill in the art will appreciate that manufacturers may refer to the same element by different terms. This description and subsequent patent applications do not use the difference in name as a way to distinguish components, but use the difference in function of components as a criterion for distinguishing. The "comprising" mentioned throughout the specification and subsequent claims is an open-ended term, so it should be interpreted as "including but not limited to". Otherwise, the term "coupled" includes any direct and indirect means of electrical connection. Therefore, if it is described that a first device is coupled to a second device, it means that the first device may be directly electrically connected to the second device, or indirectly electrically connected to the second device through other devices or connection means.

Please refer to FIG. 2 , which is a simple functional block diagram of a time constant correction device 200 of the present invention. As shown in FIG. 2 , the time constant calibration device 200 includes a first voltage generating circuit 210 , a second voltage generating circuit 220 and a comparing circuit 230 . The first voltage generating circuit 210 uses a first current I ₁ to flow through a capacitive element to generate a first voltage V ₁ , and the second voltage generating circuit 220 uses a second current I ₂ (for example, I ₂ =K× I ₁ ) flows through an impedance element to generate a second voltage V ₂ , in addition, the comparison circuit 230 is electrically connected to the first voltage generation circuit 210 and the second voltage generation circuit 220, and is used to compare the first voltage V ₁ and the second voltage generation circuit. voltage V ₂ to generate a comparison signal V _adj , wherein the first voltage generating circuit 210 is provided with an analog adjustment element 212 for adjusting the first voltage V ₁ according to the comparison signal V _adj until the first voltage V ₁ is equal to the second The voltage V ₂ causes the first current I ₁ to flow through the capacitive element corresponding to an equivalent capacitance value (such as C1) and the second current I ₂ to flow through the impedance element corresponding to an equivalent impedance value (such as R1) A corresponding time constant reaches a predetermined value (for example, R1×C1=T/2K).

Please refer to FIG. 3 . FIG. 3 is a circuit structure diagram of a time constant correction device 300 according to a first embodiment of the present invention. As shown in FIG. 3 , the time constant calibration device 300 includes a first voltage generation circuit 310 , a second voltage generation circuit 320 and a comparison circuit 330 . The second voltage generation circuit 320 utilizes a fixed current source 322 to provide a second current I ₂ (in this embodiment, I ₂ =K×I ₁ )) to flow through an impedance element R ₁ (such as a resistor) to generate a The second voltage V _r , in addition, the first voltage generating circuit 310 includes a clock signal generator 312 , a fixed current source 314 and a switched capacitor circuit 340 . The clock signal generator 312 is used to generate a first clock signal ψ1 and a second clock signal ψ2, wherein the first clock signal ψ1 and the second clock signal ψ2 do not overlap with each other, and the period of the two is T; fixed One end of the current source 314 is coupled to a first voltage level (V _dd ); the switched capacitor circuit 340 includes a first capacitor element 341 , a first switch element 342 , a second switch element 343 , a second capacitor element 344 and The third switching element 345, wherein, the first end of the first capacitive element 341 is coupled to the current source 314, and the second end is coupled to a second voltage level (ground end), which is used for according to the current source 314 The provided first current I ₁ is charged to generate a first voltage V ₁ , wherein the first capacitive element 341 is an analog variable capacitor as the aforementioned analog adjustment element, as shown in FIG. 3 , the first capacitive element 341 (analog variable capacitor) is coupled to the comparison circuit 330, and is used to adjust its capacitance value according to a comparison signal V _adj ; the first switch element 342, its first end is coupled to the second voltage level, and its second terminal is coupled to the first end of the first capacitive element 341, and is used for selectively coupling the second end of the first switching element 342 to the first end of the first capacitive element 341 according to the second clock signal ψ ₂ , so that the first capacitive element 341 is discharged; the second switch element 343, a first end of which is coupled to the first end of the first capacitive element ₃₄₁ , is used to selectively allow the second The first end of the switch element 343 is coupled to the first end of the first capacitive element 341; the second capacitive element 344 has a first end coupled to the second end of the second switch element 343, and a second end of the second capacitive element 344 coupled to the second voltage level; and a third switching element 345, the first end of which is coupled to the first end of the second capacitive element 344, and the second end thereof is coupled to the comparison circuit 330 for use according to the first Two clock signals ψ2 selectively allow the second end of the third switching element 345 to be coupled to the first end of the second capacitive element 344; the comparison circuit 330 is electrically connected to the first voltage generation circuit 310 and the second voltage generation circuit 320 , used to compare the first voltage V ₁ and the second voltage V ₂ to generate the above comparison signal V _adj . The time constant correction device 300 adjusts the capacitance value of the first capacitive element 341 according to the comparison signal V _adj (that is, since the first voltage V ₁ =I _c ×T/(2×N×C _a ), it can be adjusted by adjusting N to achieve the purpose of adjusting the first voltage), until the first voltage _V1 is equal to the second voltage _V2 so that the first current _I1 flows through the equivalent capacitance value corresponding to the first capacitive element 341 and the second current _I2 flows A time constant corresponding to the equivalent impedance value corresponding to the impedance element R ₁ reaches a predetermined value (R ₁ ×C ₁ =T/2K).

Please note that the analog variable capacitor (i.e. the first capacitive element 341) includes a predetermined capacitance with a first capacitance C _a , and a capacitance amplification technique is applied to make the capacitance of the analog variable capacitor correspondingly greater than A second capacitance value N×C _a (N is greater than 1) of the first capacitance value C _a . In this embodiment, a capacitance amplification technique is used to adjust the first capacitance element 341. This capacitance amplification technique can reduce the small capacitance The capacitance value Ca that has is amplified by N times to obtain the desired capacitance value of the first capacitance element 341, under the same capacitance value _C1 , as the N value is larger, the capacitance area is smaller (that is, the required first The smaller the capacitance value C _a ), for example, if N can be designed to be 10, so the capacitance area can be reduced by 10 times, please note that since the capacitance value of the first capacitance element 341 must be properly adjusted to compensate the impedance element R ₁ and its own process variation, so the variable range of the N value must cover the process variation of the impedance element R ₁ and the first capacitive element 341 .

Please refer to FIG. 4 , which is a circuit structure diagram of a time constant correction device 400 according to a second embodiment of the present invention. As shown in FIG. 4 , the time constant calibration device 400 includes a first voltage generation circuit 410 , a second voltage generation circuit 420 and a comparison circuit 430 . The second voltage generating circuit 420 uses a second current I ₂ (I ₂ =K×I _c ) to flow through an impedance element R ₁ to generate a second voltage V _r ; and the first voltage generating circuit 410 includes a clock signal generating device 412 , voltage-controlled current source 414 and switched capacitor circuit 440 . The clock signal generator 412 is used to generate a first clock signal ψ ₁ and a second clock signal ψ ₂ , wherein the first clock signal ψ ₁ and the second clock signal ψ ₂ do not overlap with each other, and the periods of the two are T; a voltage-controlled current source 414, one end of which is coupled to a first voltage level (V _dd ), wherein the voltage-controlled current source 414 is used as the above-mentioned analog adjustment element and is coupled to the comparison circuit 430 for comparison based on The signal V _adj adjusts the first current I ₁ output by the voltage-controlled current source 414 (I ₁ =I _c /N); the switched capacitor circuit 440 includes a first capacitor element 441 (the capacitance value of which is the above-mentioned C _a , also That is, the first capacitive element 441 is implemented with a small capacitor), the first switch element 442 , the second switch element 443 , the second capacitive element 444 and the third switch element 445 . The first capacitive element 441, its first end is coupled to the voltage-controlled current source 414, and its second end is then coupled to a second voltage level (ground end), used for according to the output of the voltage-controlled current source 414 The first current I ₁ is charged to generate the first voltage V ₁ ; the first switch element 442 has a first end coupled to the second voltage level, and a second end coupled to the first capacitive element 441 . One end is used to selectively couple the second end of the first switching element 442 to the first end of the first capacitive element 441 according to the second clock signal ψ ₂ to discharge the first capacitive element 441; The switch element 443, the first end of which is coupled to the first end of the first capacitive element 441 is used for selectively coupling the first end of the second switch element 443 to the first capacitive element according to the first clock signal ψ1 The first end of 441; The second capacitive element 444, its first end is coupled to the second end of the second switching element 443, and its second end is then coupled to the second voltage level; and the third switching element 445, the first end of which is coupled to the first end of the second capacitive element 444, and the second end thereof is coupled to the comparison circuit 430, for selectively making the third switching element 445 according to the second clock signal ψ ₂ The second end of the second end is coupled to the first end of the second capacitive element 444; the comparison circuit 430 is electrically connected to the first voltage generation circuit 410 and the second voltage generation circuit 420, and is used to compare the first voltage _V1 and the second voltage V _r to generate a comparison signal V _aj , and adjust the first current I ₁ output by the voltage-controlled current source 414 according to the comparison signal V _adj (that is, because the first voltage V ₁ =(I _c /N)×T/(2 ×C _a ), so the purpose of adjusting the first voltage V ₁ can be achieved by adjusting N), until the first voltage V ₁ is equal to the second voltage V ₂ and the first current I ₁ flows through the first capacitive element 441 A time constant corresponding to the equivalent capacitance value and the equivalent impedance value corresponding to the second current I ₂ flowing through the impedance element R ₁ reaches a predetermined value (R ₁ ×C ₁ =T/2K).

In summary, the first embodiment of the present invention is to fix the current provided by a current source and use a capacitance amplification technique to adjust the capacitance value of the variable capacitor by comparing the signal V _adj in an analog manner to calibrate the time constant. However, It is not suitable to directly adjust the capacitance value on some specific application circuits, so the second embodiment of the present invention is to fix the capacitance value of a capacitor and use the comparison signal V _adj to adjust the output current of the voltage-controlled current source to achieve the same calibration The effect of the time constant. Please note that if the technical features of the above two embodiments are combined (that is, the voltage-controlled current source and the variable capacitor are used together), the purpose of correcting the time constant can also be achieved through appropriate control, which also belongs to the scope of the present invention.

Please refer to FIG. 5 , which is a generalized flowchart of the time constant calibration method of the present invention. Note that the flow shown in Figure 5 does not necessarily follow the order in which the steps are performed as shown, assuming that roughly the same results can be achieved. According to the above-mentioned embodiment, the operation of the time constant correction method of the present invention can be simply summarized as follows:

Step 500: The calibration procedure starts.

Step 502: Provide a first current and a capacitive element.

Step 504: Provide a second current and a set of resistive elements.

Step 506 : Use the first current to flow through the capacitive element to generate a first voltage.

Step 508 : Use the second current to flow through the impedance element to generate a second voltage.

Step 510: Compare the first voltage and the second voltage to generate a comparison signal.

Step 512: Does the comparison signal indicate that the first voltage is equal to the second voltage? If yes, go to step 516; otherwise, go to step 514.

Step 514 : Adjust the first voltage according to the comparison signal through an analog adjustment mechanism (for example, adjust the capacitive element implemented by a variable capacitor or adjust a voltage-controlled current source for providing the first current). Next, return to step 510 .

Step 516: The calibration process ends (a time constant corresponding to an equivalent capacitance value corresponding to the first current flowing through the capacitive element and an equivalent impedance value corresponding to the second current flowing through the impedance element reaches a predetermined value).

Compared with the prior art, the present invention not only saves circuit area and power consumption, but also does not require a bandgap reference voltage circuit to generate a bandgap reference voltage V _ref , and because a bandgap reference voltage circuit is not required, the The circuit design can be simplified and more flexible. In addition, the present invention uses an analog voltage control signal to cooperate with an analog-controlled variable capacitor, combined with capacitance amplification technology, thereby greatly saving the chip area occupied by the capacitor.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (7)

1. A time constant correction device comprising: a first voltage generating circuit, which uses a first current to flow through a first capacitive element to generate a first voltage; a second voltage generation circuit, which uses a second current to flow through an impedance element to generate a second voltage; and A comparison circuit, electrically connected to the first voltage generation circuit and the second voltage generation circuit, used to compare the first voltage and the second voltage to generate a comparison signal, wherein the first voltage generation circuit is provided with an analog an adjustment element, used to adjust the first voltage according to the comparison signal until the first voltage is equal to the second voltage so that the first current flows through an equivalent impedance value corresponding to the first capacitive element and the second A time constant corresponding to an equivalent impedance value corresponding to the current flowing through the impedance element reaches a predetermined value. 2. The device according to claim 1, wherein the first voltage generating circuit comprises: A clock signal generator, used to generate a first clock signal and a second clock signal, the first clock signal and the second clock signal do not overlap each other; a fixed current source, one end of which is coupled to a first voltage level for providing the first current; The first capacitive element has a first terminal coupled to the current source and a second terminal coupled to a second voltage level for charging according to the first current to generate the first voltage, wherein , the first capacitive element is an analog variable capacitor as the analog adjustment element, the analog variable capacitor is coupled to the comparison circuit, and is used to adjust the capacitance value of the analog variable capacitor according to the comparison signal; A first switching element, a first end of which is coupled to the second voltage level, and a second end of which is coupled to the first end of the first capacitive element, for selecting according to the second clock signal selectively coupling the first end of the first switch element to the first end of the first capacitive element to discharge the first capacitive element; a second switch element, a first end of which is coupled to the first end of the first capacitive element, and is used for selectively coupling a second end of the second switch element according to the first clock signal at the first end of the first capacitive element; a second capacitive element, a first end of which is coupled to the second end of the second switching element, and a second end of which is coupled to the second voltage level; and A third switching element, one of its first terminals is coupled to the first terminal of the second capacitive element, and its second terminal is coupled to the comparison circuit for selectively allowing The second end of the third switch element is coupled to the first end of the second capacitive element. 3. The device as claimed in claim 2, wherein the analog variable capacitor comprises a predetermined capacitance with a first capacitance value, and a capacitance amplification technique is applied to make the capacitance value of the analog variable capacitor correspondingly greater than A second capacitance value of the first capacitance value. 4. The device as claimed in claim 1, wherein the first voltage generating circuit comprises: A clock signal generator, used to generate a first clock signal and a second clock signal, the first clock signal and the second clock signal do not overlap each other; A voltage-controlled current source, one end of which is coupled to a first voltage level, is used to provide the first current, wherein, the voltage-controlled current source is used as the analog adjustment element and is coupled to the comparison circuit, and is used according to the comparison signal adjusts the first current; The first capacitive element has a first terminal coupled to the voltage-controlled current source, and a second terminal coupled to a second voltage level for charging according to the current source to generate the first voltage; A first switching element, a first end of which is coupled to the second voltage level, and a second end of which is coupled to the first end of the first capacitive element, for selecting according to the second clock signal selectively coupling the first end of the first switch element to the first end of the first capacitive element to discharge the first capacitive element; a second switch element, a first end of which is coupled to the first end of the first capacitive element, and is used for selectively coupling a second end of the second switch element according to the first clock signal at the first end of the first capacitive element; a second capacitive element, a first end of which is coupled to the second end of the second switching element, and a second end of which is coupled to the second voltage level; and A third switching element, one of its first terminals is coupled to the first terminal of the second capacitive element, and its second terminal is coupled to the comparison circuit for selectively allowing The second end of the third switch element is coupled to the first end of the second capacitive element. 5. A time constant correction method comprising: providing a first current and a capacitive element; using the first current to flow through the capacitive element to generate a first voltage; providing a second current and a set of resistive elements; using the second current to flow through the impedance element to generate a second voltage; and Comparing the first voltage and the second voltage to generate a comparison signal, and adjusting the first voltage through an analog adjustment method according to the comparison signal until the first voltage is equal to the second voltage so that the first current Until a time constant corresponding to an equivalent capacitance corresponding to the capacitance element flowing through the capacitance element and an equivalent impedance value corresponding to the second current flowing through the impedance element reaches a predetermined value. 6. The method of claim 5, wherein the capacitive element is an analog variable capacitor comprising a predetermined capacitance having a first capacitance value, and a capacitance amplification technique is applied to make the analog variable capacitor The capacitance of the capacitor corresponds to a second capacitance greater than the first capacitance, and the analog adjustment method adjusts the second capacitance corresponding to the analog variable capacitor according to the comparison signal to adjust the first voltage. 7. The method as claimed in claim 5, wherein the analog adjustment method adjusts the first current provided by a voltage-controlled current source according to the comparison signal to adjust the first voltage.

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