Calibration Circuit and Transmitter Including the Same

Abstract

The present application relates to a calibration circuit and a transmitter including the same. A calibration circuit includes: an oscillator configured to generate an oscillation signal according to a control voltage; a counter configured to generate a count value according to the oscillation signal; and a control circuit configured to control a pull-up driver and a pull-down driver commonly coupled to an output node according to the count value, wherein the control circuit compares a reference count value of the counter by providing a reference voltage as the control voltage for a unit control period with a count value of the counter by providing an output voltage of the output node as the control voltage for the unit control period, and controls a pull-up control signal for adjusting an on-resistance of the pull-up driver and a pull-down control signal for adjusting an on-resistance of the pull-down driver.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10 - 2020 - 0092086, filed on July 24, 2020, the entire content of which is incorporated herein by reference. Technical field

[0003] Each embodiment relates to a calibration circuit and a transmitter including the calibration circuit. More specifically, it relates to a calibration circuit including an oscillator and a transmitter including the calibration circuit. Background art

[0004] During the calibration operation, the output impedance of the transmitter is adjusted to be equal to the characteristic impedance.

[0005] Figure 1 A conventional transmitter 10 is shown.

[0006] The conventional transmitter 10 includes a pull - up driver 1 and a pull - down driver 2 commonly coupled to an output node No.

[0007] The output node No is coupled to the channel for transmitting a signal.

[0008] In Figure 1 , other elements in addition to the pull - up driver 1 and the pull - down driver 2 may be included in the calibration circuit.

[0009] The calibration circuit adjusts the pull - up impedance of the pull - up driver 1 and the pull - down impedance of the pull - down driver 2 to be equal to the characteristic impedance of the channel.

[0010] Referring to Figure 1 , the calibration circuit includes a replicated pull - up driver 3, whose configuration is substantially the same as that of the pull - up driver 1.

[0011] The replicated pull - up driver 3 is coupled to a reference resistor RZ through a replicated output node Nr, and the impedance of the reference resistor RZ is set to be equal to the characteristic impedance.

[0012] The on - impedance of the pull - up driver 1 and the replicated pull - up driver 3 is controlled according to the pull - up control signal PU, and the on - impedance of the pull - down driver 2 is controlled according to the pull - down control signal PD.

[0013] Techniques for controlling the on - impedance of drivers according to control signals are well - known to those skilled in the art. Therefore, a detailed description thereof is omitted herein.

[0014] The first counter 21 increases or decreases the pull-up control signal PU according to the first comparison signal CMP1, and the second counter 22 increases or decreases the pull-down control signal PD according to the second comparison signal CMP2.

[0015] The first comparator 31 compares the reference voltage VREF and the replicated output voltage VZQ, and outputs a first comparison signal CMP1 with a high or low level according to the comparison result.

[0016] At this time, the reference voltage generator 40 outputs a reference voltage VREF with a level of 1 / 2 of the power supply voltage.

[0017] The pull-up impedances of the pull-up driver 1 and the replicated pull-up driver 3 should be equal to the characteristic impedance, and in this case, the replicated output voltage VZQ is preferably equal to the level of 1 / 2 of the power supply voltage.

[0018] The second comparator 32 compares the reference voltage VREF and the output voltage VZQN, and outputs a second comparison signal CMP2 with a high or low level according to the comparison result.

[0019] After the calibration for the pull-up driver 1 is completed, the output impedance of the pull-up driver 1 becomes equal to the characteristic impedance.

[0020] The pull-down impedance of the pull-down driver 2 should be equal to the characteristic impedance, and in this case, the output voltage VZQN should have a level of 1 / 2 of the power supply voltage.

[0021] The first comparator 31 and the second comparator 32 output their comparison results synchronously with the first clock signal CLK1, and the first counter 21 and the second counter 22 update the pull-up control signal PU and the pull-down control signal PD synchronously with the second clock signal CLK2, and the phase of the second clock signal CLK2 is different from that of the first clock signal CLK1. The first counter 21 and the second counter 22 are reset in response to the reset control signal RESET.

[0022] As described above, the conventional calibration circuit uses the first comparator 31 and the second comparator 32 to perform the calibration operation. Due to the inherent offset or mismatch in the first comparator 31 and the second comparator 32, the pull-up control signal PU and the pull-down control signal PD cannot converge to the optimal values. Summary of the Invention

[0023] According to an embodiment of the present disclosure, a calibration circuit may include: an oscillator configured to generate an oscillation signal according to a control voltage; a counter configured to generate a count value by counting the frequency of the oscillation signal; and a control circuit configured to control a pull-up driver and a pull-down driver commonly coupled to an output node based on the count value, wherein the control circuit compares a reference count value of the counter with a first count value of the counter, and then determines a pull-up control signal, a pull-down control signal, or both based on the comparison result, the pull-up control signal adjusts the on-impedance of the pull-up driver and the pull-down control signal adjusts the on-impedance of the pull-down driver, the reference count value is determined by providing a reference voltage as the control voltage to the oscillator, and the first count value is determined by providing the output voltage of the output node as the control voltage to the oscillator.

[0024] According to an embodiment of the present disclosure, a transmitter may include: a pull-up driver and a pull-down driver commonly coupled to a channel at an output node; an oscillator configured to generate an oscillation signal according to a control voltage; a counter configured to generate a count value by counting the frequency of the oscillation signal; and a control circuit configured to control the pull-up driver and the pull-down driver based on the count value, wherein the control circuit compares a reference count value of the counter with a first count value of the counter, and then determines a pull-up control signal, a pull-down control signal, or both based on the comparison result, the pull-up control signal adjusts the on-impedance of the pull-up driver and the pull-down control signal adjusts the on-impedance of the pull-down driver, the reference count value is determined by providing a reference voltage as the control voltage to the oscillator, and the first count value is determined by providing the output voltage of the output node as the control voltage to the oscillator. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Like reference numerals throughout the drawings indicate like or functionally similar elements. The drawings, together with the following detailed description, are incorporated in and form a part of the specification, and the drawings are used to further illustrate embodiments including the inventive concepts claimed and to explain various principles and advantages of these embodiments.

[0026] Figure 1 is a block diagram showing a conventional transmitter.

[0027] Figure 2 is a block diagram showing a transmitter according to an embodiment of the present disclosure.

[0028] Figure 3 is a block diagram showing a transmitter according to another embodiment of the present disclosure.

[0029] Figure 4 and Figure 5 is a diagram showing a calibration operation according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0030] The following will describe each embodiment with reference to the accompanying drawings. The embodiments are provided for illustrative purposes, and other embodiments that are not explicitly shown or described are feasible. In addition, the embodiments of the present disclosure can be modified, which will be described in detail below.

[0031] Figure 2 A transmitter 1000 according to an embodiment of the present disclosure is shown.

[0032] The transmitter 1000 includes a pull-up driver 1 and a pull-down driver 2 commonly coupled to an output node No.

[0033] The output node No is coupled to a channel for transmitting a signal. The channel can be formed by a transmission line.

[0034] In Figure 2 In addition to the pull-up driver 1 and the pull-down driver 2, other elements can be included in the calibration circuit.

[0035] The calibration circuit adjusts the pull-up impedance of the pull-up driver 1 and the pull-down impedance of the pull-down driver 2 to be equal to the characteristic impedance of the channel. The calibration circuit includes a replicated pull-up driver 3, whose configuration is substantially the same as that of the pull-up driver 1.

[0036] The replicated pull-up driver 3 is coupled to a reference resistor RZ through a replicated output node Nr, and the impedance of the reference resistor RZ is set to be equal to the characteristic impedance of the channel.

[0037] The on-impedance of the pull-up driver 1 and the replicated pull-up driver 3 is controlled according to a pull-up control signal PU, and the on-impedance of the pull-down driver 2 is controlled according to a pull-down control signal PD.

[0038] In this embodiment, it is assumed that a power supply voltage is applied to the pull-up driver 1 and the replicated pull-up driver 3, and the pull-down driver 2 is grounded.

[0039] The circuit for controlling the on-impedance of the driver according to the control signal is well known to those of ordinary skill in the art, so its detailed description is omitted here.

[0040] A control circuit 100 controls the calibration operation and generates a pull-up control signal PU and a pull-down control signal PD.

[0041] The control circuit 100 generates a pull-up control signal PU and a pull-down control signal PD based on a count value CNT provided by a counter 200.

[0042] The counter 200 provides a count value CNT by performing a counting operation on an oscillation signal OSC provided by an oscillator 300. During the counting operation, the counter 200 counts the frequency of the oscillation signal OSC.

[0043] The oscillator 300 provides an oscillation signal OSC by performing an oscillation operation according to a control voltage VC.

[0044] During the calibration operation, one of a reference voltage VREF, a replica output voltage VZQ, and an output voltage VZQN is provided as the control voltage VC to the oscillator 300.

[0045] The reference voltage VREF is provided by a reference voltage generator 40.

[0046] The replica output voltage VZQ is a voltage output from the replica pull-up driver 3 through a replica output node Nr.

[0047] The output voltage VZQN is a voltage on an output node No to which the pull-up driver 1 and the pull-down driver 2 are commonly coupled.

[0048] The calibration circuit includes: a first switch 51 that provides the reference voltage VREF to the oscillator 300 in response to a reference voltage selection signal VRSEL; a second switch 52 that provides the replica output voltage VZQ in response to a pull-up selection signal PUSEL; and a third switch 53 that provides the output voltage VZQN to the oscillator 300 in response to a pull-down selection signal PDSEL.

[0049] Next, with reference to Figure 4 and Figure 5 the calibration operation of the control circuit 100 will be described.

[0050] In Figure 4 and Figure 5 the time period between Ti-1 and Ti (1 ≤ i ≤ m) corresponds to a unit control period that remains constant, and the control circuit 100 controls the calibration operation according to the unit control period.

[0051] The calibration operation includes a pull-up calibration operation for determining a pull-up control signal PU and a pull-down calibration operation for determining a pull-down control signal PD.

[0052] In Figure 2 the embodiment, after performing the pull-up calibration operation, the pull-down calibration operation is performed.

[0053] In the time period between T0 and T1, the control voltage VC is set to the reference voltage VREF, in the time period between T1 and Tn, the control voltage VC is set to the replica output voltage VZQ, and in the time period between Tn and Tm, the control voltage VC is set to the output voltage VZQN.

[0054] At T0, counter 200 starts a counting operation. Through the counting operation based on the reference voltage VREF, a reference count value is determined and stored, and the value of the pull-up control signal PU is initialized. After saving the reference count value, the count value CNT of counter 200 is reset, and the counting operation starts again at T1.

[0055] Subsequently, the count value CNT obtained from the counting operation is compared with the reference count value, and the value of the pull-up control signal PU is adjusted at T2 according to the comparison result.

[0056] In this embodiment, it is assumed that when the level of the control voltage VC increases, the frequency of the oscillation signal OSC output from the oscillator 300 increases.

[0057] In this case, if the count value CNT is greater than the reference count value, it means that the level of the replicated output voltage VZQ is higher than the reference voltage VREF, and thus the pull-up control signal PU is set in the direction to increase the on-impedance of the pull-up driver 1.

[0058] Conversely, if the count value CNT is less than the reference count value, it means that the level of the replicated output voltage VZQ is lower than the reference voltage VREF, and thus the pull-up control signal PU is set in the direction to reduce the on-impedance of the pull-up driver 1.

[0059] At each of T2 to Tn, the count value CNT is reset, the counting operation starts again, and the operations performed during the time period between T1 and T2 are repeated.

[0060] At Tn, the count value CNT is compared with the reference count value, and the value of the pull-up control signal PU is determined accordingly.

[0061] The conditions for determining the value of the pull-up control signal PU can be designed in various ways according to the exemplary embodiments. For example, if the difference between the reference count value and the count value CNT is less than a predetermined threshold, the value of the pull-up control signal PU can be determined.

[0062] After determining the value of the pull-up control signal PU, the pull-down calibration operation continues.

[0063] As Figure 5 shown, after initializing the value of the pull-down control signal PD at Tn, the count value CNT is reset and the counting operation starts.

[0064] At Tn + 1, the count value CNT is compared with the reference count value, and the value of the pull-down control signal PD is adjusted according to the comparison result.

[0065] If the count value CNT is greater than the reference count value, it means that the level of the output voltage VZQN is higher than the reference voltage VREF, and thus the pull - down control signal PD is set in the direction to reduce the on - resistance of the pull - down driver 2.

[0066] Conversely, if the count value CNT is less than the reference count value, it means that the level of the output voltage VZQN is lower than the reference voltage VREF, and thus the pull - down control signal PD is set in the direction to increase the on - resistance of the pull - down driver 2.

[0067] Thereafter, at each of Tn + 1 to Tm, the count value CNT is reset, the counting operation starts again, and the operations performed in the time period between Tn and Tn + 1 are repeated.

[0068] At Tm, the count value CNT is compared with the reference count value, and the value of the pull - down control signal PD is determined according to the comparison result.

[0069] The conditions for determining the value of the pull - down control signal PD can be designed in various ways according to the exemplary embodiments. For example, if the difference between the reference count value and the count value CNT is less than a predetermined threshold, the value of the pull - down control signal PD can be determined.

[0070] Figure 3 A transmitter 2000 according to another embodiment of the present disclosure is shown.

[0071] Unlike Figure 2 the embodiment of Figure 3 the embodiment includes a replicated pull - down driver 4 instead of a replicated pull - up driver 3.

[0072] In addition, the replicated output node Nr is coupled to the output terminal of the replicated pull - down driver 4, and the reference resistor RZ is coupled between the replicated output node Nr and the power supply voltage VDD.

[0073] In Figure 3 the embodiment, first, a pull - down calibration operation is performed using the replicated pull - down driver 4, and then a pull - up calibration operation is performed using the pull - up driver 1.

[0074] In addition, the second switch 52 provides the output voltage VZQN to the oscillator 300 in response to the pull - up selection signal PUSEL, and the third switch 53 provides the replicated output voltage VZQ to the oscillator 300 in response to the pull - down selection signal PDSEL.

[0075] When the reference voltage VREF is supplied to the oscillator 300, a reference count value is set by counting the frequency of the oscillation signal OSC output from the oscillator 300. Thereafter, the value of the pull-down control signal PD is determined by performing a pull-down calibration operation based on the replicated output voltage VZQ supplied to the oscillator 300. Subsequently, the value of the pull-up control signal PU is determined by performing a pull-up calibration operation based on the output voltage VZQN supplied to the oscillator 300. These operations are similar to the operations described with reference to Figure 4 and Figure 5 described.

[0076] Therefore, according to the embodiments described above with reference to Figure 2 the functions and calibration operations of the control circuit 100, the counter 200, the oscillator 300, and the reference voltage generator 40 in Figure 3 are easily understood, and thus their detailed descriptions will be omitted.

[0077] Although the embodiments have been described for illustrative purposes, various changes and modifications are possible.

Claims

1. A calibration circuit, comprising: An oscillator configured to generate an oscillation signal according to a control voltage; A counter configured to generate a count value by counting the frequency of the oscillation signal; And A control circuit configured to control a pull-up driver and a pull-down driver commonly coupled to an output node based on the count value, Wherein the control circuit compares a reference count value of the counter with a first count value of the counter, and then determines a pull-up control signal or a pull-down control signal based on the comparison result, the pull-up control signal adjusts the on-impedance of the pull-up driver and the pull-down control signal adjusts the on-impedance of the pull-down driver, the reference count value is determined by providing a reference voltage to the oscillator as the control voltage, and the first count value is determined by providing the output voltage of the output node to the oscillator as the control voltage.

2. The calibration circuit according to claim 1, further comprising: A replicated pull-up driver that replicates the pull-up driver; And A reference resistor coupled to a replicated output node of the replicated pull-up driver, Wherein the control circuit uses the pull-up control signal to control the on-impedance of the replicated pull-up driver.

3. The calibration circuit according to claim 2, wherein, The control circuit compares the reference count value with a second count value of the counter determined by providing the replicated output voltage of the replicated output node as the control voltage, and then determines the pull-up control signal based on the comparison result.

4. The calibration circuit according to claim 3, wherein, The control circuit determines the pull-down control signal after the pull-up control signal is determined.

5. The calibration circuit according to claim 3, wherein, The control circuit determines the pull-up control signal when the difference between the reference count value and the second count value is less than a first predetermined threshold value, and determines the pull-down control signal when the difference between the reference count value and the first count value is less than a second predetermined threshold value.

6. The calibration circuit according to claim 1, further comprising: A replicated pull-down driver that replicates the pull-down driver; And A reference resistor coupled to a replicated output node of the replicated pull-down driver, Wherein the control circuit uses the pull-down control signal to control the on-impedance of the replicated pull-down driver.

7. The calibration circuit according to claim 6, wherein, The control circuit compares the reference count value with a second count value of the counter determined by providing the replicated output voltage of the replicated output node as the control voltage, and then determines the pull-down control signal based on the comparison result.

8. The calibration circuit according to claim 7, wherein, The control circuit determines the pull-up control signal after the pull-down control signal is determined.

9. The calibration circuit according to claim 7, wherein, The control circuit determines the pull-down control signal when the difference between the reference count value and the second count value is less than a first predetermined threshold value, and determines the pull-up control signal when the difference between the reference count value and the first count value is less than a second predetermined threshold value.

10. A transmitter, comprising: A pull-up driver and a pull-down driver commonly coupled to a channel at an output node: An oscillator configured to generate an oscillation signal according to a control voltage; A counter configured to generate a count value by counting the frequency of the oscillation signal; And A control circuit configured to control the pull-up driver and the pull-down driver based on the count value. The control circuit compares a reference count value of the counter with a first count value of the counter, and then determines a pull-up control signal or a pull-down control signal based on the comparison result. The pull-up control signal adjusts the on-resistance of the pull-up driver and the pull-down control signal adjusts the on-resistance of the pull-down driver. The reference count value is determined by providing a reference voltage to the oscillator as the control voltage, and the first count value is determined by providing the output voltage of the output node to the oscillator as the control voltage.

11. The transmitter according to claim 10, further comprising: A replicated pull-up driver that replicates the pull-up driver; And A reference resistor coupled to a replicated output node of the replicated pull-up driver, wherein the control circuit uses the pull-up control signal to control the on-resistance of the replicated pull-up driver.

12. The transmitter according to claim 11, wherein, The control circuit compares the reference count value with a second count value of the counter determined by providing the replicated output voltage of the replicated output node as the control voltage, and then determines the pull-up control signal based on the comparison result.

13. The transmitter according to claim 12, wherein, The control circuit determines the pull-down control signal after the pull-up control signal is determined.

14. The transmitter according to claim 12, wherein, The control circuit determines the pull-up control signal when the difference between the reference count value and the second count value is less than a first predetermined threshold value, and determines the pull-down control signal when the difference between the reference count value and the first count value is less than a second predetermined threshold value.

15. The transmitter according to claim 10, further comprising: A replicated pull-down driver that replicates the pull-down driver; And A reference resistor coupled to a replicated output node of the replicated pull-down driver, wherein the control circuit uses the pull-down control signal to control the on-resistance of the replicated pull-down driver.

16. The transmitter according to claim 15, wherein, The control circuit compares the reference count value with a second count value of the counter determined by providing the replicated output voltage of the replicated output node as the control voltage, and then determines the pull-down control signal based on the comparison result.

17. The transmitter according to claim 16, wherein, The control circuit determines the pull-up control signal after the pull-down control signal is determined.

18. The transmitter according to claim 16, wherein, The control circuit determines the pull-down control signal when the difference between the reference count value and the second count value is less than a first predetermined threshold value, and determines the pull-up control signal when the difference between the reference count value and the first count value is less than a second predetermined threshold value.

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