A high-precision current-calibrated RC oscillator

Abstract

The present application relates to a high-precision current-calibrated RC oscillator, including a segmented current calibration module, an operational amplifier module, a reference resistor, and a closed-loop feedback module. The segmented current calibration module is used to output a trimmed current and a fixed current according to an input external input current and a trim code; the fixed current generates a positive input voltage at the positive input end of the operational amplifier module, and the trimmed current and the reference resistor generate a negative input voltage at the negative input end of the operational amplifier module. The operational amplifier module is used to amplify, filter and oscillate the positive input voltage and the negative input voltage, and output a clock signal. The closed-loop feedback module is used to adaptively adjust the magnitude of the positive input voltage according to the frequency of the clock signal, so that the frequency of the clock signal reaches the target frequency. The present application is used to trim and calibrate the output clock of the RC oscillator, increase the current calibration monotonicity of the RC oscillator, reduce output glitches, and improve the output clock accuracy.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and in particular to a high-precision current-calibrated RC oscillator. Background Art

[0002] In a mixed digital-analog system, the clock reference source is an indispensable module that provides a clock signal. All digital signal processing processes must be carried out under the synchronization of the clock signal. Therefore, the stability and accuracy of the clock signal largely determine the performance of the entire circuit system. In the widely used clock reference circuit structure, the RC oscillator controls the current to charge and discharge the capacitor to achieve the output of a periodic clock signal. It has low power consumption, small area, and high integration, and has become the preferred structure for on-chip clock reference sources in the industry.

[0003] Two important indicators for measuring the accuracy of an RC oscillator are the temperature change rate and voltage linearity of the clock signal frequency it outputs. These two indicators describe how the clock frequency changes with temperature and power supply voltage, respectively. The smaller the temperature change rate and voltage linearity, the higher the accuracy of the RC oscillator.

[0004] One implementation of a traditional RC oscillator is as follows Figure 1 As shown in FIG. 1 , it is composed of a charging current source module, a reference voltage generation module, a switch capacitor module, a comparator module and an RS trigger module. Assume that the RS trigger Q terminal output φ m is low level, φ m The control switch S1 is closed, and the charging current Ic charges the capacitor C1, and the voltage V1 across the capacitor C1 rises. When V1 rises to Vf, the comparator output flips, the S input of the RS trigger is high, the RS trigger is set, and the Q output φ m Flip to high level, switch S1 opens, capacitor C1 discharges, V1 drops, and Q' outputs φ n The voltage V2 of capacitor C2 rises, and the output of the comparator flips after V2 rises to Vf. The R input of the RS trigger is high, the RS trigger is reset, and the Q output is low. The RC oscillator completes one cycle. The output frequency formula of the traditional RC oscillator can be derived from the above process. Usually, C1 and C2 are exactly the same, and Ic and Ir are equal in size, so the period T is equal to twice the time it takes for a single capacitor to charge to Vf, so the frequency is: f=Ic / 2CVf.

[0005] It can be seen from the above formula that the output clock frequency of the traditional RC oscillator is related to the size of the capacitor C, the reference voltage Vf, and the charging current Ic, where the size of the reference voltage Vf is related to the reference resistor Rf. In the integrated circuit manufacturing process, the size of the resistor and capacitor is not an ideal fixed value, but will change due to other external factors such as process angle, temperature and voltage. This change will lead to an increase in the temperature change rate and voltage linearity, that is, a decrease in the accuracy of the RC oscillator. And if the two reference current sources Ic and Ir of the charging current source module are mismatched, the accuracy of the RC oscillator will also be reduced.

[0006] In addition, the above analysis is based on the case of an ideal comparator. The actual comparator output does not flip immediately after V1 or V2 rises to Vf. Instead, there is a delay td, that is, after V1 or V2 rises to Vf, it still needs to rise for a delay td before the comparator output flips. This delay td will also change with changes in temperature and power supply voltage, thereby deteriorating the accuracy of the RC oscillator output clock frequency.

[0007] Therefore, in the prior art, the accuracy of the RC oscillator output clock is improved by the following three means:

[0008] The first is to calibrate the reference resistor Rf. The reference resistor Rf is calibrated by a binary trimming code. Different trimming code values ​​correspond to the size of the resistance value in the access resistor. The unit resistor is formed by compensating each other with the positive temperature coefficient and the negative temperature coefficient to reduce the impact of temperature changes on accuracy. However, the selection of the unit resistance value is limited by the actual length and width of the resistor and cannot be very small. When the on-resistance and resistance value of the switch are of the same order of magnitude, the on-resistance of the switch cannot be ignored, the calibration accuracy is low, and the resistance value of the resistor itself is still affected by the process, which means that the calibration step size is also difficult to determine, and there are a large number of redundant bits after calibration, which increases the chip area and cost.

[0009] The second is to calibrate the switch capacitor. The switch capacitor is calibrated through a binary trim code, and the gate of the MOS tube that controls the capacitor is laser trimmed and the current mirror is weakly pulled down to control the size of the switch capacitor connected to the RC oscillator. However, the use of trimmed capacitors requires consideration of driving issues, and the delay in the driving circuit will affect the clock accuracy. And similar to the reference resistor calibration solution, there are a lot of redundant bits after the capacitor is calibrated, wasting chip area.

[0010] The third is to chop the charging current. By chopping the two charging currents, the current generated by the current source is averaged, but the chopping process only solves the problem of charging current mismatch. It is still necessary to combine the above two methods to calibrate the reference resistor or switch capacitor to improve the clock accuracy.

[0011] Therefore, when calibrating resistance, capacitance or current, the above three existing trimming methods not only have a large trimming code step size, which easily generates a large number of redundant bits during the calibration process, but also the simple binary trimming circuit has a poor monotonicity problem due to the uncertain mismatch between the elements, resulting in large positive and / or negative output glitches during the switch switching process, affecting the accuracy of the clock signal. Summary of the invention

[0012] Based on this, it is necessary to provide a high-precision current-calibrated RC oscillator that can adjust and calibrate the output clock of the RC oscillator, increase the current calibration monotonicity of the RC oscillator, reduce output glitches, and improve the output clock accuracy in order to address the above technical problems.

[0013] In a first aspect, the present application provides a high-precision current-calibrated RC oscillator, comprising a segmented current calibration module, an operational amplifier module, a reference resistor, and a closed-loop feedback module; the input end of the segmented current calibration module is connected to an external input current and a trimming code, the first output end of the segmented current calibration module is connected to one end of the reference resistor and the negative input end of the operational amplifier module, the second output end of the segmented current calibration module is connected to the closed-loop feedback module and the positive input end of the operational amplifier module; the closed-loop output end of the operational amplifier module is connected to the closed-loop feedback module; the other end of the reference resistor is connected to a common ground;

[0014] The segmented current calibration module is used to output a trimmed current and a fixed current according to the input external input current and the trimming code; the fixed current generates a positive input voltage at the positive input end of the operational amplifier module, and the trimmed current and the reference resistor generate a negative input voltage at the negative input end of the operational amplifier module;

[0015] The operational amplifier module is used to amplify, filter and oscillate the positive input voltage and the negative input voltage, and output a clock signal;

[0016] The closed-loop feedback module is used to adaptively adjust the magnitude of the positive input voltage according to the frequency of the clock signal so that the frequency of the clock signal reaches the target frequency.

[0017] In one embodiment, the trimming code includes a decoding bit and a reserved bit, and the segmented current calibration module includes:

[0018] A thermometer decoding unit, used to convert the decoded bits of the trimming code into a thermometer code;

[0019] The segmented digital-to-analog conversion unit is connected to the thermometer decoding unit and includes multiple calibration sub-circuits for controlling the on or off of each calibration sub-circuit according to the external input current, the thermometer code and the reserved bit of the trimming code to generate the corresponding trimming current and the fixed current.

[0020] In one embodiment, the segmented digital-to-analog conversion unit further includes:

[0021] The bias voltage output circuit is used to generate at least two mirror branch currents according to the external input current, and output corresponding bias voltages according to the mirror branch currents.

[0022] In one embodiment, the multi-channel calibration sub-circuit includes at least one fixed output sub-circuit, and the segmented digital-to-analog conversion unit further includes:

[0023] The fixed current output circuit is connected to the bias voltage output circuit and includes at least one fixed output sub-circuit, which is used to control the at least one fixed output sub-circuit to be turned on or off according to the external input current and the bias voltage to output the fixed current.

[0024] In one embodiment, the trimmed current includes a first calibration sub-current and a second calibration sub-current, the multi-channel calibration sub-circuit includes a trimmed output sub-circuit, and the segmented digital-to-analog conversion unit further includes:

[0025] A first trimming circuit, connected to the bias voltage output circuit, comprising at least seven trimming output sub-circuits, for controlling the conduction or cutoff of at least seven trimming output sub-circuits according to the thermometer code and the bias voltage, and outputting the first calibration sub-current;

[0026] The second trimming circuit is connected to the bias voltage output circuit and includes at least five trimming output sub-circuits, which are used to control the conduction or cutoff of at least five trimming output sub-circuits according to the reserved bits of the trimming code and the bias voltage to output the second calibration sub-current.

[0027] In one embodiment, the bias voltage includes a first bias voltage and a second bias voltage, and the trimming output subcircuit includes a calibration current source tube, a first cascode tube, a second cascode tube, and a code-controlled switch;

[0028] The gate of the calibration current source tube is connected to the external input current, the source of the calibration current source tube is connected to the power supply voltage, and the drain of the calibration current source tube is connected to one end of the code-controlled switch;

[0029] The other end of the code-controlled switch is connected to the source of the first cascode transistor;

[0030] The gate of the first cascode transistor is connected to the second bias voltage, and the drain of the first cascode transistor is connected to the source of the second cascode transistor;

[0031] The gate of the second cascode transistor is connected to the first bias voltage, and the drain of the second cascode transistor is connected to the negative input terminal of the operational amplifier module.

[0032] In one embodiment, the fixed output subcircuit includes a fixed current source tube, a third cascode tube, and a fourth cascode tube.

[0033] The gate of the fixed current source tube is connected to the external input current, the source of the fixed current source tube is connected to the power supply voltage, and the drain of the fixed current source tube is connected to the source of the third cascode tube;

[0034] The gate of the third cascode transistor is connected to the second bias voltage, and the drain of the third cascode transistor is connected to the source of the fourth cascode transistor;

[0035] The gate of the fourth cascode transistor is connected to the first bias voltage, and the drain of the fourth cascode transistor is connected to the positive input terminal of the operational amplifier module.

[0036] In one embodiment, the bias voltage output circuit includes PMOS transistors MP1, MP2, MP3 and NMOS transistors MN1, MN2.

[0037] The gate of the PMOS tube MP1 is connected to the gates of the PMOS tubes MP2 and MP3; the drain of the PMOS tube MP1 is connected to the common ground, and the drain of the PMOS tube MP2 is connected to the drain of the NMOS tube MN1; the source of the NMOS tube MN1 is connected to the common ground, and the gate of the NMOS tube MN1 is connected to the gate of the second cascode tube; the drain of the PMOS tube MP3 is connected to the drain of the NMOS tube MN2; the source of the NMOS tube MN2 is connected to the common ground, and the gate of the NMOS tube MN2 is connected to the gate of the first cascode tube;

[0038] The sources of the PMOS tubes MP1, MP2 and MP3 are all connected to the power supply voltage.

[0039] In one embodiment, the operational amplifier module includes a low-pass filter, a voltage-controlled oscillator, and a frequency divider.

[0040] The negative input terminal of the low-pass filter is connected to the first output terminal of the segmented current calibration module, and the positive input terminal of the low-pass filter is connected to the second output terminal of the segmented current calibration module;

[0041] The output end of the low-pass filter is connected to the input end of the voltage-controlled oscillator;

[0042] The output end of the voltage controlled oscillator is connected to the input end of the frequency divider; and the closed-loop output end of the frequency divider is connected to the closed-loop feedback module.

[0043] In one embodiment, the closed-loop feedback module includes closed-loop switches S1, S2 and a closed-loop capacitor C by , C sw ,

[0044] One end of S1 is connected to the second output end of the segmented current calibration module, and the other end of S1 is connected to C sw One end, C sw The other end of C is connected to the public ground; by Connect in parallel with S1 and C sw Both ends of S2 are connected in parallel with C sw both ends of .

[0045] The above-mentioned high-precision current-calibrated RC oscillator performs segmented digital-to-analog conversion on the external input trimming code through the segmented current calibration module, realizes the determination of the minimum trimming step, reduces the calibration redundancy of the external input current, increases the calibration monotonicity of the RC oscillator, thereby reducing the output burrs in the external input current calibration process and improving the output clock signal accuracy. The output of the clock signal is realized through the operational amplifier module, and the size of the positive input voltage of the operational amplifier module is adaptively adjusted according to the frequency of the clock signal through the closed-loop feedback module to achieve impedance matching, complete the locking of the target frequency of the clock signal, and further improve the accuracy of the output clock. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments of the present application or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 is a circuit diagram of a traditional RC oscillator in the background technology;

[0048] Figure 2 A block diagram of a high-precision current-calibrated RC oscillator in one embodiment;

[0049] Figure 3 is a structural block diagram of a segmented current calibration module in one embodiment;

[0050] Figure 4 A block diagram of a 3-bit thermometer decoder in one embodiment;

[0051] Figure 5 is a circuit diagram of a segmented digital-to-analog conversion unit in one embodiment;

[0052] Figure 6 is a transfer characteristic curve between the trimming current IR and the eight-bit binary trimming code S<7:0> in one embodiment;

[0053] Figure 7 A circuit diagram of an RC oscillator for high-precision current calibration in one embodiment;

[0054] Figure 8 FIG. 4 is a histogram of Monte Carlo simulation results of a ratio IC / IR of a fixed current IC to an adjusted current IR in one embodiment. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0056] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the" and the like involved in this application do not indicate a quantity limitation, and may indicate the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "multiple" involved in this application refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there may be three relationships, for example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", "third" and the like involved in the present application are merely used to distinguish similar objects and do not represent a specific ordering of the objects.

[0057] like Figure 2 As shown, a high-precision current-calibrated RC oscillator is provided, including a segmented current calibration module 1, an operational amplifier module 2, a reference resistor 3, and a closed-loop feedback module 4.

[0058] The input end of the segmented current calibration module 1 is connected to the external input current I ref And repair code S<n,0> The first output end of the segmented current calibration module 1 is connected to one end of the reference resistor 3 and the negative input end of the operational amplifier module 2, and the other end of the reference resistor 3 is connected to the common ground. The second output end of the segmented current calibration module 1 is connected to the closed-loop feedback module 4 and the positive input end of the operational amplifier module. The closed-loop output end of the operational amplifier module 2 is connected to the closed-loop feedback module 4. The other end of the closed-loop feedback module is grounded.

[0059] The segmented current calibration module 1 is used to adjust the external input current I according to the input ref And repair code S <n:0>, output trimming current IR and fixed current IC.

[0060] Specifically, the adjustment code S <n:0>, n∈N + , represents an (n+1)-bit binary adjustment code. <n:0>The segmented current calibration module 1 is divided into x decoding bits and [(n+1)-x] reserved bits. ref The segmented current calibration module 1 outputs a fixed current IC according to the external input current I ref , x decoding bits and [(n+1)-x] reserved bits are used to output different magnitudes of trimmed current IR. The fixed current IC generates a positive input voltage VC at the positive input terminal of the operational amplifier module 2, and the trimmed current IR and the reference resistor 3 generate a negative input voltage VR at the negative input terminal of the operational amplifier module 2.

[0061] The operational amplifier module 2 is used to amplify, filter and oscillate the positive input voltage VC and the negative input voltage VR, and output a clock signal CLK.

[0062] The closed-loop feedback module 4 is used to adaptively adjust the magnitude of the positive input voltage VC according to the frequency of the clock signal CLK, so that the frequency of the clock signal CLK reaches a target frequency.

[0063] In this embodiment, the segmented current calibration module 1 performs segmented digital-to-analog conversion on the external input trimming code, thereby realizing the determination of the minimum trimming step (i.e., the reserved bit of the trimming code), reducing the calibration redundancy of the external input current, and increasing the monotonicity of the RC oscillator calibration, thereby reducing the output burrs in the external input current calibration process and improving the accuracy of the output clock signal. The output of the clock signal is realized through the operational amplifier module 2, and the magnitude of the positive input voltage of the operational amplifier module is adaptively adjusted according to the frequency of the clock signal through the closed-loop feedback module 4 to realize impedance matching, complete the locking of the target frequency of the clock signal, and further improve the accuracy of the output clock.

[0064] like Figure 3 As shown, a structural block diagram of a segmented current calibration module 1 is provided.

[0065] In one embodiment, if Figure 3 As shown, the segmented current calibration module 1 includes a thermometer decoding unit 10 and a segmented digital-to-analog conversion unit 11 .

[0066] The input end of the thermometer decoding unit 10 is connected to the decoding bits of the trimming code, and is used to convert the decoding bits of the trimming code into thermometer codes.

[0067] Specifically, the external input adjustment code is an 8-bit binary code, the high-order bits S7, S6, and S5 in the adjustment code are set as decoding bits, and the low-order bits S4, S3, S2, S1, and S0 are set as reserved bits. Figure 3 The thermometer decoding unit 10 shown in the figure is connected to the S7, S6, S5 decoding bits for binary decoding conversion, and then outputs the seven-bit thermometer code Sa~Sg. The last five reserved bits are still input into the segmented digital-to-analog conversion unit 11 in binary form. The thermometer decoding unit 10 can be as follows Figure 4 3-bit thermometer decoder shown.

[0068] Exemplarily, the truth table of a 3-bit thermometer encoder is shown in Table 1 below:

[0069] Table 1

[0070]

[0071] The segmented digital-to-analog conversion unit 11 includes multiple calibration subcircuits. The input end of each calibration subcircuit is connected to the external input current I ref , the corresponding reserved bit of the thermometer code or the trimming code. The segmented digital-to-analog conversion unit 11 is used to convert the external input current I ref , the reserved bits of the thermometer code and the trimming code, control the on or off of each of the calibration sub-circuits, and generate the corresponding trimming current IR and the fixed current IC.

[0072] In this embodiment, the thermometer decoding unit 10 is used to implement the decoding conversion of the decoding bits in the binary trimming code. By setting the three high-order bits of the trimming code as decoding bits, it is ensured that more current coarse adjustment outputs can be performed during current calibration without occupying too much chip area. The low-order bits retain the binary code for current fine adjustment, and the calibration subcircuit controlled by the least significant bit outputs the minimum current, thereby ensuring the accuracy of the trimming current output by the entire segmented current calibration module 1.

[0073] In one embodiment, if Figure 3 As shown, the segmented digital-to-analog conversion unit 11 further includes a bias voltage output circuit 111 for outputting a bias voltage according to an external input current I ref , generating at least two mirror branch currents, and outputting corresponding bias voltages V according to the mirror branch currents P Wherein, the bias voltage V P Acting on each calibration sub-circuit, the electronic devices in the calibration sub-circuit work in the saturation region.

[0074] Preferably, the calibration subcircuit comprises a fixed output subcircuit and a trimmed output subcircuit.

[0075] like Figure 3 As shown, at least one fixed output subcircuit constitutes a fixed current output circuit 112 of the segmented digital-to-analog conversion unit 11. The fixed current output circuit 112 is connected to the bias voltage output circuit 111 and is only affected by the external input current I ref and bias voltage V P The influence of the fixed output sub-circuit is controlled to be turned on or off, and the fixed current IC is output. Therefore, the second output end of the segmented digital-to-analog conversion unit 11 outputs the fixed current IC.

[0076] like Figure 3 As shown, the trimming output subcircuit is divided into a trimming output subcircuit controlled by a thermometer code and a trimming output subcircuit controlled by a reserved bit of a trimming code.

[0077] Specifically, at least seven trimming output sub-circuits controlled by thermometer coding constitute the first trimming circuit 113 of the segmented digital-to-analog conversion unit 11. The first trimming circuit 113 is connected to the bias voltage output circuit, wherein the conduction and cutoff of each trimming output sub-circuit are controlled by the external input current I ref , Thermometer code bit Sa~Sg, bias voltage V P The first calibration sub-current IR1 is output.

[0078] At least five trimming output sub-circuits controlled by the reserved bits of the trimming code constitute the second trimming circuit 114 of the segmented digital-to-analog conversion unit 11. The second trimming circuit 114 is connected to the bias voltage output circuit, wherein the conduction and cutoff of each trimming output sub-circuit are controlled by the external input current I ref , the reserved bit of the trim code, the bias voltage V P The second calibration sub-current IR2 is outputted.

[0079] The trimming current IR output by the segmented digital-to-analog conversion unit 11 includes a first calibration sub-current IR1 and a second calibration sub-current IR2 .

[0080] Optionally, the trimming current IR further includes a fixed trimming sub-current IR3 in addition to the first trimming sub-current IR1 and the second trimming sub-current IR2 . The fixed trimming sub-current IR3 can be obtained by at least one fixed output sub-circuit connected in parallel with the first trimming circuit 113 .

[0081] In this embodiment, the monotonicity of the current calibration is ensured by fixing the current output circuit 112, the first trimming circuit 113 and the second trimming circuit 114, thereby reducing the output glitches generated during the current calibration process, and by performing segmented trimming on the trimming current IR, the calibration of the RC oscillator output clock frequency deviation under different process angles or temperatures or power supply voltages is achieved.

[0082] like Figure 5 As shown, a circuit diagram of a segmented digital-to-analog conversion unit 11 is provided.

[0083] In one embodiment, if Figure 5 As shown, the bias voltage output circuit 111 includes PMOS transistors MP1, MP2, MP3 and NMOS transistors MN1, MN2.

[0084] The gate of the PMOS tube MP1 is connected to the gates of the PMOS tubes MP2 and MP3; the drain of the PMOS tube MP1 is connected to the external input current I ref , the drain of the PMOS tube MP2 is connected to the drain of the NMOS tube MN1; the source of the NMOS tube MN1 is connected to the common ground, and the gate of the NMOS tube MN1 is connected to the gate of the second cascode tube; the drain of the PMOS tube MP3 is connected to the drain of the NMOS tube MN2; the source of the NMOS tube MN2 is connected to the common ground, and the gate of the NMOS tube MN2 is connected to the gate of the first cascode tube; the sources of the PMOS tubes MP1, MP2 and MP3 are all connected to the power supply voltage.

[0085] The PMOS tubes MP1, MP2, and MP3 form a current mirror. MP2 and MP3 respectively convert the external reference current I ref The mirrored currents are mirrored to the respective branches to generate two mirrored branch currents. The mirrored branch currents and the external reference current I ref There is a proportional relationship. Assume that the mirror branch current of MP2 and MP3 is K×I ref , the current flows through MN1 and MN2 respectively. At this time, MN1 and MN2 can be equivalent to resistors with resistance R, generating a first bias voltage V P1 and the second bias voltage V P2 Among them, V P1 、V P2 Size equal to K×I ref ×R.

[0086] In one embodiment, the trimming output subcircuit includes a calibration current source tube, a first cascode tube, a second cascode tube, and a code-controlled switch.

[0087] For example, Figure 5 Taking a certain trimming output sub-circuit shown in FIG as an example, the connection relationship between the calibration current source tube MP4, the first cascode tube MP5, the second cascode tube MP6 and the code-controlled switch Sg is as follows: the gate of the calibration current source tube MP4 is connected to the external input current I ref The source of the calibration current source tube MP4 is connected to the power supply voltage, and the drain of the calibration current source tube MP4 is connected to one end of the code-controlled switch Sg; the other end of the code-controlled switch Sg is connected to the source of the first cascode tube MP5; the gate of the first cascode tube MP5 is connected to the second bias voltage V P2 The drain of the first cascode transistor MP5 is connected to the source of the second cascode transistor MP6; the gate of the second cascode transistor MP6 is connected to the first bias voltage V P1 The drain of the second common-source common-gate transistor MP6 is connected to the negative input terminal of the operational amplifier module.

[0088] in, Figure 4 Among them, MP4, MP16, MP13, MP10, MP22, MP25, and MP28 are all PMOS calibration current source tubes, MP5, MP11, MP14, MP17, MP23, MP26, and MP29 are all PMOS first cascode tubes, and MP6, MP12, MP15, MP18, MP24, MP27, and MP30 are all PMOS second cascode tubes. All calibration current source tubes and PMOS tube MP1 form a current mirror, which is connected to the external reference current I ref The mirror branch current. The first bias voltage V P1 Control each of the second common-source common-gate transistors to work in the saturation region, and the second bias voltage V P2 Each of the first common-source common-gate transistors is controlled to operate in a saturation region.

[0089] Specifically, Figure 5 In the first trimming circuit 113, the code-controlled switches of the seven trimming output sub-circuits are respectively controlled by the seven-bit thermometer code Sa~Sg, and are turned on at a high level. The first calibration sub-current IR1 output by the first trimming circuit 113 is the sum of the output currents of the seven trimming output sub-circuits, wherein the current magnitude of each path when turned on is 500nA, and the current magnitude when turned off is 0.

[0090] Specifically, Figure 5 In the second trimming circuit 114, the code-controlled switches of the five trimming output sub-circuits are respectively controlled by the binary coding of the lower five bits of the trimming code S4, S3, S2, S1, and S0, and are turned on at a high level. The control sub-circuits corresponding to S3 and S2 are not drawn in the figure. The current magnitude of the code-controlled switch S4 that is turned on is 250nA, the current magnitude of the code-controlled switch S3 that is turned on is 125nA, the current magnitude of the code-controlled switch S2 that is turned on is 62.5nA, the current magnitude of the code-controlled switch S1 that is turned on is 31.25nA, and the current magnitude of the code-controlled switch S0 that is turned on is 15.625nA. The second calibration sub-current IR2 output by the second trimming circuit 114 is the sum of the output currents of the five trimming output sub-circuits.

[0091] In this embodiment, different trimming current IR outputs are obtained by configuring different 8-bit binary input signals S<7:0> to obtain calibration capability. For example, when S<7:0>= 1000 0000, the upper 3 bits are 100, and the thermometer code 0001111 is obtained after passing through the 3-bit thermometer decoding unit, which means that the currents controlled by the 4 thermometer codes are added; the lower 5 bits are 00000, which means that the binary code part does not contribute to the current at this time, and there is also a fixed calibration sub-current IR3=1μA, and the total trimming current IR = 500nA×4 + 1μA = 3μA.

[0092] Figure 6 The transfer characteristic curve between the trimming current IR output by the segmented current calibration module 1 and the input trimming code S<7:0> is given, where the horizontal axis is the decimal representation of the input trimming code binary code value, and the decimal value corresponding to the 8-bit binary code is 0~255, with a total of 2^8 = 256 code values, and the vertical axis is the magnitude of the trimming current IR. Setting the default initial input trimming code value to the middle bit of the entire input trimming code range can more clearly show the monotonicity of the segmented current calibration module 1 upward or downward trimming. Therefore, when the trimming code value of M1 is set to 128 (1000 0000), the corresponding trimming current IR is 3uA. When trimming downward, the corresponding M3 sets the trimming code value to the lowest 0, and the trimming current IR is only 1uA; when trimming upward, the corresponding M4 sets the trimming code value to the highest 255, and the maximum trimming current IR is 4.984uA. If the calibration monotonicity is poor, the curve will have multiple high and low changes, so Figure 5 It can be seen that the monotonicity of the segmented current calibration module 1 is high. M2 reflects the minimum amount of trimming current IR that can be trimmed by the segmented current calibration module 1, that is, the trimming step. It can be seen that compared with M1, the code value of M2 is only increased by 1, and the corresponding trimming current IR increases by 0.016uA. That is to say, for every increase of 1 bit in the trimming code value of the segmented current calibration module 1, the output of the trimming current IR increases by 0.016uA, and the trimming step is 0.016 / 3=0.53%, with high trimming accuracy.

[0093] In one embodiment, the fixed output subcircuit includes a fixed current source tube, a third cascode tube, and a fourth cascode tube.

[0094] For example, Figure 5 Taking the fixed output subcircuit shown in as an example, the connection relationship between the fixed current source tube MP7, the third cascode tube MP8, and the fourth cascode tube MP9 is as follows: the gate of the fixed current source tube MP7 is connected to the external input current I ref The source of the fixed current source tube MP7 is connected to the power supply voltage, the drain of the fixed current source tube MP7 is connected to the source of the third cascode tube MP8; the gate of the third cascode tube MP8 is connected to the second bias voltage V P2 The drain of the third cascode transistor MP8 is connected to the source of the fourth cascode transistor MP9; the gate of the fourth cascode transistor MP9 is connected to the first bias voltage V P1 The drain of the fourth common-source common-gate transistor MP9 is connected to the positive input terminal of the operational amplifier module.

[0095] In detail, Figure 4 In the circuit, the fixed current source tube MP7 and the PMOS tube MP1 form a current mirror, which is connected to the external reference current I ref The mirror branch current. The first bias voltage V P1 The fourth common-source common-gate transistor MP9 is controlled to operate in the saturation region, and the second bias voltage V P2 The third cascode transistor MP8 is controlled to operate in a saturation region.

[0096] like Figure 7 As shown, a circuit structure diagram of a high-precision current-calibrated RC oscillator is provided.

[0097] In one embodiment, if Figure 7 As shown, the operational amplifier module 2 includes a low-pass filter 201 , a voltage-controlled oscillator 202 , and a frequency divider 203 .

[0098] The negative input end of the low-pass filter 201 is connected to the first output end of the segmented current calibration module 1, and the positive input end of the low-pass filter 201 is connected to the second output end of the segmented current calibration module 1; the output end of the low-pass filter 201 is connected to the input end of the voltage-controlled oscillator 202; the output end of the voltage-controlled oscillator 202 is connected to the input end of the frequency divider 203; the closed-loop output end of the frequency divider 203 is connected to the closed-loop feedback module 4; the filter capacitor C p One end is connected to the output end of the low-pass filter 201, and the other end is connected to the common ground.

[0099] The low-pass filter 201 includes an operational amplifier Amp and a filter capacitor C p The negative input terminal of the operational amplifier Amp is connected to the first output terminal of the segmented current calibration module 1, the positive input terminal is connected to the second output terminal of the segmented current calibration module 1, and the output terminal is connected to the input terminal of the voltage-controlled oscillator 202. The filter capacitor C p One end is connected to the output end of the operational amplifier Amp, and the other end is connected to the common ground.

[0100] Specifically, the fixed current IC generates a positive input voltage VC at the positive input terminal of the operational amplifier Amp, and the trimming current IR and the reference resistor R ref A negative input voltage VR is generated at the negative input terminal of the operational amplifier Amp. The two are amplified by the operational amplifier Amp and then by the filter capacitor C p Perform low-pass filtering to generate an output voltage V ctrl . Output voltage V ctrl After the signal is oscillated by the voltage-controlled oscillator 202, an oscillation signal of a certain frequency is output. After the oscillation signal passes through the frequency divider 203, three divided clock signals are output, including the clock signal CLK and two non-overlapping closed-loop clock signals φ1 and φ2. Among them, the frequencies of φ1, φ2 and CLK are different frequency division results of the frequency f of the oscillation signal after passing through the frequency divider 203. The frequencies of the closed-loop clock signals φ1 and φ2 are f sw The size of is f / N1 and the signal is inverted, the size of the frequency f_CLK of CLK is f / N2, and N1 and N2 represent different frequency division coefficients.

[0101] More specifically, the closed-loop feedback module 4 uses the frequency f of the closed-loop clock signals φ1 and φ2 sw , adaptively adjust the VC voltage at the positive input terminal of the operational amplifier Amp so that the frequency f_CLK of the output clock signal CLK reaches the target frequency.

[0102] In this embodiment, an oscillation signal is generated by a low-pass filter 201 and a voltage-controlled oscillator 202, and the oscillation signal is divided by a frequency divider 203 to generate an output clock signal and a closed-loop clock signal. The closed-loop clock signal is used to adjust the closed-loop feedback module to achieve impedance matching at the input end of the operational amplifier, complete the locking of the target frequency of the output clock signal, and further improve the accuracy of the output clock signal.

[0103] In one embodiment, if Figure 7 As shown, the closed-loop feedback module 4 includes switches S1, S2 and a capacitor C by , C sw One end of S1 is connected to the second output end of the segmented current calibration module 1, and the other end of S1 is connected to C sw One end, C sw The other end of C is connected to the public ground; by Connect in parallel with S1 and C sw Both ends of S2 are connected in parallel with C sw both ends of .

[0104] Specifically, when the second output terminal of the segmented current calibration module 1 outputs the fixed current IC, the closed-loop feedback module 4 is charged, and a positive input voltage VC is generated at the positive input terminal of the operational amplifier module 2. The closed-loop clock signals φ1 and φ2 output from the two closed-loop output terminals of the frequency divider 203 act on the switches S1 and S2 in the closed-loop feedback module 4. If the frequencies f of the closed-loop clock signals φ1 and φ2 are sw If the value is small, the opening and closing speed of S1 and S2 is slow, which means that the frequency f_CLK of the output clock signal CLK is lower than the target frequency. At this time, the closed-loop capacitor C sw The equivalent resistance R sc =1 / f sw ·C sw will increase, and the positive input voltage VC of the positive input terminal of the operational amplifier module 2 will also increase accordingly, and the output voltage V ctrl The gain of the voltage-controlled oscillator 202 is positive, which eventually increases the frequency of the clock signal CLK. The opposite is also true. The frequency of the clock signal f_CLK = (IC / IR)·(N / R ref ·C sw ), N=N1 / N2. Capacitor C by The function is to reduce the fluctuation of the positive input voltage VC. Through such a closed-loop negative feedback, the frequency of the clock signal CLK is always stable within the target frequency range, achieving high-precision clock signal output.

[0105] In an exemplary embodiment, a high-precision current-calibrated RC oscillator is provided, comprising: Figure 7 The circuit structure shown in FIG. 1 includes a segmented current calibration module 1 as follows: Figure 3 The circuit structure shown in FIG. Each module / unit can realize the functions described in the above embodiments.

[0106] Figure 8 The Monte Carlo simulation result of the ratio IC / IR of the fixed current IC and the trimmed current IR output by the segmented current calibration module 1 is shown in Figure 1. The results of 1000 Monte Carlo simulations show that the 3sigma size of the IC / IR ratio mismatch is only 0.345% of the average value (the average value is 2, and the 1sigma is 0.0023).

[0107] The RC oscillator described in this exemplary embodiment is applied under the typical conditions of TT process angle, 27°C, and 5V power supply voltage. The frequency of the RC oscillator output clock signal is 60MHz. At this time, the input trimming code of the segmented current calibration module 1 is 10000000, and the output trimming current IR is 3μA. When the conditions change to SS process angle, 27°C, and 5V power supply voltage, the frequency of the RC oscillator output clock signal is reduced to 43.02MHz due to process changes. At this time, the input trimming code value of the segmented calibration current DAC can be changed to 0100 1000, that is, the trimming current IR is trimmed to 2.125μA, and the frequency is pulled back to 60.27MHz, which is only 0.45% different from the nominal frequency of 60MHz.

[0108] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0109] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0110] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present application. It should be noted that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A high-precision current-calibrated RC oscillator, characterized in that: It includes a segmented current calibration module, an operational amplifier module, a reference resistor, and a closed-loop feedback module; the input end of the segmented current calibration module is connected to an external input current and a trimming code, the first output end of the segmented current calibration module is connected to one end of the reference resistor and the negative input end of the operational amplifier module, the second output end of the segmented current calibration module is connected to the closed-loop feedback module and the positive input end of the operational amplifier module; the closed-loop output end of the operational amplifier module is connected to the closed-loop feedback module; the other end of the reference resistor is connected to a common ground; The segmented current calibration module is used to output a trimmed current and a fixed current according to the input external input current and the trimming code; the trimming code includes a decoding bit and a reserved bit, and the segmented current calibration module includes a thermometer decoding unit and a segmented digital-to-analog conversion unit, and the thermometer decoding unit is used to convert the decoding bit of the trimming code into a thermometer code; The segmented digital-to-analog conversion unit is connected to the thermometer decoding unit and includes a multi-channel calibration sub-circuit, which is used to control the conduction or cutoff of each calibration sub-circuit according to the external input current, the thermometer code and the reserved bit of the trimming code to generate the corresponding trimming current and the fixed current; the fixed current generates a positive input voltage at the positive input end of the operational amplifier module, and the trimming current and the reference resistor generate a negative input voltage at the negative input end of the operational amplifier module; Wherein, the segmented digital-to-analog conversion unit further includes a bias voltage output circuit, which is used to generate at least two mirror branch currents according to the external input current, and output a corresponding bias voltage according to the mirror branch current; the multi-channel calibration subcircuit includes at least one fixed output subcircuit, and the segmented digital-to-analog conversion unit further includes a fixed current output circuit, which is connected to the bias voltage output circuit, including at least one fixed output subcircuit, which is used to control at least one fixed output subcircuit to be turned on or off according to the external input current and the bias voltage, and output the fixed current; Wherein, the trimming current includes a first calibration sub-current and a second calibration sub-current, the multi-channel calibration sub-circuit includes a trimming output sub-circuit, and the segmented digital-to-analog conversion unit also includes a first trimming circuit and a second trimming circuit; the first trimming circuit is connected to the bias voltage output circuit, including at least seven trimming output sub-circuits, used to control the conduction or cutoff of at least seven trimming output sub-circuits according to the thermometer code and the bias voltage, and output the first calibration sub-current; the second trimming circuit is connected to the bias voltage output circuit, including at least five trimming output sub-circuits, used to control the conduction or cutoff of at least five trimming output sub-circuits according to the reserved bits of the trimming code and the bias voltage, and output the second calibration sub-current; The operational amplifier module is used to amplify, filter and oscillate the positive input voltage and the negative input voltage, and output a clock signal; The closed-loop feedback module is used to adaptively adjust the magnitude of the positive input voltage according to the frequency of the clock signal so that the frequency of the clock signal reaches the target frequency.

2. The high-precision current-calibrated RC oscillator according to claim 1, characterized in that: The bias voltage includes a first bias voltage and a second bias voltage, and the trimming output subcircuit includes a calibration current source tube, a first cascode tube, a second cascode tube and a code-controlled switch; The gate of the calibration current source tube is connected to the external input current, the source of the calibration current source tube is connected to the power supply voltage, and the drain of the calibration current source tube is connected to one end of the code-controlled switch; The other end of the code-controlled switch is connected to the source of the first cascode transistor; The gate of the first cascode transistor is connected to the second bias voltage, and the drain of the first cascode transistor is connected to the source of the second cascode transistor; The gate of the second cascode transistor is connected to the first bias voltage, and the drain of the second cascode transistor is connected to the negative input terminal of the operational amplifier module.

3. The high-precision current-calibrated RC oscillator according to claim 2, characterized in that: The fixed output subcircuit includes a fixed current source tube, a third cascode tube, and a fourth cascode tube. The gate of the fixed current source tube is connected to the external input current, the source of the fixed current source tube is connected to the power supply voltage, and the drain of the fixed current source tube is connected to the source of the third cascode tube; The gate of the third cascode transistor is connected to the second bias voltage, and the drain of the third cascode transistor is connected to the source of the fourth cascode transistor; The gate of the fourth cascode transistor is connected to the first bias voltage, and the drain of the fourth cascode transistor is connected to the positive input terminal of the operational amplifier module.

4. The high-precision current-calibrated RC oscillator according to claim 1, characterized in that: The bias voltage output circuit includes PMOS tubes MP1, MP2, MP3 and NMOS tubes MN1, MN2. The gate of the PMOS tube MP1 is connected to the gates of the PMOS tubes MP2 and MP3; the drain of the PMOS tube MP1 is connected to the external input current I ref , the drain of the PMOS tube MP2 is connected to the drain of the NMOS tube MN1; the source of the NMOS tube MN1 is connected to the common ground, and the gate of the NMOS tube MN1 is connected to the gate of the second cascode tube; the drain of the PMOS tube MP3 is connected to the drain of the NMOS tube MN2; the source of the NMOS tube MN2 is connected to the common ground, and the gate of the NMOS tube MN2 is connected to the gate of the first cascode tube; The sources of the PMOS tubes MP1, MP2 and MP3 are all connected to the power supply voltage.

5. The high-precision current-calibrated RC oscillator according to claim 1, characterized in that: The operational amplifier module includes a low-pass filter, a voltage-controlled oscillator, and a frequency divider. The negative input terminal of the low-pass filter is connected to the first output terminal of the segmented current calibration module, and the positive input terminal of the low-pass filter is connected to the second output terminal of the segmented current calibration module; The output end of the low-pass filter is connected to the input end of the voltage-controlled oscillator; The output end of the voltage controlled oscillator is connected to the input end of the frequency divider; and the closed-loop output end of the frequency divider is connected to the closed-loop feedback module.

6. The high-precision current-calibrated RC oscillator according to claim 1, characterized in that: The closed-loop feedback module includes switches S1, S2 and a capacitor C by , C sw , One end of S1 is connected to the second output end of the segmented current calibration module, and the other end of S1 is connected to C sw One end, C sw The other end of C is connected to the public ground; by Connect in parallel with S1 and C sw Both ends of S2 are connected in parallel with C sw both ends of .

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