A current source circuit with low temperature coefficient

Abstract

The present application provides a low temperature coefficient current source circuit, which is used in power management system to provide stable reference current value, comprising reference voltage circuit, same temperature coefficient current generating circuit and current difference circuit. Transistor base radio voltage and band gap voltage are provided to the gate of MN1 and MN2 respectively to generate current with same temperature coefficient, and further generate low temperature coefficient current through current difference circuit. The present application obtains low temperature coefficient current source by means of subtracting same temperature coefficient current, and obtains current with lower temperature coefficient than traditional current source. Moreover, only same temperature coefficient current needs to be designed, which simplifies circuit structure and saves area.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit design, and more specifically to a current source circuit with a low temperature coefficient. Background Technology

[0002] In integrated circuits, current sources are circuits that provide the correct bias for operational amplifiers, comparators, oscillators, and even more complex functional systems. Therefore, the performance of the current source circuit determines the performance of other modules. A good current source should have characteristics that are independent of ambient temperature and power supply voltage.

[0003] An ideal current source circuit should provide a current independent of the supply voltage and ambient temperature. Traditional current sources are generated in low-voltage bandgap circuits. Low-voltage bandgap circuits can generate a low-temperature-coefficient voltage across a resistor, thus the current flowing through that resistor also has a low-temperature-coefficient. Other methods for designing low-temperature-coefficient current sources include: applying a positive temperature-coefficient voltage to a resistor with a positive temperature coefficient through the virtual shorting effect of an operational amplifier; and adding a current with a positive temperature coefficient and a current with a negative temperature coefficient to obtain a current with a low temperature coefficient. However, these methods all have their own problems. For resistors with a temperature coefficient, the temperature coefficient is difficult to adjust, and there are matching issues requiring external trimming, while stability must also be considered. For the method of adding currents with positive and negative temperature coefficients, the circuits generating both positive and negative temperature coefficients are complex, occupying a large area and incurring high costs. This invention addresses these problems by proposing a low-temperature-coefficient current source. The low-temperature-coefficient current source described in this invention avoids the design of circuits with positive and negative temperature coefficients, saving power consumption and cost. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides a low temperature coefficient current source circuit. This invention subtracts currents with the same temperature coefficient to obtain a low temperature coefficient current source.

[0005] The technical solution of the present invention is as follows:

[0006] This invention provides a low temperature coefficient current source circuit, comprising a reference voltage circuit, a current generation circuit with the same temperature coefficient, and a current difference circuit.

[0007] The reference voltage circuit includes an operational amplifier, P-type field-effect transistors MP1 and MP2, resistors R1, R2, and R3, and PNP transistors Q1 and Q2. P-type field-effect transistors MP1 and MP2 are of the same size. The emitter width ratio of PNP transistors Q1 and Q2 is Q1:Q2 = 1:N, where N > 1. The emitter of PNP transistor Q1 is connected to the drain of P-type field-effect transistor MP1 through resistor R1. The emitter of transistor Q2 is connected to the drain of MP2 through a series circuit of resistors R2 and R3; the gates of P-type field-effect transistors MP1 and MP2 are connected and connected to the output of the operational amplifier; the positive input of the operational amplifier is connected to the midpoint of the series circuit of resistors R1 and R3, and the negative input of the operational amplifier is connected to the emitter of PNP transistor Q1; the sources of P-type field-effect transistors MP1 and MP2 are connected to the power supply voltage, and the collectors and bases of PNP transistors Q1 and Q2 are grounded;

[0008] The temperature coefficient current generating circuit includes a P-type field-effect transistor (FET) MP3, an N-type field-effect transistor (FET) MN1, and an N-type field-effect transistor (FET) MN2. The gate and drain of the P-type FET MP3 are connected. The gate of the N-type FET MN1 is connected to the emitter of the PNP transistor Q2, and the drain of the N-type FET MN1 is connected to the drain of the P-type FET MP3. The gate of the N-type FET MN2 is connected to the drain of the P-type FET MP2. The source of the P-type FET MP3 is connected to the power supply voltage, and the sources of the N-type FETs MN1 and MN2 are grounded.

[0009] The current differential circuit includes P-type field-effect transistors MP4, MP5, and MP6; the gate of P-type field-effect transistor MP4 is connected to the gate of MP3, and the drain of P-type field-effect transistor MP4 is connected to the drain of MN2; the drain of P-type field-effect transistor MP5 is connected to the drain of N-type field-effect transistor MN2, the gate and drain of P-type field-effect transistor MP5 are shorted, and the gate of P-type field-effect transistor MP5 is connected to the gate of P-type field-effect transistor MP6; the sources of P-type field-effect transistors MP4, MP5, and MP6 are connected to the power supply voltage; the drain of P-type field-effect transistor MP6 is the current output terminal.

[0010] The working mechanism and design method of this invention are as follows:

[0011] The current expression for a field-effect transistor operating in the saturation region has two variables with temperature coefficients: one is the threshold voltage V. th The other is carrier mobility μ. Figure 1 It is the threshold voltage V of a 180nm N-type field-effect transistor. thThe curve showing the change in voltage over temperature, and the threshold voltage V of the field-effect transistor. th The threshold voltage (VT) decreases with increasing temperature, which is called negative temperature dependence, and its rate of change is close to -1 mV / ℃. This value is independent of the transistor size; therefore, for the same type of field-effect transistor, the threshold voltage is consistent. The change in carrier mobility μ with temperature is related to lattice vibrational scattering. Lattice vibrational scattering causes carrier mobility to decrease with increasing temperature. Figure 2 It is a 180nm N-type field-effect transistor V gs -V th The curve of drain current versus temperature under constant conditions, V gs The trend of the gate-source voltage and the current change is the trend of the carrier mobility μ.

[0012] Furthermore, based on the connection relationship, write the current expression:

[0013] I1 = g mn1 (V be -V th )

[0014] I2=g mn2 (V ref -V th )

[0015] Based on the function of the differential circuit, the expression for the differential current can be written as follows:

[0016]

[0017] Where B is the ratio of the width to the length of MP4 and MP3 (i.e., the current mirror ratio), and V... ref It is the bandgap voltage, g mn1 and g mn2 The transconductance of MN1 and MN2, respectively, and V be This is the base-emitter junction voltage of Q2. The equation consists of two factors (transconductance and a polynomial), g mn2 It has a negative temperature coefficient; according to the requirement of a low temperature coefficient, the polynomial within the first set of parentheses must have a positive temperature coefficient. V ref It is a temperature-independent bandgap voltage. V be The first term is negatively correlated with temperature, so the second term is positively correlated with temperature, and the temperature coefficient is modulated by the transconductance ratio and the mirror current ratio B. The third term is due to V. th The multiplier before is negative, so it is also positively correlated with temperature. Multiplying the two factors, within a certain temperature range, yields a current with a temperature coefficient approximately zero. This invention, by carefully setting the ratio B of the current mirror and the dimensions of the two N-type field-effect transistors, can obtain a differential current with a low temperature coefficient within the range of -40℃ to 100℃.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0019] 1. A current source with a low temperature coefficient is obtained by subtracting currents with the same temperature coefficient, resulting in a current with a lower temperature coefficient than that of a traditional current source.

[0020] 2. Avoid using currents with positive and negative temperature coefficients simultaneously; only currents with the same temperature coefficient need to be designed, simplifying the circuit structure and saving area. Attached Figure Description

[0021] Figure 1 The curve of the threshold voltage Vth of a 180 nm N-type field-effect transistor as a function of temperature is shown in the figure, which is a preferred embodiment of the present invention.

[0022] Figure 2 The 180nm N-type field-effect transistor V, which is a preferred embodiment of the present invention gs -V th A graph showing the change of drain current with temperature under constant conditions.

[0023] Figure 3 This is a schematic diagram of the low temperature coefficient current source circuit involved in this invention.

[0024] Figure 4 This is a comparison graph showing the change in current of a low temperature coefficient current source with temperature as a preferred embodiment of the present invention, and the current of a conventional current source. Detailed Implementation

[0025] To make the design steps and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with the embodiments and accompanying drawings. However, it should be particularly emphasized that the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Figure 3 The schematic diagram of the low temperature coefficient current source circuit involved includes a reference voltage circuit, a current generation circuit with the same temperature coefficient, and a current difference circuit.

[0027] The reference voltage circuit includes an operational amplifier, P-type field-effect transistors MP1 and MP2, resistors R1, R2, and R3, and PNP transistors Q1 and Q2. P-type field-effect transistors MP1 and MP2 are of the same size. The emitter width ratio of PNP transistors Q1 and Q2 is Q1:Q2 = 1:N, where N > 1. The emitter of PNP transistor Q1 is connected to the drain of P-type field-effect transistor MP1 through resistor R1. The emitter of transistor Q2 is connected to the drain of MP2 through a series circuit of resistors R2 and R3; the gates of P-type field-effect transistors MP1 and MP2 are connected and connected to the output of the operational amplifier; the positive input of the operational amplifier is connected to the midpoint of the series circuit of resistors R1 and R3, and the negative input of the operational amplifier is connected to the emitter of PNP transistor Q1; the sources of P-type field-effect transistors MP1 and MP2 are connected to the power supply voltage, and the collectors and bases of PNP transistors Q1 and Q2 are grounded;

[0028] The temperature coefficient current generating circuit includes a P-type field-effect transistor (FET) MP3, an N-type field-effect transistor (FET) MN1, and an N-type field-effect transistor (FET) MN2. The gate and drain of the P-type FET MP3 are connected. The gate of the N-type FET MN1 is connected to the emitter of the PNP transistor Q2, and the drain of the N-type FET MN1 is connected to the drain of the P-type FET MP3. The gate of the N-type FET MN2 is connected to the drain of the P-type FET MP2. The source of the P-type FET MP3 is connected to the power supply voltage, and the sources of the N-type FETs MN1 and MN2 are grounded.

[0029] The current differential circuit includes P-type field-effect transistors MP4, MP5, and MP6; the gate of P-type field-effect transistor MP4 is connected to the gate of MP3, and the drain of P-type field-effect transistor MP4 is connected to the drain of MN2; the drain of P-type field-effect transistor MP5 is connected to the drain of N-type field-effect transistor MN2, the gate and drain of P-type field-effect transistor MP5 are shorted, and the gate of P-type field-effect transistor MP5 is connected to the gate of P-type field-effect transistor MP6; the sources of P-type field-effect transistors MP4, MP5, and MP6 are connected to the power supply voltage; the drain of P-type field-effect transistor MP6 is the current output terminal.

[0030] Example:

[0031] This embodiment uses a 5mA low temperature coefficient current source, and the common-mode input voltage of the operational amplifier is 800mV to 1000mV for normal operation.

[0032] Furthermore, in this embodiment, the emitter width ratio of Q1 and Q2 in the bandgap circuit is 1:15, and the values ​​of resistors R1 and R2 are equal, which are 2.6 times that of R3.

[0033] Furthermore, select the width-to-length ratio (W / L). MN2 With a width-to-length ratio of approximately 300, I2 ≈ 5.5 mA. Because the size ratios of MN1 and MN2 need to be matched with the current mirror ratio B, the gate length is increased by a factor of 5 to determine the size of MN1.

[0034] Furthermore, by carefully adjusting the value of B, the temperature coefficient change of the differential current can be observed through simulation, and the optimal current mirror ratio B under the current MN1 and MN2 size configuration can be found.

[0035] After several iterations of the above steps, the aspect ratio of MN1 was finally determined to be 310, the aspect ratio of MN2 to be 62, and the ratio of the current mirror B to be 3.44. Figure 4 This is a comparison of the current variation of the low temperature coefficient current source designed in this invention with that of a traditional current source. The current source of this embodiment can operate normally within a power supply voltage range of 2.5 to 3V, with a current variation of ±0.7%, while the output current variation of the traditional circuit is ±0.95%.

[0036] In summary, the current source designed in this embodiment has a current error of ±0.7% within the temperature range of -40℃ to 100℃, which is better than traditional current source circuits. Moreover, it uses fewer transistors, which can save chip area.

[0037] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A current source circuit with a low temperature coefficient, characterized in that, The circuit includes a reference voltage circuit, a current generation circuit with the same temperature coefficient, and a current difference circuit. The reference voltage circuit includes an operational amplifier, P-type field-effect transistors MP1 and MP2, resistors R1, R2, and R3, and PNP transistors Q1 and Q2. P-type field-effect transistors MP1 and MP2 are of the same size. The emitter width ratio of PNP transistors Q1 and Q2 is Q1:Q2 = 1:N, where N > 1. The emitter of PNP transistor Q1 is connected to the drain of P-type field-effect transistor MP1 through resistor R1. The emitter of transistor Q2 is connected to the drain of MP2 through a series circuit of resistors R2 and R3; the gates of P-type field-effect transistors MP1 and MP2 are connected and connected to the output of the operational amplifier; the positive input of the operational amplifier is connected to the midpoint of the series circuit of resistors R1 and R3, and the negative input of the operational amplifier is connected to the emitter of PNP transistor Q1; the sources of P-type field-effect transistors MP1 and MP2 are connected to the power supply voltage, and the collectors and bases of PNP transistors Q1 and Q2 are grounded; The temperature coefficient current generating circuit includes a P-type field-effect transistor (FET) MP3, an N-type field-effect transistor (FET) MN1, and an N-type field-effect transistor (FET) MN2. The gate and drain of the P-type FET MP3 are connected. The gate of the N-type FET MN1 is connected to the emitter of the PNP transistor Q2, and the drain of the N-type FET MN1 is connected to the drain of the P-type FET MP3. The gate of the N-type FET MN2 is connected to the drain of the P-type FET MP2. The source of the P-type FET MP3 is connected to the power supply voltage, and the sources of the N-type FETs MN1 and MN2 are grounded. The current differential circuit includes P-type field-effect transistors MP4, MP5, and MP6; the gate of P-type field-effect transistor MP4 is connected to the gate of MP3, and the drain of P-type field-effect transistor MP4 is connected to the drain of MN2; the drain of P-type field-effect transistor MP5 is connected to the drain of N-type field-effect transistor MN2, the gate and drain of P-type field-effect transistor MP5 are shorted, and the gate of P-type field-effect transistor MP5 is connected to the gate of P-type field-effect transistor MP6; the sources of P-type field-effect transistors MP4, MP5, and MP6 are connected to the power supply voltage; the drain of P-type field-effect transistor MP6 is the current output terminal.

2. The low temperature coefficient current source circuit according to claim 1, characterized in that, The emitter width ratio of the PNP transistor Q1 and the PNP transistor Q2 is 1:

15.

3. The low temperature coefficient current source circuit according to claim 2, characterized in that, The values ​​of resistors R1 and R2 are equal, and are 2.6 times that of resistor R3.

4. A low temperature coefficient current source circuit according to claim 3, characterized in that, The aspect ratio of the N-type field-effect transistor MN1 is 310, the aspect ratio of the N-type field-effect transistor MN2 is 62, and the ratio of the current mirror is B = 3.44, where B is the ratio of the aspect ratios of MP4 and MP3.

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