JPH0290306A - Current reference circuit unrelated to temperature - Google Patents

Abstract

PURPOSE: To obtain a current reference which is irrelevant to temperature by putting a p-n junction and a poly-Si resistance in the same parallel circuit and applying the same voltage to both the ends, and then balancing voltage variations at both the ends caused by temperature variations. CONSTITUTION: Two parallel circuits are constituted between voltage sources Vdd and Vss . One circuit includes a 1st complementary circuit which is in series with the diode 11 and the other includes a 2nd complementary circuit which is in series with the poly-Si resistance 13. The (n) channel devices of the respective circuits are connected to Vdd , a common gate is connected to the connection point between the poly-Si resistance 13 and the series (n) channel device 9, and the common gate of the (p) channel devices 7 and 9 of the respective circuits is connected to the connection point between the diode 11 and series device 7. Therefore, voltage variations at both the ends of the diode 11 and poly-Si resistance 13 with temperature substantially cancel each other. The extent of the cancellation relates to the doping level of the poly-Si. The resistance value is so selected as to obtain adequate performance as to not only temperature compensation, but also all operations.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a temperature independent OMO8 current reference source.

BACKGROUND OF THE INVENTION Temperature-independent current sources have many applications in various fields. For example, circuits that perform precise analog functions, such as operational amplifiers, require a current source. When designing an operational amplifier, the current bias for it is determined to achieve the desired performance. If the current thereto changes with temperature changes, the operational amplifier will experience undesirable changes in its characteristics due to this current change. Therefore, it is necessary to keep the current in such circuits, as well as other known circuits, substantially independent of temperature.

In the past, there have been numerous attempts to provide temperature independent current sources. - Previous attempts to control current sources have been complex and economically costly indirect methods. Conventional approaches utilize a reference device that produces a result that is proportional to the difference between a device with a positive temperature coefficient of resistance and a reference device with a negative temperature coefficient of resistance. This is in the hope that the resulting difference will result in a more or less stable current with respect to temperature changes. An example is described in the book Analysis and Design of Analog Integrated Circuits by IC Ball R., Gray and Lovato G. Meyer, published by John Wiley & Sons, 2nd edition.

SUMMARY OF THE INVENTION The present invention minimizes the problems of the prior art described above and provides an OMO3 current reference source that is relatively simple and inexpensive to manufacture.

Briefly, this is accomplished by balancing the negative voltage change with temperature change across a solid state device, ie, a pn junction, with the voltage change across a resistor for a given constant current. To this end, the resistance value of the resistor is adjusted negatively with respect to temperature changes, preferably by doping the polysilicon resistor to a predetermined level and adjusting its negative temperature coefficient of resistance. The doping density of a polysilicon resistor determines the temperature coefficient of its resistance, whereas the initial resistance is determined independently by the shape of the resistor.

It has been found that the temperature coefficient of resistance of polysilicon is negative and is a function of its doping density. This is what IE Transactions on Electron Devices, Vol. FD-30.

No. 2 (February 1983), pages 137 to 149. At a polysilicon doping level that results in a resistivity of about 500 ohms/square, its negative temperature coefficient of resistance is roughly commensurate with the p-n junction, up to the first order. In the first approximation, the resistance value of the polysilicon resistor is expressed by the formula R
(T) −R8(1+aΔF). where a is 2100 ppm/℃, ΔT=T−To, and To is the ambient temperature in degrees (room temperature is 300 degrees
K), Ro is the initial resistance value at ambient humidity. Therefore, if you put a pn junction and a polysilicon resistor in the same parallel circuit and apply the same voltage across them, the voltage change at both ends due to temperature change will be balanced out and the temperature-independent current will A reference is obtained.The current through the resistor is then
It is based on the ratio between the voltage across the pn junction and the resistance value of the polysilicon resistor.

In the simplest form of this invention, the current M standard is Vdd and ■s
It includes two parallel circuits between s. One circuit includes a first complementary circuit in series with a diode and the other circuit includes a second complementary circuit in series with a polysilicon resistor. The n-channel devices of each circuit are coupled to Vdd and their common gates are coupled to the node of a complementary device in series with a polysilicon resistor. The common gate of the p-channel device of each circuit is coupled to the node of the complementary device in series with the diode. It is therefore clear that the voltage change across the diode with temperature and the voltage change across the resistor with humidity substantially cancel, and the degree of cancellation is related to the doping level of the resistor. In general, the resistor may have other functions in the circuit besides temperature compensation, so the value chosen for it may be a trade-off.

Resistance values are selected not only for temperature compensation but also for optimum performance in all areas of operation.

Figure 1 shows the simplest form of the current reference circuit of the invention, which produces a current of 17 in the ratio of the voltage across the diode divided by the resistance. . Although other circuits may fulfill this requirement and form part of this invention, the circuit shown is such that this current drop type is maintained regardless of the supply voltage above the minimum determined by the design of the circuit. , which is advantageous in that the desired current is generated and is independent of the power supply. Furthermore, while 0M08 circuits typically have processing dependencies on the MO8 device, this circuit is made with 0MO3 technology and is independent of the Vt of n-channel or p-channel devices. . circuit 1 is 1
It has a pair of p-channel MOS transistors 3, 5, the sources of which are connected to Vdd, and the drains of which are connected to the drains of n-channel MOS transistors 9, respectively. The gates of transistors 3 and 5 are coupled together and to the junction of the drain of transistor 5 and the drain of transistor 9. The gates of transistors 7.9 are coupled together and to the connection point of the drain of transistor 3 and the drain of transistor 7.

The source of transistor 7 is connected to Vs through diode 11.
is coupled to s. On the other hand, the source of transistor 9 is coupled to Vss via polysilicon resistor 13.

This resistor is doped to have the desired negative temperature coefficient of resistance as previously discussed.

The current in each p-channel transistor is the same because they are the same size and should return the same current because they have a common gate-to-lass voltage. An n-channel transistor acts as a simple differential amplifier. This is because the current at the drain of each transistor is the same magnitude, and each goo1 is at the same potential.

Therefore, the current through each transistor should be the same. Therefore, the voltages at the sources of transistors 7.9 are forced to be equal. At this time, the voltage forcibly applied to Vss from these equal voltage sources of transistor 7.9 should be a diode voltage, since diode 11 does not receive this voltage. Therefore, since the voltage across resistor 13 is known and its resistance value is known, the current flowing through it is also known.

FIG. 2 shows a preferred embodiment circuit utilizing the present invention and the necessary starting circuitry. In this circuit, the transistor 3.5 of FIG. 1 is replaced by two sets of p-channel transistors 21.23 and 25.27. Furthermore, instead of the device 7.9 of FIG. 1, two sets of n
Channel i ~ transistors 29.31 and 33.35
is used. Diode 11 in FIG. 1 has been replaced by a diode-connected pnpt-transistor 37, and resistor 13 in FIG. 1 is shown as three resistors of the same type as shown in FIG.

For the circuit of Figure 1, and also for the portions mentioned above of the circuit of Figure 2, zero current flow is a stable operating condition, ensuring that there is actually a reference current in the circuit. For this purpose, it is necessary to install a starting circuit. This starting circuit consists of p-channel transistor M1. M2.
M3 and capacitor C1. Transistors M1 and M3 are connected in series between Vdd and Vss, with the gates of transistor M1 coupled to the gates of transistors 21 and 23, and the gate of transistor M3 coupled to its drain, which is also at Vss.

Transistor M2 is at Vdd, transistors 25, 29
, and its gate is coupled to the connection point of transistors M1 and M3. The starter circuit initially forces current into the reference circuit, then shuts down and is disconnected from the circuit.

To explain the operation, when a S voltage of Vdd is applied to the circuit, as the voltage of the circuit increases, the transistor 21.23.25.27.29.3
There is no current flowing through 1.33.35.

Therefore, transistor M1 is turned off, but transistor M3 is on and acts as a large resistor. Therefore, as Vdd continues to increase relative to Vss, the gate of transistor M2 remains near Vss due to the resistive action of transistor M3. Capacitor C1
but ■ S of Vdd with respect to V under rapid transient conditions, the gate of transistor M2
Helps keep it close to ss. vdd is p with respect to Vss
When the channel Vt is reached, transistor M2 turns on and begins charging the gate of transistor 29.31. The voltage across the circuit is two p-channel ■S
When the sum of the at voltage drop, the two n-channel Vt voltage drops, and the diode voltage drop is reached (this is the voltage drop across transistors 21, 25, 29, 33, 37, i.e. about 2. 5), current begins to flow and a diode voltage value is applied across the three resistors. When transistor M2 turns on, it forces current into the node at the connection point of transistor 29.33;
Pulling up the drain voltage of the n-channel devices 29, 33 thus turns off these transistors as soon as their diode breakdown voltage is reached, since they are connected as diodes. As a result, current is applied to the gates of the transistors 31 and 35, so a current flows through the resistor 39. This current flows to the upper mirror (1
~ Returning to transistors 21.23, 25.27>, the L side mirror transistor is turned on, and due to the current mirror effect (gate-source voltages are equal), 1
The current in transistor M1, which is a ratio of the current in transistor 23, also turns on transistor M1. This pulls the voltage on the gate of transistor M2 upward, turning transistor M2 off. Therefore, transistor M2 no longer injects current into the current reference circuit from the junction of transistors 25, 29, and the reference circuit now operates at the reference current level. This level is stable and requires no further monitoring.

When using this current source to bias the amplifier, do we have transistor 41? Transistor 23 in IJiE mirror
Use the ratio of the current. Transistor 41 is connected in cascode using transistor 43 to increase the output impedance.

It will be appreciated that a current reference circuit has been provided that is simple in design, economical, and temperature independent, independent of the voltage across it.

Although the invention has been described with respect to certain preferred embodiments,
Various modifications will readily occur to those skilled in the art. Accordingly, the claims should be interpreted as broadly as possible in light of the prior art to encompass such modifications.

In connection with the above description, the following sections are further disclosed.

(1) A semiconductor diode coupled to a reference voltage source, the voltage drop across which has a negative temperature dependence, and a negative temperature coefficient of resistance that matches the temperature dependent voltage drop across the diode. a resistor coupled to said reference source, and means for applying substantially the same voltage across both said diode and said resistor with respect to said reference source; Unrelated current reference circuit.

(2) In the temperature-independent current reference circuit described in (1), a pair of p-channel transistors, each stage for applying current coupled to a voltage source; and a pair of n-channel transistors coupled between the diode and the resistor to form a pair of parallel circuits, each parallel circuit comprising one p-channel transistor and one n-channel transistor. A temperature independent current reference circuit including a transistor and one of said diode and resistor.

(3) In a temperature-independent current reference circuit as described in paragraph (1), the temperature-independent current reference circuit includes starting circuit means for initiating current flow through the reference circuit in response to a predetermined voltage. .

(4) In a temperature-independent current reference circuit described in paragraph (2), the temperature-independent current reference circuit includes starting circuit means for initiating current flow through the reference circuit in response to a predetermined voltage. .

(5) In the temperature-independent current reference circuit described in paragraph (1), the means for applying current is connected to a first pair of p-channel transistors, both of which are coupled to a voltage source. a second pair of p-channel transistors also coupled to different ones of the first pair of p-channel transistors; and a second pair of p-channel transistors of the second pair of p-channel transistors. a first pair of n-channel transistors coupled to different ones; a second pair of n-channel transistors;
a pair of n-channel transistors, each second n-channel transistor coupled between a different first n-channel transistor and a different one of the diode and the resistor. Temperature independent current reference circuit.

(6) In the temperature-independent current reference circuit described in paragraph (3), the means for applying current is connected to a first pair of p-channel transistors, both of which are coupled to a voltage source. a second pair of p-channel transistors also coupled to different ones of the first pair of p-channel transistors; and a second pair of p-channel transistors of the second pair of p-channel transistors. a first pair of n-channel transistors coupled to different ones; a second pair of n-channel transistors;
a pair of n-channel transistors, each second n-channel transistor having a different first
a temperature independent current reference circuit coupled between an n-channel transistor of and a different one of said diode and resistor.

(7) In the temperature independent current reference circuit described in paragraph (1), the resistor is doped to a predetermined doping level and is formed of 1=polysilicon.

(8) In the temperature independent current reference circuit described in paragraph (2), the resistor is formed of polysilicon doped to a predetermined doping level.

(9) In the temperature independent current reference circuit described in paragraph (3), the resistor is formed of polysilicon doped to a predetermined doping level.

(10) In the temperature independent current reference circuit described in paragraph (4), the resistor is formed of polysilicon doped to a predetermined doping level.

(11) A temperature independent current reference circuit according to paragraph (5), wherein the resistor is formed of polysilicon doped to a predetermined doping level.

(12) In the humidity independent current reference circuit described in paragraph (6), the temperature independent current reference circuit wherein the resistor is formed of polysilicon doped to a predetermined doping level.

(13) A temperature-independent current reference circuit that is independent of the voltage across the circuit is connected across the semiconductor diode (37);
A polysilicon resistor (3
9) includes a circuit that applies substantially the same voltage to both ends of the circuit. The resistor (39) is doped to have a negative temperature coefficient of resistance, such that the change in its resistance substantially balances the change in voltage drop across the diode (37) due to temperature changes, thereby increasing the resistance. The current through (39) is −
・Stays constant.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a simple temperature compensation circuit according to the present invention.
FIG. 2 is a circuit diagram of a current reference source according to a preferred embodiment of the invention. Explanation of main symbols dd, VS,: Voltage source 11: Diode 13: Resistor

Claims (1)

[Claims] (1) A semiconductor diode coupled to a reference voltage source, across which the voltage drop F has a negative temperature dependence, and a negative temperature coefficient of resistance that matches the temperature dependent voltage drop across the diode. a resistor for generating a substantially constant current, independent of temperature, having a resistor coupled to said reference source, and means for applying substantially the same voltage across both said diode and said resistor with respect to said reference source. current reference circuit.