KR100834691B1 - Over voltage protection circuit for rf ic - Google Patents

Abstract

An over voltage protection circuit for an RFIC(Radio Frequency Integrated Circuit) is provided to reduce power consumption by consuming small current in an inactivation. An RFIC includes a first transistor(130) and first and second bias resistors(140,150). An over voltage protection circuit(300) for the RFIC includes a second transistor(310) and an operation voltage determining unit. The second transistor blocks over current introduced into the RFIC according to voltage supplied from the outside. The operation voltage determining unit determines operation voltage of the second transistor by dividing the supplied voltage. The second transistor is turned on/off according to operation voltage applied to a second base terminal(312) by including a signal input terminal, a second collector terminal(311), a second emitter terminal(313), and the second base terminal. The second collector terminal is connected to a base terminal of the first transistor. The second emitter terminal is connected to a ground terminal. The second base terminal receives the operation voltage of the second transistor.

Description

Overvoltage Protection Circuit for RFC IC {Over Voltage Protection Circuit for RF IC}

The present invention relates to an overvoltage protection circuit for an RF IC, and more particularly, to overvoltage protection for an RF IC to improve the ruggedness of the RF IC device against abnormal overcurrent inflow by coupling the overvoltage protection circuit to the RF IC device. It is about a circuit.

Recently, the number of users of electronic devices using the resources of the RF band is gradually increasing. That is, electronic devices using frequency resources of RF bands, such as portable terminals, RF ID equipment, and mobile communication terminals, provide a lot of convenience to users.

Furthermore, since these electronic devices are becoming more compact and multifunctional, the utility of RF IC devices is further increased. Therefore, the driving voltage of such an RF IC element is gradually lowered, but is vulnerable to fluctuations in input power or static electricity, which generate a high current instantaneously.

1 is an equivalent circuit of a simplified RF IC. As shown in the drawing, the RF IC 100 includes an input signal and a first collector terminal 131 connected to a supply voltage terminal 110 and an output signal terminal 160. A first transistor 130 having a first base 133 connected to the terminal 120 and a first emitter terminal 132 connected to the ground terminal; And a first bias resistor 140 connected to the supply voltage terminal 110 and the first base 133 terminal, the first base 133 terminal, and a ground to provide a bias voltage of the first transistor. And a second bias resistor 150 connected to it.

The RF IC 100 has a current Icc flowing into the first collector terminal 131 of the first transistor 130 at two bias resistors 140 and 150 (R1 and R2) and a supply voltage terminal 110. It is configured to be determined by the supplied supply voltage (Vcc) When the supply voltage (Vcc) is changed, the first collector current (Icc) also changes in conjunction, the first collector current (Icc) is a supply voltage (Vcc) Exponentially

Fig. 2 is a characteristic curve of current with respect to the voltage of an RF IC which does not employ the overvoltage protection circuit according to the prior art. Referring to Fig. 2, the solid line is a current-voltage characteristic curve through simulation, and the dotted line shows the maximum current that can be allowed in the state in which the RF IC device can be normally operated. The RF IC device used in this experiment is designed to operate normally at 5V / 100mA below the maximum current. From FIG. 2, it can be seen that the RF IC device may thermally damage part or all of the device when a current of 200 mA or more flows, and may not operate normally even if the overcurrent introduced into the overvoltage cutoff disappears.

The current Ice flowing into the first transistor through the first collector terminal by the supply voltage is determined by the following equation.

In other words, Vbe1 = Vcc * R1 / (R1 + R2) ------------------------------------- --(One)

    Ice ≒ exp (Vbe1 / KT) --------------------------------------- (2)

Where Vbe1 is the base voltage of the first transistor, Vcc is the external supply voltage, R1 and R2 are the first and second bias resistors, and Ice is the first collector current.

Therefore, it should be noted that the first collector current Is flowing into the first transistor 130 changes to an exponential function according to the change of the external supply voltage Vcc.

3 is an example of a general application circuit used in an RF IC. Referring to FIG. 3, the inductor 221 (L1) separates a DC signal from a radio frequency (RF) signal and functions to separate an output terminal and an input terminal from a high frequency signal.

A plurality of capacitors (222, 223, 224) (C3, C4, C5) connected between the supply voltage terminal 220 (Vcc) and the inductor 221 is generated by an external power source, and the high frequency noise introduced into the RF IC element. By-pass capacitor to remove the (by). Zener diode 225 (Zd) protects the RF IC from high voltage spikes or surge voltages generated from an external power supply (Vcc).

When the zener diode 225 is induced with a voltage higher than the rated voltage, the zener diode 225 becomes a low resistance state and serves as a path for flowing the overcurrent caused by the induced high voltage to ground, thereby protecting the peripheral device from a voltage higher than the rated voltage. Do it. In some cases, instead of the zener diode, it is possible to connect a high-capacity tantalum capacitor between the external power supply Vcc and the ground. The high capacitance (2-10uF) tantalum capacitor protects the RF IC by emitting high voltage surges or spikes generated from an external power source to ground before entering the RF IC through the inductor 221. .

For example, if the RF IC device is designed to operate normally under a voltage current of 5 V / 100 mA or less, permanent current damage may occur when a current of 200 mA or more flows through the RF IC device. As shown in Equations (1) and (2), the current flowing through the RF IC is determined by the voltage induced at the external power supply (Vcc) terminal. Under normal conditions, a voltage of 5V is applied to the external power supply terminal, but in some cases it can take more than 5V.

When the power is turned on and off, when voltage spikes or surges occur, when overvoltage is supplied from an external power supply terminal, when the output terminal 230 is momentarily shorted to ground, RF Situations may occur where abnormal overcurrent may flow into the IC device.

As described above, the conventional protection method is not preferable in terms of space and economics because a large capacity capacitor or zener diode should be used.

In addition, since the surge voltage or voltage spike generated at the output terminal directly enters the RF IC without passing through the inductor 221, the inductor 221 or the plurality of capacitors 222, 223, and 224 also have high voltage spikes generated at the output terminal. There is a problem in that the RF IC is not protected from spikes or surges.

The present invention has been proposed to solve the above problems, and the present invention is to protect the RF IC by blocking the abnormal over-current flowing into the RF IC due to instantaneous or continuous overvoltage by combining an overvoltage protection circuit to the RF IC There is this.

In addition, the purpose is to protect the RF IC by blocking abnormal over-current flowing into the RF IC due to problems such as high voltage surge or spike generated in the output terminal.

In order to achieve the above object, the overvoltage protection circuit for an RF IC according to the present invention is a RF IC device including a first transistor and a first and second bias resistors, the RF IC according to the magnitude of the external supply voltage And a second transistor for blocking an overcurrent flowing into the circuit, and an operating voltage determiner configured to divide the supply voltage and determine an operating voltage of the second transistor.

The second transistor includes a signal input terminal, a second collector terminal connected to the base terminal of the first transistor, a second emitter terminal connected to a ground terminal, and a second base terminal to which an operating voltage of the second transistor is applied. And on / off according to the magnitude of the voltage applied to the second base.

The operation voltage determining unit includes a first voltage divider resistor connected between the supply voltage terminal and the second base terminal, and a second voltage divider resistor connected between the second base terminal and the ground terminal.

Here, the first and second voltage divider resistors are three to five times larger than the first and second bias resistors in order to prevent the output of the RF IC from being fed back to the input of the overvoltage protection circuit. It is characterized by having a value.

The operating voltage determiner may further include a capacitor connected in parallel to the second voltage divider resistor so that the RF IC device obtains a low frequency response that converges to a high frequency response.

The capacitor of the overvoltage protection circuit for the RF IC is used to improve low frequency response. The presence or absence of the capacitor does not affect the RF response characteristics at high frequencies of 4 ~ 5 GHz or more, but has a large effect on the RF response characteristics at frequencies below this. That is, the larger the capacitor, the better the RF response at low frequencies.

The second transistor is turned on when the voltage of the second base terminal is higher than a reference voltage to turn off the first transistor. When the voltage is lower than the reference voltage, the second transistor is turned off. It characterized in that (on). In addition, the first and second voltage divider resistors are variable to adjust the reference voltage.

As described above, the present invention protects the device from overvoltages that can be induced in the RF IC device. When an overvoltage is applied from an external power source or a high voltage surge or spike occurs from an output terminal, the overvoltage protection circuit for the RF IC according to the present invention operates to stop the operation of the RF IC device.

In addition, the overvoltage protection circuit for the RF IC according to the present invention is activated when an overvoltage is applied to protect the RF IC by blocking abnormal inflow of overcurrent, and consumes a small amount of current of about 1 mA even when inactive, thereby reducing power consumption. have.

In addition, the overvoltage protection circuit for the RF IC according to the present invention does not affect the radio frequency (RF) response characteristics of the RF IC device since the output impedance when the inactive is 50 times or more than the input impedance of the RF IC device.

Hereinafter, an overvoltage protection circuit for an RF IC according to an embodiment of the present invention will be described in detail with reference to FIGS. 4 to 6.

4 is an additional circuit diagram of an RF IC overvoltage protection circuit for an RF IC according to an embodiment of the present invention.

Referring to FIG. 4, a general RF IC device includes a first collector terminal 131 connected to a supply voltage terminal 110 and an output signal terminal 160, and a first base 132 connected to an input signal terminal 120. And a first transistor 130 having a first emitter terminal 133 connected to a ground terminal, and first and second bias resistors connected to the first base 132 to provide a bias voltage to the first transistor. 140,150).

The RF IC overvoltage protection circuit 300 includes a second transistor 310 and an operating voltage determiner, and includes the first transistor 130 and the first and second bias resistors 140 and 150. Are combined in. The second transistor 310 blocks inflow of abnormal overcurrent flowing into the RF IC device or allows inflow of a normal current according to a magnitude of a supply voltage Vcc, and the operating voltage determining unit sets the supply voltage to the second voltage. The second base terminal 312 is distributed to determine an operating voltage of the second transistor. That is, an input voltage for turning on / off the second transistor is determined.

The second transistor 310 includes an input signal terminal, a second collector terminal 311 connected to the base terminal of the first transistor, a second emitter terminal 313 connected to the ground terminal, and the output. The second base terminal 312 receives a signal and turns on / off the first transistor 130 according to the magnitude of the supply voltage, thereby preventing abnormal overcurrent flowing into the RF IC device. Limit inflow

The operating voltage determiner may include a first voltage distribution resistor 320 connected between the supply voltage terminal 110 and the second base terminal 312 and a second voltage connected between the second base terminal 312 and the ground terminal. It is possible to be composed of two voltage distribution resistor 330.

The first and second voltage distribution resistors 320 and 330 may be configured to prevent the output of the RF IC device from being fed back to the second base terminal 312 for the RF IC. It is desirable to have a resistance value three to five times larger than 140,150).

In addition, by connecting the capacitor 340 to the second voltage divider 330 in parallel, the RF IC device can obtain a low frequency response that converges to a high frequency response. As the capacitance of the capacitor 340 increases, the difference between the output at the low frequency and the output at the high frequency of the overvoltage protection circuit 300 according to the present invention gradually decreases.

The second transistor 310 is turned on when the voltage of the second base terminal is higher than a reference voltage to turn off the first transistor. When the voltage is lower than the reference voltage, the second transistor 310 is turned off and turned off. Turn on the transistor.

In this case, when the supply voltage corresponds to an overvoltage, the second transistor is turned on and the first transistor is turned off, thereby preventing abnormal overcurrent from flowing into the RF IC device.

The reference voltage may be easily adjusted by the first and second voltage divider resistors 320 and 330, and the first and second voltage divider resistors may be configured as variable resistors.

As described above, the state of the second transistor 310 is determined by the voltage of the second base terminal, and the voltage Vbe2 of the second base terminal is calculated by Equation (3) below. The reference voltage Vref is the second base voltage when the supply voltage is less than or equal to the threshold voltages Vcc and crit, and may be determined by Equation 4 below.

Vbe2 = Vcc × R4 / (R3 + R4) -------------------------------- (3)

Vref = Vcc, crit × R4 / (R3 + R4) --------------------------- (4)

Here, Vbe2 is a voltage of the second base terminal, Vcc is a supply voltage applied to the RF IC element, R3 and R4 are resistors for dividing the input voltage of the second transistor, Vref is a reference voltage, and Vcc, crit Is a threshold voltage at which the RF IC element can operate normally.

In general, since the operating voltage (ON voltage) of the transistor is 1.1 to 1.3V, when the operating voltage of the second transistor is 1.2V, the ratio of the first and second voltage distribution resistors R3 and R4 is increased. Can be obtained by Equation (3). Therefore, since the ratio R3 / R4 of the first and second voltage division terms becomes 4.42, if one of the first and second voltage division resistors is arbitrarily determined, the remaining voltage division resistance values are also determined.

Even when the RF IC element is operating normally because the supply voltage is lower than or equal to the threshold voltage, the RF IC overvoltage protection circuit 300 maintains a predetermined idle current Ioff calculated by Equation 5 below. Consume. Therefore, the first and second voltage division resistance values are advantageously large within a range that can be implemented in the RF IC device.

Ioff = Vcc / (R3 + R4) --------------------------------------- (5 )

FIG. 5 is a current-voltage characteristic diagram when there is no overvoltage protection circuit for the RF IC according to the embodiment of the present invention when the threshold voltage is 6.5V.

In FIG. 5, a dotted line shows the current-voltage characteristic when the overvoltage protection circuit for the RF IC is present. The dotted line indicates that although the current flowing into the RF IC device reaches the maximum current due to the increase in the external supply voltage, the current flowing into the RF IC device does not increase the maximum current. This is because the overvoltage protection circuit for the RF IC operates to turn off the first transistor to cut off the current flowing into the RF IC element.

5 is a current-voltage characteristic diagram when there is no overvoltage protection circuit for the RF IC. The solid line indicates that even if the external supply voltage is gradually increased so that the current flowing into the RF IC element is larger than the maximum current, the current inflow cannot be blocked and the inflow current is continuously increasing.

6 is a diagram illustrating a comparison of output characteristics of the RF IC device when the capacitance of the capacitor 340 changes.

Fig. 6 shows the output characteristics when there is no overvoltage protection circuit of the RF IC device according to the present invention (P1dB) and the output characteristics when 5pF and 10pF are used when no capacitor is present in the overvoltage protection circuit of the RF IC device according to the present invention. Shows the result of comparison. As shown in FIG. 6, if the capacitor 340 is not included in the overvoltage protection circuit for the RF IC, the output is greatly reduced at low frequency. However, as the capacitance of the capacitor increases and the frequency increases, the compensation circuit does not modify the characteristics of the original RF IC.

When the overvoltage protection circuit 300 for the RF IC is analyzed in the frequency domain, the second voltage distribution resistor 330 and the capacitor 340 are connected in parallel, and at a low frequency, the impedance of the capacitor 340 Impedance is high. Therefore, when the overvoltage protection circuit for the RF IC handles a low energy signal (small signal), the influence of the capacitor 340 can be ignored. However, when dealing with a high energy signal (large signal), the output cannot be ignored. The signal is fed back to the parallel circuit portion of the second voltage divider resistor 330 and the capacitor 340. Therefore, the capacitor 340 should use a value having a larger capacity as the lowest use frequency is low.

However, when the capacitance of the capacitor 340 is small, the impedance of the capacitor 340 increases in the low frequency band, the gain of the RF IC device is reduced when dealing with a high energy signal.

As described above, although the embodiments of the present invention have been described in detail with reference to the drawings, the spirit and scope of the present invention should not be construed as being limited to the above embodiments, but the scope of the present invention as defined by the appended claims. It will be apparent to those skilled in the art that various modifications are possible within the scope. In addition, the inventors claim that all combinations of the invention described in the claims and the detailed description of the invention are possible and claim the protection of the invention described in the claims.

Figure 1. An equivalent circuit diagram of an RF IC that does not employ a simplified overvoltage protection circuit according to the prior art.

Figure 2. The current-voltage characteristic curve of the RF IC shown in FIG. 1 according to the prior art.

Figure 3. Examples of typical application circuits used in prior art RF ICs.

Figure 4. An overvoltage protection circuit diagram for an RF IC according to an embodiment of the present invention.

Figure 5. Current-voltage characteristic curve of the RF IC device to which the embodiment of the present invention is applied.

Figure 6. Output characteristic diagram for capacitance change of a capacitor applied to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

300: overvoltage protection circuit for RF IC 310: second transistor

311: second collector terminal 312: second base terminal

313: second emitter terminal 320: first voltage divider resistor

330: second voltage divider resistor 340: capacitor

Claims (6)

An RF IC device comprising a first transistor and a first and second bias resistor, A second transistor for blocking an overcurrent flowing into the RF IC device according to the magnitude of an external supply voltage; And an operating voltage determination unit configured to divide the supply voltage and determine an operating voltage of the second transistor. The method of claim 1, The second transistor includes a signal input terminal, a second collector terminal connected to the base terminal of the first transistor, a second emitter terminal connected to a ground terminal, and a second base terminal to which an operating voltage of the second transistor is applied. And on / off according to the magnitude of the voltage applied to the second base terminal. The method of claim 2, The operating voltage determining unit includes a first voltage divider resistor connected between the supply voltage terminal and the second base terminal, and a second voltage divider resistor connected between the second base terminal and a ground terminal. In order to prevent the output of the RF IC from being fed back to the input of the overvoltage protection circuit, the second transistor has three to five times the first and second voltage divider resistors compared to the first and second bias resistors. An overvoltage protection circuit for an RF IC, characterized by having a larger resistance value. The method of claim 3, And the operating voltage determiner further comprises a capacitor connected in parallel to the second voltage divider resistor so that the RF IC element obtains a low frequency response that converges to a high frequency response. The method of claim 3, The second transistor, When the voltage of the second base terminal is higher than the reference voltage is turned on (on) to turn off the first transistor, and when lower than the reference voltage is turned off (off) to turn on the first transistor (on) An overvoltage protection circuit for an RF IC, characterized in that. The method of claim 3, And said first and second voltage divider resistors are variable to adjust a reference voltage.

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