JP2006222889A - Transmission circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission circuit that can suppress the effect of an increase in current by an overinput on an element for amplification. <P>SOLUTION: The transmission circuit comprises: a power amplifier circuit 30 which has a transistor 33 for amplification for amplifying a transmission signal entered to an input terminal 31 and outputting the transmission signal to an output terminal 35 and has a direct current bias supplied to the input terminal 31 of the transistor 33 for amplification; and a protective circuit 40 which has an overcurrent protective transistor 45 connected between the input terminal 31 of the transistor 33 for amplification and ground and uses a parallel resonance circuit 43 connected to the output terminal 35 of the power amplifier circuit 30 to place the overcurrent protective transistor 45 in a high resistance state when power detected by selecting a frequency from output voltage of the transmission signal of the transistor 33 for amplification is not higher than a prescribed value and the overcurrent protective transistor 45 in a low resistance state when the detected power exceeds the prescribed value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transmission circuit used in a terminal such as a mobile phone or an information communication device or a base station.

  In recent years, the communication performed by information communication devices such as mobile phones has increased in capacity and has spread widely in daily life. The increase in communication capacity is realized by increasing the speed of components used in communication equipment, increasing the storage capacity, and the like. The increase in communication capacity can provide multi-functionality and ease of use. However, the penetration into daily life is an element that cannot be overlooked in that reliability and stability are further improved. In other words, the circuits and components used in these information communication devices need to be highly reliable to cope with long-term continuous use and various conceivable situations. In particular, transmission circuits including power amplifier circuits that constitute the main components of information communication equipment are required to be able to communicate stably without being easily broken in various situations in addition to supporting high speed. Yes.

  In a mobile phone or the like, the power output from the antenna must not exceed the standard, and is often adjusted by the input power supplied to the amplifying element of the power amplifier circuit. For example, an AGC (Automatic Gain Control) amplifier arranged at the front stage of the power amplifier circuit has its function. That is, in the transmission circuit, a part of transmission power output from the power amplification circuit is detected by the power detection circuit, diode detection is performed, and the detection signal is transferred to the APC (Automatic Power Control) control unit of the control signal detection circuit. The APC control unit recognizes the transmission power, and if it deviates from the transmission power, adjusts the input to the amplifying element with an AGC amplifier to optimize the transmission power (see, for example, Patent Document 1).

  In this conventional transmission circuit, control is performed so that excessive current does not flow through the amplifying element in many situations. That is, the power detection circuit and the control signal detection circuit play a certain role as a protection circuit in the transmission circuit without applying excessive input to the amplification element of the power amplification circuit. However, when an abnormality occurs in the power detection circuit, the control signal detection circuit, etc., for example, when the detection diode of the power detection circuit is broken, the input to the amplifying element is made via the AGC amplifier. There is a problem that it cannot be controlled and the amplifying element is destroyed.

  In this conventional transmission circuit, the following steps are taken from detection of excessive transmission power to control of the input current to the amplifying element. The step of detecting the voltage level of the carrier wave output by the power detection circuit, the comparison step of comparing this voltage level with the reference voltage in the APC control unit of the control signal detection circuit, and the control so that the input power is instructed by the AGC amplifier In addition, many steps such as a step of suppressing an input current to the amplifying element through a band-pass filter (BPF) are necessary. For this reason, a current due to excessive input flows through the amplifying element until excessive output power is detected and the input current of the amplifying element is suppressed, and the possibility of performance deterioration of the amplifying element increases.

Therefore, it is possible to detect a situation in which excessive power is generated in the power amplifying circuit, that is, a circuit that can promptly prevent destruction of the amplifying element without going through a control circuit that requires many steps. Thus, there is a strong demand for adding a circuit that protects the amplifying element by suppressing the input current to the amplifying element as quickly as possible.
JP-A-8-204587 (page 4, FIG. 19)

  The present invention provides a transmission circuit capable of suppressing the influence of an increase in current due to excessive input on an amplifying element.

  A transmission circuit according to one aspect of the present invention includes a power amplifying circuit including an amplifying element that amplifies a transmission signal input to an input terminal and outputs the amplified signal to an output terminal, and a DC bias supplied to the input terminal of the amplifying element. And an output power of the transmission signal of the amplifying element by frequency selection detecting means connected to the output end of the power amplifying circuit, and having a current path connected between the input terminal of the amplifying element and the ground When the power detected by selecting the frequency from is less than a predetermined value, the current path is set to a high resistance state, and when the detected power exceeds a predetermined value, the current path is set to a low resistance state. And a protective circuit.

  ADVANTAGE OF THE INVENTION According to this invention, the transmission circuit which can suppress the influence which the increase in the electric current by overinput has on the element for amplification can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. In the figure shown below, the same code | symbol is attached | subjected to the same component.

  A transmission circuit according to Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram schematically showing a transmission circuit, and FIG. 2 is a circuit diagram of a high-frequency power amplification circuit and a protection circuit in the transmission circuit.

  As shown in FIG. 1, the transmission circuit 1 corresponds to a part of a transmission circuit of a mobile phone, for example. The transmission circuit 1 protects the power amplification circuit 30 in the direction in which the transmission signal travels, an IFIC (Intermediate Frequency Integral Circuit) 12, an AGC amplifier 13 as a driver amplifier, a band-pass filter 14, a power amplification circuit 30 having an amplification element. A circuit 40 and an isolator 18 are included. The output power of the power amplifier circuit 30 is sent from the output terminal 19 to the antenna (not shown) side via the isolator 18.

  On the other hand, the output power of the power amplifier circuit 30 is detected by the power detection circuit 21 via the coupler 17 connected to the output terminal of the power amplifier circuit 30 and, for example, diode-detected. This detection signal is transferred to an APC (Automatic Power Control) control unit of the control signal detection circuit 23. The APC control unit recognizes the transmission power. If the transmission signal is different from the transmission power, the input to the power amplifier circuit 30 is AGC ( Automatic gain control) The transmission power is optimized by adjusting the amplifier 13. Note that a power supply circuit and the like are omitted from the transmission circuit 1. Further, the AGC amplifier 13 may be disposed in the IFIC 12.

  The first embodiment is characterized in that a protection circuit 40 is added to the power amplifier circuit 30 in the transmission circuit 1 described above.

  Next, the protection circuit 40 will be described together with the power amplifier circuit 30. As shown in FIG. 2, the power amplifier circuit 30 includes an amplifying transistor 33 made of, for example, a GaAs bipolar transistor that is a high-frequency amplifying element. The base that is the input terminal of the amplifying transistor 33 is connected to the input terminal 31 via a DC cut capacitor 32 that removes a DC component. A DC bias circuit 36 that supplies a DC bias that is an operating current is connected to the base of the amplifying transistor 33 via a choke resistor 37.

  The collector of the amplifying transistor 33 corresponds to the output terminal, and a collector bias 38 is connected to the collector, and the collector is connected to the output terminal 35 via the DC cut capacitor 34. The emitter of the amplifying transistor 33 is grounded. In the power amplifier circuit 30, the input / output matching circuit is omitted. In the present embodiment, the power amplifying circuit 30 including the one-stage amplifying transistor 33 is shown. However, an amplifying transistor configuration including a plurality of stages, for example, an initial stage, a middle stage, and a final stage may be used. The element is not limited to a bipolar transistor, and may be a field effect transistor or the like. Further, the transistor is not limited to GaAs, but may be Si-based, SiGe-based, or a compound-based transistor such as InP-based or GaN-based.

  The protection circuit 40 includes an overcurrent protection transistor 45 formed of a GaAs bipolar transistor that forms a current path, a parallel resonance circuit 43 including a resonance inductor 41 and a resonance capacitor 42 as frequency selection detection means, a DC cut capacitor 44, and a control bias. 47. The overcurrent protection transistor 45 is not limited to a GaAs type, and may be a Si type or other compound type transistor, or may be a field effect transistor or the like without being limited to a bipolar transistor.

  The collector of the overcurrent protection transistor 45 is connected to the base of the amplification transistor 33, and the emitter of the overcurrent protection transistor 45 is grounded.

  One end of the parallel resonant circuit 43 is connected to the collector of the amplifying transistor 33, and the other end is connected to the base of the overcurrent protection transistor 45 via the DC cut capacitor 44. The DC control bias 47 is connected to the base of the overcurrent protection transistor 45.

  In this parallel resonance circuit 43, the resonance inductor 41 and the resonance capacitor 42 are adjusted so that the fundamental frequency of the carrier wave of the transmission signal has a resonance frequency. Accordingly, the parallel resonant circuit 43 is in a high impedance state with respect to the fundamental frequency, but is in a low impedance state with respect to frequencies other than the fundamental frequency, and outputs power other than the fundamental frequency, that is, harmonic components of the carrier wave. The main output power is selectively detected. A voltage in which the detected harmonic component is dominant is applied to the base of the overcurrent protection transistor 45.

  The characteristics of the amplifying transistor 33 until deterioration or destruction due to excessive input can be obtained in advance. That is, the output power of the carrier fundamental frequency and the output power other than the fundamental frequency associated therewith are determined by actual measurement or simulation when it is determined that an excessive load is applied due to excessive input and abrupt degradation occurs. Based on the result, the limit value of the detection voltage based on the output power other than the fundamental frequency necessary for protecting the amplifying transistor 33 can be determined.

  The control bias 47 is set so that the current path of the overcurrent protection transistor 45 is surely turned on when the amplifying transistor 33 operates abnormally and a limit value of the detected voltage is added. Conversely, even if the control bias 47 is applied to the base of the overcurrent protection transistor 45 by adding a voltage obtained from the parallel resonance circuit 43 to the control bias 47 when the amplifying transistor 33 is operating normally, The voltage is set so that the current path of the protection transistor 45 does not become conductive.

  Since the control bias 47 depends on the characteristics of the overcurrent protection transistor 45, it cannot be determined unconditionally, but can be set to about 1.1 V, for example. The control bias 47 may be supplied from the collector bias 38 or the DC bias circuit 36 by resistance voltage division, or may be supplied as a separate power source.

  Next, the operation of the protection circuit 40 will be described. As shown in FIG. 2, the parallel resonant circuit 43 connected between the collector of the amplifying transistor 33 and the DC cut capacitor 44 has a ratio that increases as the degree of over-input increases with respect to the fundamental frequency output power of the carrier wave. Output power at a frequency other than the fundamental frequency whose main component is a rising harmonic component is detected. The power in which the detected harmonic component is dominant is applied to the control bias 47 applied from the outside and applied to the base of the overcurrent protection transistor 45. In addition, since the parallel resonant circuit 43 is in a high impedance state with respect to the fundamental frequency, it does not substantially affect the fundamental frequency output power.

  When the amplifying transistor 33 is operating normally, the voltage applied to the base of the overcurrent protection transistor 45 does not make the current path of the overcurrent protection transistor 45 conductive. During this period, no current flows and the current path is closed.

  On the other hand, when an excessive input current is input to the amplifying transistor 33 and an excessive carrier output power is output, the voltage applied to the base of the overcurrent protection transistor 45 is in a conductive state in the current path of the overcurrent protection transistor 45. To. The mechanism for bringing the current path into a conductive state is rectified by a portion corresponding to a diode between the base and the emitter of the overcurrent protection transistor 45, and raises the DC bias point of the base of the overcurrent protection transistor 45. The 45 collector and emitter become conductive. As a result, the base of the amplifying transistor 33 opens the current path with respect to the ground, and the voltage decreases. The amplifying transistor 33 is substantially in a non-operational state, an excessively loaded state is eliminated, and it can be protected without causing performance degradation or destruction.

  Since the detection of the output power at a frequency other than the fundamental frequency to the drop of the base potential of the amplifying transistor 33 can be performed in one step, that is, the operation of the overcurrent protection transistor 45, the input is made through several steps in the past. The operation of the amplifying transistor 33 can be stopped more quickly than when the current is adjusted. In addition, since a part of the output power of the carrier wave is not detected, it is not necessary to add that amount to the output power of the amplifying transistor 33 in advance.

  Therefore, the protection circuit 40 according to the present embodiment can provide the transmission circuit 1 capable of minimizing the influence of an increase in current due to excessive input on the power amplification circuit 30 including the amplification transistor 33. .

  The protection circuit 40 is added to the transmission circuit 1 having a circuit for optimizing the output power by the power detection circuit 21 and the control signal detection circuit 23, so that the protection circuit 40 is independent of the power detection circuit 21 and the control signal detection circuit 23. Thus, the power amplifier circuit 30 can be protected. As a result, the transmission circuit 1 can be made more reliable, and more stable communication can be performed in a mobile phone or the like.

  A transmission circuit according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 3 is a circuit diagram of a high frequency power amplifier circuit and a protection circuit in the transmission circuit. The difference from the transmission circuit of the first embodiment is that the series resonance circuit 53 is adopted for the protection circuit 40. In addition, the same code | symbol is attached | subjected to the same component as Example 1, and description of an overlapping part is abbreviate | omitted.

  As shown in FIG. 3, the protection circuit 50 according to the second embodiment includes an overcurrent protection transistor 45 that is a current path, a series resonance circuit 53 that includes a resonance inductor 51 and a resonance capacitor 52 that are frequency selection detection means, and A control bias 47 is used.

  The collector of the overcurrent protection transistor 45 is connected to the base of the amplification transistor 33, and the emitter of the overcurrent protection transistor 45 is grounded. One end of the series resonance circuit 53 is connected to the collector of the amplifying transistor 33, and the other end is connected to the base of the overcurrent protection transistor 45.

  In this series resonance circuit 53, the resonance inductor 51 and the resonance capacitor 52 are adjusted so as to have a resonance frequency at a second harmonic having a frequency twice the fundamental frequency of the carrier wave of the transmission signal. Accordingly, the series resonant circuit 53 is in a low impedance state for the second harmonic, but is in a high impedance state for frequencies other than the second harmonic, and selectively outputs the output power of the second harmonic. Will be detected. The detected second harmonic voltage is applied to the base of the overcurrent protection transistor 45.

  Next, the operation of the protection circuit 50 will be described. As shown in FIG. 3, the ratio of the series resonant circuit 53 connected between the collector of the amplifying transistor 33 and the DC cut capacitor 34 increases as the degree of excessive input increases with respect to the fundamental frequency output power. Detect double harmonics. The detected voltage is applied to the control bias 47 applied from the outside and applied to the base of the overcurrent protection transistor 45. Although the series resonant circuit 53 is in a high impedance state with respect to the fundamental frequency, it appears as a circuit component having an impedance with respect to the carrier wave of the fundamental frequency. It is necessary to match the impedance on the output side of the.

  Although the second harmonic is selectively detected from the first embodiment, the current path of the overcurrent protection transistor 45 can be operated by the same mechanism as the first embodiment. As a result, when an excessive input current is input to the amplifying transistor 33 and an excessive carrier wave output power is output, the amplifying transistor 33 can be promptly substantially deactivated. Can be protected without causing performance degradation or destruction.

  As described above, in the present embodiment, the same effect as that obtained in the first embodiment can be obtained. In addition, since the DC cut capacitor 43 required in the first embodiment uses the series resonance circuit 53, it is not necessary in the present embodiment.

  A transmission circuit according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 4 is a circuit diagram of a high frequency power amplifier circuit and a protection circuit in the transmission circuit. The difference from the transmission circuit 1 of the first or second embodiment is that a short stub having a quarter wavelength of the fundamental wave of the carrier wave is used for the protection circuit 40 or 50. In addition, the same code | symbol is attached | subjected to the same component as Example 1 or 2, and the description is abbreviate | omitted.

  As shown in FIG. 4, the protection circuit 60 of this embodiment includes an overcurrent protection transistor 45 as a current path, a quarter wavelength short stub 61 as a frequency selection detection means, a DC cut capacitor 44, a control bias 47, And a high frequency grounding capacitor 64.

  The collector of the overcurrent protection transistor 45 is connected to the base of the amplification transistor 33, and the emitter of the overcurrent protection transistor 45 is grounded. One end of the quarter-wave short stub 61 is connected to the collector of the amplifying transistor 33, the other end is grounded via the high-frequency grounding capacitor 64, and its bisection point is passed through the DC cut capacitor 43. The current protection transistor 45 is connected to the base. The short stub 61 is divided into a short stub 61a connected to the collector of the amplifying transistor 33 and a grounded short stub 61b having a length corresponding to 1/8 wavelength across the bisector.

  The short stub 61 is composed of a microstrip line, and its length is n / 4 times the wavelength (n is an odd number) with respect to the carrier wave of the transmission signal. Circuit. The short stub 61 functions as a bandpass filter. For example, by setting the length of the short stub 61 to ¼ wavelength of the fundamental wave of the carrier wave, the fundamental frequency component of the carrier wave is output without flowing to the short stub 61. It is transmitted to the terminal 35. On the other hand, components other than the fundamental frequency of the carrier wave can flow to the short stub 61, and the second harmonic is efficiently taken out at the bisection point, and the overcurrent protection transistor 45 is passed through the DC cut capacitor 44. Applied to the base.

  Next, the operation of the protection circuit 60 will be described. As shown in FIG. 4, the short stub 61 connected between the collector of the amplifying transistor 33 and the DC cut capacitor 44 has a degree of excessive input with respect to the fundamental frequency output power at the bisection point. The second harmonic whose ratio increases is detected. The detected second harmonic voltage is applied to an externally applied control bias 47 and applied to the base of the overcurrent protection transistor 45. In addition, since the short stub 61 having a quarter wavelength of the fundamental wave is in a high impedance state with respect to the fundamental frequency, the fundamental frequency output power is not substantially affected.

  The second embodiment is different from the second embodiment in that the second harmonic is detected using the quarter wavelength short stub 61, but the current path of the overcurrent protection transistor 45 is the same mechanism as in the first or second embodiment. It is possible to operate with. As a result, when an excessive input current is input to the amplifying transistor 33 and an excessive carrier wave output power is output, the amplifying transistor 33 can be promptly substantially deactivated. Can be protected without causing performance degradation or destruction.

  As described above, in the present embodiment, the same effect as that obtained in the first embodiment can be obtained. In addition, the DC cut capacitor 43 which is unnecessary in the second embodiment is necessary in the present embodiment, but affects the impedance matching on the transmission output side of the power amplifier circuit 30 with respect to the fundamental frequency of the carrier wave. Therefore, the design load is reduced as compared with the series resonant circuit of the second embodiment.

  As mentioned above, this invention is not limited to the said Example, In the range which does not deviate from the summary of this invention, it can change and implement variously.

  For example, in the above-described embodiment, a power amplifier circuit configured by a single stage amplification transistor is shown, and a power amplifier circuit configured by a plurality of stages, for example, a first stage, a middle stage, and a final stage may be used. Stated. In the case of a multi-stage configuration, the output power of the final stage is detected, and a current path such as an overcurrent protection transistor controlled based on the detected voltage is connected to the transmission signal input terminal of the first stage amplification transistor. It can be a circuit.

  In addition, since the protection circuit of the above embodiment detects the output power of the power amplifier circuit and suppresses the input current of the power amplifier circuit, it is not affected by circuits other than the power amplifier circuit to which the protection circuit is added. . Therefore, it is easy to apply to other than the illustrated transmission circuit.

1 is a block diagram schematically showing a transmission circuit according to Embodiment 1 of the present invention. 1 is a circuit diagram of a high-frequency power amplifier circuit and a protection circuit in a transmission circuit according to Embodiment 1 of the present invention. FIG. 6 is a circuit diagram of a high-frequency power amplifier circuit and a protection circuit in a transmission circuit according to Embodiment 2 of the present invention. FIG. 6 is a circuit diagram of a high-frequency power amplifier circuit and a protection circuit in a transmission circuit according to Embodiment 3 of the present invention.

Explanation of symbols

1 Transmitter circuit 11, 31 Input terminal 12 IFIC
13 AGC amplifier 14 Band pass filter 17 Coupler 18 Isolator 19, 35 Output terminal 21 Power detection circuit 23 Control conversion circuit 30 Power amplification circuit 32, 34, 44 DC cut capacitor 33 Amplifying transistor 36 DC bias circuit 37 Choke resistor 38 Collector Bias 40, 50, 60 Protection circuit 41, 51 Resonance inductor 42, 52 Resonance capacitor 43 Parallel resonance circuit 45 Overcurrent protection transistor 47 Control bias 53 Series resonance circuit 61, 61a, 61b Short stub 64 High frequency grounding capacitor

Claims (5)

A power amplifying circuit having an amplifying element that amplifies a transmission signal input to the input end and outputs the amplified signal to an output end, and a DC bias supplied to the input end of the amplifying element;
A frequency selection detecting means having a current path connected between the input terminal of the amplifying element and the ground, and connected to the output terminal of the power amplifier circuit, generates a frequency from the output power of the transmission signal of the amplifying element. When the selected and detected power is below a predetermined value, the current path is set to a high resistance state, and when the detected power exceeds a predetermined value, the current path is set to a low resistance state. Circuit,
A transmission circuit comprising:   The transmission circuit according to claim 1, wherein the input terminal is a base of a bipolar transistor or a gate of a field effect transistor.   The frequency selection detection means detects other frequency components excluding the carrier fundamental frequency, or detects a frequency component that is an integral multiple of the fundamental frequency excluding the carrier fundamental frequency. Transmitter circuit.   The frequency selection detecting means is constituted by a resonant circuit including an inductor and a capacitor, or a circuit using a short stub having a length of n / 4 times (n is an odd number) of the wavelength of a carrier wave consisting of a microstrip line. The transmission circuit according to any one of claims 1 to 3, wherein the transmission circuit is characterized in that:   The current path of the protection circuit is a bipolar transistor in which a collector is connected to the base of the amplifying element, an emitter is connected to ground, and a base is connected to the frequency selection detecting means, or one of a source and a drain is the base of the amplifying element. And a control bias for supplying a predetermined voltage to the base of the bipolar transistor or the gate of the field effect transistor, the field effect transistor having the other of the source and drain connected to the ground and the gate connected to the frequency selection detecting means. The transmission circuit according to claim 1, wherein the transmission circuit is connected.

Images