Variable transmission power type transmitter

Abstract: A variable transmission power type transmitter comprises a transmission amplifier (11), a detecting circuit (12) for detection of a transmission wave signal from the transmission amplifier (11), an automatic power control circuit (14) for automatic control of the transmission power of the transmitter amplifier (11) depending on the difference between a set value and a detected output of the detecting circuit (12), a set point pointing circuit (13) for generating set values and for selecting one of the set values to be supplied to the automatic power control circuit (14), and a transmission interruption detecting circuit (15) for detecting existence or absence of the transmission wave signal by comparing the detected output of the detecting means with a reference value. The reference value is automatically generated from one of the set values in the set point providing circuit (13). Therefore, a variable resistor for adjusting the reference value and a adjustment process are not required.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable transmission power type transmitter comprising a transmission interruption detecting circuit. 2. Description of the Related Art In a mobile communication system such as an automobile telephone system, a portable telephone system, and the like, in order to prevent a mobile terminal from transmitting needlessly, and to reduce power consumption of the mobile terminal, the transmission power of the mobile terminal is controlled to be kept as low as possible while maintaining communication when electrical field strength is sufficiently high at the mobile terminal's position, and the transmission power is turned off when transmission is not required. In order to realize these functions, a radio transmitter for a base station and a mobile terminal are provided with an automatic power control circuit (APC circuit) which is capable of variable control of the transmission power. The radio transmitter is also provided with a transmission interruption detecting circuit (or CAR-IND circuit: carrier indicator) for detecting existence or absence of the transmission output, in cooperation with the automatic power control circuit. The radio transmitter is further provided with a set point providing circuit for providing the automatic power control circuit with a set point by which the transmission power of the automatic power control circuit is controlled. The set point providing circuit discretely alters the value of the set point between the values corresponding to a minimum power P min and maximum power P max , according to a command issued from a processor to control the whole apparatus. The transmission interruption detecting circuit compares a detected value of a level of the transmitting power with a predetermined reference value V ref to decide whether the transmission power exists or not. The reference value V ref is manually adjustable to compensate for dispersion of each element. The values corresponding to the P min and P max are also manually adjustable for compensation. In the aforementioned conventional circuit, adjustment of the reference value V ref is required after adjustment of the values corresponding to the P max and the P min . Accordingly, there are so many portions to be adjusted that several production processes are required. Additionally, the scale of the circuit is large and its price is high, since a variable resistor for adjustment of the reference value V ref is required. US-A-4 476 437 discloses a radio transmission system having a negative feedback control loop which produces a DC signal of constant magnitude for automatically setting the output power level to a desired one of a plurality of predetermined power levels. Additionally, an abnormal condition is detected by comparing the DC signal with a predetermined reference signal. A similar kind of system is disclosed in US-A-4 574 248, having a control loop in which a reference signal, derived from an input radio frequency signal, is compared with the radio frequency output, both to control the output power and to enable a fault condition to be detected. A limiter in the control loop causes a constant output power to be produced when the input RF signal exceeds a level set by the limiter. SUMMARY OF THE INVENTION It is an object of the present invention to provide a variable transmission power type transmitter which can be made small in size and at low cost and which can be produced using a simple process without need for adjustment of the reference value V ref whenever an adjustment is made in the values corresponding to P min and P max . According to the invention, there is provided (in common with US-A-4476437, which forms the base for the preamble of claim 1) a variable transmission power type transmitter comprising a transmission amplifier means for outputting a transmission wave signal having variable transmission power, a detection means for detection of a level of the transmission wave signal, an automatic power control means for automatic control of the transmission power of said transmitter amplifier means depending on the difference between a generated value and a detected output of said detecting means, a set point providing means for generating set values and for selecting one of the set values to be supplied as said generated value to said automatic power control means, and a transmission interruption detecting means for detecting existence or absence of the transmission wave signal by comparing the detected output of said detecting means with a reference value generated from one of the set values in said set point providing means. The invention is characterised in that means are provided for simultaneously adjusting all the set values generated by the set point providing means according to selected lower and upper values of the transmission power corresponding to the lowest and highest set values generated by the set point providing means, whereby both said generated value and said reference value are simultaneously adjusted by said level adjusting means according to said selected lower and upper values of the transmission power. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram showing an example of a mobile terminal; Figure 2 is a circuit diagram of a conventional transmitter power variable transmitter; Figure 3 is a diagram showing the characteristics of the transmission power against the set values; Figure 4 is a block diagram of a basic construction of the present invention; and Figure 5 is a circuit diagram of an embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the preferred embodiments according to the invention, examples of aforementioned related art are given with reference to the accompanying drawings. Figure 1 shows a construction of an example of a conventional mobile terminal. A radio wave from a base station (not shown) includes information regarding electric field strength, etc., as well as information regarding an audio signal. A received signal including that information is amplified in a radio receiver 42, transformed into an intermediate frequency signal in a mixer 38 which mixes an input signal with a signal from a local oscillator 40, divided into a signal including audio information and a signal including information on the electrical field strength in band pass filters 36 and 28 to pass signals having corresponding frequencies only, respectively, and demodulated in demodulators 34 and 26, respectively. A microprocessor 24 receives the information regarding the electric field strength, etc., decides on an adequate transmission power, and issues a command toward a set point providing circuit 6′. The set point providing circuit 6′ selects a voltage value from among several predetermined voltage values corresponding to several transmission powers between P max and P min , and supplies the selected voltage value to an automatic power control circuit (APC circuit) 5. The automatic power control circuit 5 and a detecting circuit 2 form a feedback path for a power amplifier circuit 1 to be controlled so that the level of transmission output becomes a value corresponding to the voltage value selected in the set point providing circuit 6′. The microprocessor 24 also controls the ON/OFF of the power amplifier circuit 1 through the automatic power control circuit 5. The transmission output is interrupted when transmission is not required. A transmission interruption detecting circuit (or a carrier indicator) 3′ detects transmission interruption from an output of the detecting circuit 2 and indicates the result on an indicator (not shown). Figure 2 shows detailed constructions of the carrier indicator 3′, the automatic power control circuit 5, and the set point providing circuit 6′ shown in Fig. 1. The detecting circuit 2 detects the level of the transmission wave output to output a corresponding voltage V₁ by AM detection of the transmission wave output. The carrier indicator 3′ compares the voltage V₁ with a predetermined reference voltage V ref to decide whether the transmission power exists or not. A variable resistor 4 is provided for correctly setting the reference voltage V ref , compensating for dispersion of each element. A variable resistor 7 is provided for adjusting transmission power when minimum transmission power P min is selected. A variable resistor 8 is provided for adjusting transmission power when maximum transmission power P max is selected. The carrier indicator 3′ is constructed to include a comparator 31 and resistors 32 to 35. The output of the detecting circuit 2 is input to one of the input terminals of the comparator 31, and the reference voltage V ref which is a voltage divided by a resistor 32 and the variable resister 4 is input to the other input terminal of the comparator 31. The set point providing circuit 6′ is constructed to include a switching circuit 60 and a voltage dividing circuit comprising eight serially connected resistors 61 to 68. Each divided voltage from the voltage dividing circuit is input into one of the input terminals of the switching circuit 60 as set values X₀ to X₇ , respectively. The switching circuit 60 selects one of the set values X₀ to X₇ depending on a power control signal P cont (binary signal of 3 bits) input to its control input terminals A, B, and C, to output a set value X on its output terminal. The automatic power control circuit 5 is constructed to include amplifiers 51 and 52, and driving transistor 53 and 54, and other elements which operate in conjunction therewith. The automatic power control circuit 5 supplies control outputs Vdd₁ and Vdd₂ having magnitudes depending on the set value X from. the set point providing circuit 6′, to the power amplifier circuit 1. The value of the minimum transmission power P min is adjustable by a minimum value adjusting voltage V min input from the minimum power adjusting variable register 7 to the amplifier 51. The transmission wave signal from the power amplifier circuit 1 is turned off by stopping application of a power voltage V cc to the transistor 54. The stopping of the power voltage V cc is performed in a part of the circuit which is not shown, according to an OFF signal from the microprocessor 24 shown in Fig. 1. Operations of the circuits shown in Fig. 2 are described next. The RF signal input to the power amplifier circuit 1 is amplified to be output as a transmission wave signal. The transmission wave signal is AM detected in the detecting circuit 2, and the power of the transmission wave signal currently output is detected as a detected output V₁. The detected output V₁ is input to the carrier indicator 3′ and to the automatic power control circuit 5. The optimum transmission power of the power amplifier circuit 1 is decided according to the electrical field strength. The power control signal P cont corresponding to the decided transmission power is input to the set point providing circuit 6′. The set point providing circuit 6′ selects a set value corresponding to the power control signal P cont from among the X₀ to X₇ to be output to the automatic power control circuit 5 as a selected set value X. In the automatic power control circuit 5, the amplifier 51 amplifies the result of subtraction of the divided voltage by the variable resistor 7 from the set value X, to output voltage V₂ , the amplifier 52 amplifies the result of subtraction of the detected output V₁ from the output voltage V₂ to drive the transistor 53, and the control outputs Vdd₁ , and Vdd₂ are generated. The power amplifier circuit 1 is controlled by the control outputs Vdd₁ and Vdd₂ so that desired transmission power is output. Adjustment of values of the minimum and maximum transmission power is performed by the variable resistor 7 for adjustment of the minimum power, and the variable resistor 8 for adjustment of the maximum power, respectively. Figure 3 shows the characteristics of the transmission power in the power amplifier 1 corresponding to the set values X₀ to X₇. The value of the minimum transmission power P min corresponding to the set value X₇ can be adjusted with the variable resistor 7 for adjustment of the minimum power, and the value of the maximum transmission power P max corresponding to the set value X₀ can be adjusted with the variable register 8 for adjustment of the maximum power. The carrier indicator 3′ (Fig. 2) is a circuit for generating a signal to indicate whether the transmission wave signal from the power amplifier circuit 1 exists or not. The detected output V₁ from the detecting circuit 2 is compared with the reference value V ref generated in the variable resistor 4 for adjustment of the reference value, and if the detected value V₁ is lower than the reference value V ref , then the transmission wave signal is determined not to exist. The reference value V ref is required to be set lower than a value corresponding to the minimum transmission power P min . Generally, the reference value V ref is set at a value corresponding to a transmission power which is lower than the minimum transmission power P min (for example, lower than 1 mW) by more than 4 dB (Fig. 3). In the aforementioned conventional circuits, the reference value V ref is required to be additionally adjusted with the variable register 4, after the maximum value P max and the minimum value P min of the transmission power have been adjusted with the variable resistor 8 and the variable resistor 7, respectively. Therefore, there are so many portions to be adjusted that production processes are quite numerous. Additionally, the scale of the circuits is large and their cost is high, since a variable resistor for adjustment of the reference value V ref is required. Figure 4 shows a basic construction of the present invention. A transmission amplifier means 11 outputs a transmission wave signal having variable transmission power. A detecting means 12 detects the transmission wave signal from the transmission amplifier means 11. A set point providing means 13 generates set values corresponding to each value of the transmission power. An automatic power control means 14 automatically controls the transmission amplifier means 11 so as to output the transmission power corresponding to the set value of the set point providing means 13, referring to the detected output of the detecting means 12. The transmission interruption detecting means 15 decides existence or absence of the transmission wave signal by comparing the detected output of the detecting means 12 with a reference value generated from a minimum set value in the set point providing means 13. An adequate reference value can be automatically generated, for example, by dividing the minimum set value. Therefore, an adjusting means for generating the reference value is not required, and a working process for adjustment of the reference value is not required. Figure 5 represents an embodiment of the present invention. The same reference numerals as used in Fig. 2 are used for constituents which have the same construction as those in Fig. 2. The circuits shown in Fig. 5 differ from those in Fig. 2 in that the variable resistor 4 for adjustment of the reference value is not used. The reference value V ref is generated by dividing the set value X₇ with serially connected resistors 68 and 69. The values of the resistors 68 and 69 are selected so that the generated reference value coincides with a decision point to decide the transmission interruption as shown in Fig. 3 (for example, a value lower than the set value X₇ by more than 4 dB). In this construction, the reference value V ref for the carrier indicator 3 is automatically set when the maximum and minimum transmission power of the power amplifier circuit 1 is adjusted with the variable resistors 8 and 7. Accordingly, an adjustment process of the reference value V ref is left out and the variable resistor 4 for adjustment is not required. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: A variable transmission power type transmitter comprising: a transmission amplifier means (11;1) for outputting a transmission wave signal having variable transmission power, a detection means (12;2) for detection of a level of the transmission wave signal, an automatic power control means (14;5) for automatic control of the transmission power of said transmitter amplifier means (11;1) depending on the difference between a generated value and a detected output of said detecting means (12;2), a set point providing means (13;6) for generating set values (X₀-X₈) and for selecting one (X) of the set values (X₀-X₈) to be supplied as said generated value to said automatic power control means (14;5), and a transmission interruption detecting means (15;3) for detecting existence or absence of the transmission wave signal by comparing the detected output of said detecting means (12;2) with a reference value generated from one (X₈) of the set values (X₀-X₈) in said set point providing means (13;6); characterised in that means (7,8) are provided for simultaneously adjusting all the set values (X₀-X₈) generated by the set point providing means (13;6) according to selected lower and upper values (P min , P max ) of the transmission power corresponding to the lowest and highest set values generated by the set point providing means (13;6), whereby both said generated value and said reference value are simultaneously adjusted by said level adjusting means (7,8) according to said selected lower and upper values (P min , P max ) of the transmission power. A variable transmission power type transmitter as claimed in claim 1, wherein said set point providing means (13;6) generates said reference value by dividing said one set value for said transmission interruption detecting means (15). A variable transmission power type transmitter as claimed in claim 2, wherein said set point providing means (13;6) comprises a plurality of resistors (61 to 69) for generating a plurality of voltage signals corresponding to said set value, said generated value and said reference value, and a switching circuit (60) for selecting said one set value to be supplied as said generated value to said automatic power control means (14;5), according to an external command.

Inventors: MATSUMOTO YOSHIHIRO, TODA YOSHIFUMI, MATSUMOTO, YOSHIHIRO, TODA, YOSHIFUMI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: H04B7
IPC codes: H04B7