Abstract:
The subject matter discloses a method of amplifying a signal, the method comprising receiving a command to start transmission, gradually increasing a value of an enable signal used to amplify the transmission and intermittently transmitting the value of the enable signal to an enable transistor used to allow amplifying a transmitted signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to amplifying a signal in general and to amplifying a signal using ramping in particular. 
     2. Discussion of the Related Art 
     High quality radio frequency (RF) signals must ramp quickly from a condition of minimal output power to a condition of information-bearing modulation at a specified output power and back down to the condition of minimal output power. Such power ramping capability is required for transmitters in many Time Division Multiple Access (TDMA) communication systems and other transmitters. Examples to such TDMA systems include those specified by the DECT, GSM and ansi-136 standards, and combinations of the same. 
     A fundamental requirement of these transmitters is that the acts of ramping up and ramping down must not violate specified limits on peak power in spectral bands away from the assigned RF channel. Such bands would be allocated to other transmitters. The associated measurement is called the transient spectrum in some systems or the transient adjacent channel power (transient ACP) in others. 
     In many cases, E class amplifiers comprise two transistors connected serially, to form a widely used cascode cell. In many cases, amplifier input signal is such the AC amplitude is higher than the DC amplitude, which makes difficult to disable the transmission. To achieve the disabling, the voltage value of the DC should be negative, which requires additional hardware modules, such as negative voltage generator. 
       FIG. 1A  shows a graph of voltage provided to the amplifying unit, in accordance with an exemplary embodiment of a prior art transmitter. The normal operation DC voltage  110  is 0.5 to 0.7 volts, and the AC voltage  120  has amplitude of 1 volt or higher. The standard threshold voltage of the amplifier is about 0.5 to 0.7 v, which means that the DC voltage is required, to disable the amplification, has to be negative, such as negative DC voltage  130 . 
     It is desired to provide a transmitter having an amplifying unit that avoids the requirement for negative power. 
     SUMMARY OF THE PRESENT INVENTION 
     The subject matter discloses a method of amplifying a signal, the method comprising receiving a command to start transmission and gradually increasing a value of an enable signal used to amplify the transmission. The method also comprises intermittently transmitting the value of the enable signal to an enable transistor used to allow amplifying a transmitted signal. 
     In some cases, the method further comprises a step of generating a trapezoid signal used to gradually increase the value of the enable signal. 
     In some cases, the method further comprises a step of converting a square signal into the trapezoid signal. In some cases, the trapezoid signal is received at the enable transistor. In some cases, the transmitted value is an impedance value. 
     It is another object of the subject matter to disclose a transmission unit, comprises an amplifying module. The amplifying module comprising: a common source transistor and an enable transistor used to allow transmission of signals from the transmission unit. The enable transistor receives a gradually increased signal in an intermittent manner. 
     In some cases, the transmission unit further comprising a mechanism for generating a trapezoid signal used to gradually increase the signal; 
     In some cases, the transmission unit further comprising a mechanism for converting a square signal into the trapezoid signal. 
     In some cases, the mechanism comprises a reverse counter for detecting signals received from a control unit and an accumulator for summing the number of detected signals. In some cases, the detected signals are selected from a group consisting of enable and disable signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary non-limited embodiments of the disclosed subject matter will be described, with reference to the following description of the embodiments, in conjunction with the figures. The figures are generally not shown to scale and any sizes are only meant to be exemplary and not necessarily limiting. Corresponding or like elements are optionally designated by the same numerals or letters. 
         FIG. 1A  shows a graph of voltage provided to the amplifying unit, in accordance with an exemplary embodiment of a prior art transmitter; 
         FIG. 1B  shows a transmitter using a ramping technique, according to exemplary embodiments of the subject matter; 
         FIG. 2  shows an amplifying module using a ramping technique, according to exemplary embodiments of the subject matter; 
         FIG. 3  shows a transmitter utilizing a gradually adjusted impedance, according to exemplary embodiments of the subject matter; 
         FIG. 4  shows a mechanism for generating a gradually adjusted impedance, according to exemplary embodiments of the subject matter; 
         FIG. 5  shows a graph of a gradually amplified signal, according to exemplary embodiments of the subject matter; and, 
         FIG. 6  shows a method of gradually amplifying a signal, according to exemplary embodiments of the subject matter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     One technical challenge disclosed in the subject matter is to provide disabling of an amplifying unit without the need to send a negative voltage signal to the amplifying unit. Another technical problem is to reduce the amount of bandwidth required when the transmitted signal increased too rapidly. 
     One technical solution of the disclosed subject matter is to provide gradual amplification to a transmitter using ramping technology. This may be achieved by providing a trapezoid signal from an enable module of a transmitter, used to enable transmission, to an amplifying unit. 
       FIG. 1B  shows a transmitter using a ramping technique, according to exemplary embodiments of the subject matter. The transmitter  140  comprises one or more amplifying modules, such as  150 ,  152  and  154 . The one or more amplifying modules may be connected in parallel. In some exemplary cases, each of the one or more amplifying modules comprises three transistors. For example, amplifying module  150  comprises a common source transistor  160 , a common gate transistor  168  and an enabling transistor  164 . 
     The common source transistor  160  functions as a voltage amplifier, in which input voltage modulates the amount of current flowing through the transistor and changes the voltage across the output resistance according to Ohm&#39;s law. The combination of both the common source transistor  160  and the common gate transistor  168  forms a cascode cell. The cascode cell has several well known advantages and is widely used. The common gate transistor  168  is optional in the amplifying module  150  and is not an integral module within said amplifying module  150 . 
     While prior art enabling transistors provide a binary control for enabling the signal in the amplifier, which results in immediate start of transmission. The enabling transistor of the disclosed subject matter provides a gradually increased signal that provides a precise control on the pace of increased and decreased power outputted from an amplifying module, such as  150 . The gradually increased voltage may be provided in multiple techniques, as detailed below. 
       FIG. 2  shows an amplifying module using a ramping technique, according to exemplary embodiments of the subject matter. The amplifying module  200  comprises a common gate transistor  210  and a common source transistor  220  operating to amplify a signal to be transmitted. The amplifying module  200  further comprises an enable transistor  230 , changing its impedance according to a signal. The impedance provided from the enable transistor  230  to the common source transistor  220  is provided in a non-binary manner, for example a trapezoid signal comprising intermediate values other than zero and the maximal level. The common source transistor  220  may receive an AC signal via a capacitor and a DC bias signal via a resistor. 
     The trapezoid impedance presented by the enable transistor  230  provides for gradual conductivity of the common source transistor  220  as a function of the voltage provided to the enable transistor  230 . For example, over a period of 0.1 seconds, the impedance provided from the enable transistor  230  to the common source transistor  220  gradually increased from 0Ω to 2.5Ω. Such gradual increase may be in intermediate values of 0.05Ω, for example providing 0.05Ω, 0.1Ω, 0.15Ω and the like. Providing the common source transistor  220  with intermediate levels of impedance results in gradual increase in the amplified signal outputted from the transmitter. For example, when providing impedance level of substantially zero, the enable transistor enable amplifying the signal, as no resistance is provided. As the resistance is increased, for example 100 kΩ, amplifying the signal using the common source transistor  220  is disabled as the voltage on the enable transistor is approximately zero. Further, gradual indication as to whether transmission should begin, as provided by the gradual impedance from the enable transistor  230  requires less bandwidth than required when sending a YES/NO indication as provided in prior art transmitters. 
     In some exemplary embodiments of the disclosed subject matter, the enable transistor  230  receives a command from a control unit, such as  170  of  FIG. 1B . The control unit may send a pulse used to gradually increase the impedance outputted from the enable transistor  230 . Alternatively, the data from the control unit may be received at a ramping unit such as  234 , used to convert the data from the control unit as a trapezoid voltage or gradually increased voltage to the enable transistor  230 . Alternatively, the ramping unit may reside within the enable transistor  230 . In such case, the enable transistor  230  receives a square signal such as signal  232  and outputs trapezoid impedance such as signal  236 . 
     In some cases, a transmitter may comprise several common source transistors; each common source transistor is connected to a specific enable transistor. Several common source transistors, such as  220 , may be connected to one common gate transistors in parallel. 
       FIG. 3  shows a transmitter utilizing a gradually adjusted impedance, according to exemplary embodiments of the subject matter. The transmitter provides a configuration, according to which a specific enable transistor is not related to a specific amplifying unit as described in  FIG. 1B . Transmitter  300  comprises multiple enable transistors, such as  310 ,  312  and  314 . Each of the enable transistors receives a signal from a control unit. In some embodiments, each enable transistor receives a signal from a different control unit. Alternatively, several enable transistors receive a signal from the same control unit. The signal from the control unit may be 0 or 1, or another square wave implementation. The signal may be converted to a trapezoid impedance by a ramping unit connecting the control unit  322  and the enable transistor  312 . 
     The transmitter  300  further comprises one or more common source transistors, such as  340 ,  342  and  344 . In some exemplary cases, each common source transistor is connected to a specific enable transistor and receives an enable indication from the specific enable transistor, an indication that controls the amplifying of data transmitted from the transmitter  300 . A sequence of common source transistor and an enable transistor are connected in series. Each pair of a common source transistor and an enable transistor is connected in parallel to another pair. While prior art transmitters used a square wave indication from the enable transistor to the transistor controlling the amplifying, the subject matter provides for an indication impedance having two or more levels of signals. Such impedance may be resistance values, such as 10 ohms, 20 ohms, 30 ohms such that the impedance is increased gradually during a period of time in which a sequence of impedance values are provided from the enable transistor to the common source transistor. Such sequence of impedance values may be the gradual indication of amplifying the transmission, or an indication concerning start of transmission. The transmitter  300  may also comprise one or more common gate transistors  352 , connected in series to the parallel array of pairs of common source transistor and an enable transistor. For example, a first pair comprises enable transistor  310  and common source transistor  340  and a second pair comprises enable transistor  312  and common source transistor  342 . Common gate transistor  352  is connected in series to the parallel connection of first pair and the second pair. 
       FIG. 4  shows a mechanism for generating a gradually amplified voltage, according to exemplary embodiments of the subject matter. The mechanism receives a square wave signal and generates a trapezoid voltage used to gradually amplify transmission from the transmitter, such as transmitter  300 . The mechanism  400  receives a signal from a control unit that controls one or more amplifying units via enable transistors. The mechanism may reside between the control unit and the enable transistor, receive signals from the control unit and send gradually increased voltage values to one or more enable transistors. Alternatively, the mechanism  400  may reside in the control unit or in the enable transistors themselves. 
     The mechanism  400  may include a receiving unit  450 , a reversible counter  410 , and a transmission unit  430 . The mechanism may also comprise a clock  440 . The receiving unit  450  receives a signal from the control unit. The signal is a square wave, and may have a value of “1” or “0”, or another implementation of “enable” signal or “disable” signal. The reversible counter  410  sums the amount of times an “enable” signal was received at the receiving unit  450  from a control unit. The reversible counter  410  subtracts the number of “disable” signals from the number of “enable” signals. The reversible counter  410  may also subtract a unit from the voltage value provided to the enable transistor in case there is no “enable” signal received from the control unit for a predefined period of time, for example 75 ms. The clock  440  is used to provide indication for the embodiment disclosed above. Transmission unit  430  is used to provide the voltage value determined by the reversible counter  410  to the enable transistor. The trapezoid signal may be a sequence of voltage values determined by the reversible counter  410  or by a processing unit in the mechanism  400 . The sequence of values comprises three or more values, such that there are intermediate voltage values received at the enable transistor other than “enable” and “disable”. The transmitter may also include a Digital to Analog converter  420  for converting values received from the control unit, or values from a clock unit, into voltage values to be passed to the amplifying unit. 
     The gradual increase performed by the mechanism  400  provides that the amplification of the signals outputted from the transmitter  300  is gradual. This results in less bandwidth required in the transmitter, and prevents the requirement to use negative voltage. Another result is reducing the load on the electrical appliances in the transmitter. 
       FIG. 5  shows a graph of a gradually amplified voltage, according to exemplary embodiments of the subject matter. The graph shows a gradual increase and gradual decrease in the voltage passed to the enable transistor. The value is increased upon indication from a control unit, for example upon receipt of an “enable” signal from the control unit. When receiving an “enable” signal, or in case of receiving an “enable” signal for a predefined duration, such as 10 ms, the value is increased by 1 or by another predefined number. The value may be decreased in a gradual manner upon receipt of a “disable” signal, or upon lack or receipt of an “enable” signal. The value transmitted to the enable transistor within the trapezoid signal may be limited to a predefined value, according to the specification of the transmitter or any module within the transmitter. 
       FIG. 6  shows a method of gradually amplifying a signal, according to exemplary embodiments of the subject matter. In step  610 , a signal is received from a control unit. The received signal has a characteristic of a square wave, for example having only two values, “enable” and “disable”. In step  620 , the signal received from the control unit is converted into a trapezoid signal. The trapezoid signal comprises a sequence of values transmitted to the enable transistor. For example, a sequence of values may be [0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.4, 0.5, 0.6, 0.7, 0.7, 0.5, 0.3, 0]. In step  630 , the trapezoid signal is generated, for example by a ramping unit, or by a unit residing within the enable transistor. In such case, the trapezoid signal is transmitted from the enable transistor to the common gate transistor or to another module in the amplifier. In step  640 , the trapezoid signal is transmitted from the unit that generated the signal. The trapezoid signal may be transmitted from a ramping unit to the enable transistor, or from the enable transistor to the amplifier. In step  650 , amplification is performed gradually because the signal is received at the amplifier in gradually increased values. In some exemplary cases, when the impedance value provided from the enable transistor is substantially zero, voltage in the amplifying unit and the common gate transistor is enabled and transmission is enabled. When the impedance is increased, transmission is disabled. 
     While the disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings without departing from the essential scope thereof. Therefore, it is intended that the disclosed subject matter not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but only by the claims that follow.