Abstract:
In general, in one aspect, the disclosure describes an amplifier that includes a first transistor coupled to ground and a second transistor coupled to the first transistor and a supply voltage. A voltage biasing circuit is used to provide biased voltages to the first and second transistors. An inductor coupled between the voltage biasing circuit and the second transistor.

Description:
BACKGROUND 
       [0001]    Amplifiers are commonly utilized in circuit designs. Amplifiers may provide limited gain in certain technologies at a frequency band of interest. In order to enhance the gain the amplifier may utilize more current or may incorporate more stages. Such changes to the amplifier may result in additional power being consumed by the amplifier and/or the amplifier requiring additional die area. Additionally, modifying the amplifier may effect (increase) the noise figure of the amplifier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]    The features and advantages of the various embodiments will become apparent from the following detailed description in which: 
           [0003]      FIG. 1A  illustrates a high level schematic diagram of an example tuned cascode amplifier, according to one embodiment; and 
           [0004]      FIG. 1B  illustrates a simplified detailed schematic diagram of an example tuned cascode amplifier, according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0005]      FIG. 1A  illustrates a simplified schematic diagram of an example tuned cascode amplifier  100 . The amplifier  100  includes a first transistor  110  (common source) and a second transistor  120  (common gate) connected in series (drain of  110  to source of  120 ) between ground and a supply voltage (Vdd). The first transistor  110  is illustrated as being directly connected to ground (source to ground) but is not limited thereto. Rather the first transistor  110  is electrically coupled to ground, and other components (not illustrated), such as inductors, may be connected between the first transistor  110  and ground. 
         [0006]    The amplifier  100  also includes an input matching network  130 , an output matching network  140 , a current source  150 , a voltage biasing circuit  160 , a resistor  170 , and an inductor  180 . The input to the amplifier  100  is provided to the gate of the first transistor  110  via the input matching network  130 . The drain of the second transistor  120  provides the output of the amplifier  100 . At least a portion of the output matching network  140  is provided between the second transistor  120  and Vdd. The output matching network  140  may also include other elements not shown that are located elsewhere (e.g., in circuitry receiving the output of the amplifier  100 ). The current source  150  is connected between Vdd and the voltage biasing circuit  160 . The voltage biasing circuit  160  utilizes the current source  150  and Vdd to bias the voltage provided to the first and second transistors  110 ,  120 . The resistor  170  is coupled between the voltage biasing circuit  160  and the gate of the first transistor  110 . The resistor  170  has a large value so that the bias voltage provided thereto has low noise. In some cases resistor  170  may be replaced with an inductor. 
         [0007]    The inductor  180  is coupled between the voltage biasing circuit  160  and the gate of the second transistor  120 . The inductor  180  increases the gate inductance, lowers the input impedance (looking into source), and increases the output impedance of the second transistor  120 . This in turn reduces Miller feedback from gate to drain capacitance (Cgd) of the first transistor  110 . These changes enhance the gain of the amplifier  100  from what it may have been without the inductor  180 . The enhanced gain may be achieved without increasing (or substantially increasing) the noise figure of the amplifier  100 . The improvement in gain without an increase in noise figure results in an increase in the sensitivity of the amplifier  100 . 
         [0008]    The inductor  180  may provide some beneficial tuning of the second transistor  120 . The inclusion of the inductor  180  may also shift the tuning of the amplifier  100 . However, the shift in tuning of the amplifier  100  may be easily accommodated by re-tuning the input and output matching networks  130 ,  140 . 
         [0009]    The amount of gain that is desired and achieved depends on the application and technology employed to implement the amplifier  100 . A desired gain increase may be on the order of 3-6 db. A larger increase in gain may cause instability. The desired gain may be achieved with a relatively modest value (e.g., 100-500 pico-Henries) for the inductor  180 . The inductor value is large enough to control, but small enough not to require significant die area. 
         [0010]    The voltage biasing circuit  160  may be located apart from the second transistor  120  so that the inductor  180  can be formed in interconnect metal so that no additional die area is required to implement. 
         [0011]    The use of the inductor  180  can be implemented to enhance the gain of a high-frequency amplifier. A high-frequency low noise amplifier may be one practical application of the use of the inductor  180 . The use of the inductor  180  may increase the gain in amplifiers and systems with marginal capability/performance for a given power consumption. In a scaled digital CMOS process where the transistors have severe short channel effects (low output resistance) and/or low Q inductors (or with resistive loads), this technique can be employed to increase gain which would otherwise be low. The increased gain is important for making high-performance radios, such as those fabricated in CMOS, particularly scaled CMOS, and digital CMOS. 
         [0012]    Gain boosting generated by the inductor  180  may also be used to obtain adequate performance at lower current to save power for battery operated devices. This may enable low power operation of a receiver in a radio by reducing the noise contribution of later components in the receiver chain. A low power receiver is important for a variety of radio standards, particular if they operate from a battery. 
         [0013]      FIG. 1B  illustrates a simplified detailed schematic of the example amplifier  100 . The input matching network  130  may include a series inductor  132  coupled to the gate of the first transistor  110 . The inductor  132  may be coupled in series to a capacitor  134 . The input matching network  130  may include other components that are not illustrated for ease of understanding. The input matching network  130  is in no way intended to be limited to the inductor  132  and capacitor  134  in series. Rather, the input matching network  130  can be any type of RF circuitry (e.g., spiral inductors) utilized for matching of the input that does not interfere with the voltage bias being applied to the gate of the first transistor  110 . 
         [0014]    The output matching network  140  may include an inductor  142 . It may also include other components that are not illustrated for ease of understanding. The output matching network  140  is in no way intended to be limited to the inductor  142 . Rather, the output matching network  140  can be any type of RF circuitry utilized for matching of the output. 
         [0015]    The voltage biasing circuit  160  may include two transistors  162 ,  164  connected in series. The gates of each of the transistors  162 ,  164  may be connected to the drain of the transistors  162 ,  164  to provide a DC voltage for biasing. The voltage biasing circuit  160  is in no way intended to be limited to transistors  162 ,  164 . Rather, the voltage biasing circuit  160  can be a battery, capacitor or any type of analog and/or RF circuitry that provides biasing and a low impedance to the gates of the transistors  110 ,  120 . 
         [0016]      FIGS. 1A and 1B  illustrated the tuned cascode amplifier  100  as two transistors  110 ,  120  in series, however the amplifier  100  is in no way intended to be limited thereto. Rather, various other embodiments are within the current scope. For example, the common gate transistor  120  could be two transistors in series. The bias provided to the gate of the two transistors could be the same, could be different but be supplied from the same voltage biasing circuit  160 , or the bias provided to one of the transistors could be provided from an alternative bias source (not illustrated). The amplifier  100  may include auxiliary circuitry (e.g., one or more transistors) for improved linearity where the auxiliary circuitry is on an auxiliary path (e.g., in parallel to the transistors  110 ,  120 ). Neither, the auxiliary circuitry nor the auxiliary path are illustrated. 
         [0017]    Although the disclosure has been illustrated by reference to specific embodiments, it will be apparent that the disclosure is not limited thereto as various changes and modifications may be made thereto without departing from the scope. Reference to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described therein is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” appearing in various places throughout the specification are not necessarily all referring to the same embodiment. 
         [0018]    The various embodiments are intended to be protected broadly within the spirit and scope of the appended claims.