Patent Application
20080297262
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.
The features and advantages of the various embodiments will become apparent from the following detailed description in which:
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The various embodiments are intended to be protected broadly within the spirit and scope of the appended claims.
