Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
1999-08-06
2001-08-07
Lee, Benny (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S285000, C333S08100R, C333S08100R
Reexamination Certificate
active
06271727
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to power amplifier control and, more particularly, to a high isolation radio frequency (RF) power amplifier having a PIN diode attenuator control circuit for substantially eliminating self-biasing of bipolar devices associated with the RF power amplifier under large signal drive conditions.
(2) Description of the Prior Art
Consumer demand for wireless communication is ever increasing worldwide, placing a burden on the existing cellular infrastructure. In Europe, the increased demand led regulators to create the DCS cellular telephone band. DCS utilizes GSM baseband technology at canier frequencies near 1.8 GHZ.
Also in response to consumer demand, cellular telephone manufacturers strive to reduce the size and weight of their phones. With the introduction of DCS, and the creation of dual band GSM/DCS phones, the quest for ever smaller components has intensified. Manufacturers frequently specify the use of a 3-volt battery, either a single lithium ion cell, or a plurality of nickel/metal hydride (NiMH) cells to help reduce phone size and weight. With such a power source, manufacturers also specify various specifications for certain performance characteristics. Some of the most important characteristics are associated with low voltage operation, power, high efficiency, small size and power control. For example, many manufacturers presently specify that the DCS power amplifier must be capable of operating with the battery voltage as low as 2.7 volts, with a nominal voltage near 3.2 volts. This specification allows greater utilization of the battery charge to maximize talk time while complying with DCS standards. In view of the foregoing manufacturing specifications, it is desirable in the industry to provide a workable DCS power amplifier utilizing bipolar device technology.
Isolation of bipolar device power amplifiers under large signal drive conditions however, has been particularly problematic. For example, when the control voltage to a power amplifier is at 0 volts, the amplifier should be turned off. During this off condition, the power amplifier generally is required to have a specified minimum isolation between its input and its output. Self-biasing of specific bipolar devices can occur under certain large signal drive conditions. This self-biasing can reduce the aforesaid isolation by turning on one or more stages of a bipolar device implemented power amplifier. Techniques have been developed that attempt to reduce or eliminate the degree of self-biasing described above. Using power amplifiers constructed with MESFET technology help to minimize this problem since they are less susceptible to self-biasing as compared with power amplifiers constructed with bipolar devices. Another technique used to reduce or eliminate the aforesaid self-biasing includes the use of discrete devices to enhance the degree of isolation per stage. Other techniques have also been utilized, including use of a RF switch at the input to the power amplifier.
Although the foregoing techniques may have proven successful in certain limited applications, these techniques are not as desirable in applications specific to integrated circuit design where size and cost constraints are of paramount importance. For example, discrete designs simply are not feasible when a system application necessitates sole use of integrated circuit structures. Additionally, certain technologies, e.g., GaAs HBT technology requires fewer external components than a MESFET design and generally has higher efficiency as well. Further, MESFET's tend to require external switches to be turned off completely under certain operating conditions. Use of such external switches is undesirable when associated with integrated circuit structures since they can add to component count, size and cost.
Thus, there remains a need for a new and improved integrated circuit power amplifier control circuit suitable for use with bipolar device power amplifiers and that effectively minimizes power amplifier self-biasing under large signal drive conditions thereby ensuring optimum isolation between the power amplifier input point and the power amplifier output point, regardless of the amplifier large signal drive level.
SUMMARY OF THE INVENTION
The present invention is directed in part to a PIN diode attenuator system particularly useful in association with an integrated circuit design to effectively minimize self-biasing that can occur under large signal drive conditions associated with bipolar device RF power amplifiers. The PIN diode attenuator is electrically coupled to the RF input of the bipolar device RF power amplifier. One embodiment comprises a RF power amplifier having an RF signal input; a PIN diode electrically coupled to the RF signal input; and a variable current source having a control signal input and configured to adjust current flow through the PIN diode in response to a control signal to the control signal input, such that RF signals to the RF signal input are not attenuated when the RF power amplifier is in its forward gain mode and such that RF signals to the RF signal input are substantially fully attenuated when the RF power amplifier is in its filly off mode and further such that RF signals to the RF signal input are variably attenuated when the RF power amplifier is in a transition state between the forward gain mode and the fully off mode, wherein RF signals to the RF signal input are attenuated to minimize self-biasing associated with the RF power amplifier configured to receive the attenuated RF signals.
Another embodiment uses a HBT RF power amplifier having a RF signal input, a PIN diode having its anode electrically coupled to the RF signal input and its cathode electrically coupled to ground and further having a variable current source including a power amplifier control voltage input and a DC current output, the DC current output being electrically coupled to the anode.
Yet another embodiment uses a RF power amplifier having a RF signal input and a RF signal output; diverting means for diverting a desired portion of a RF signal to ground and away from the RF signal input; and controlling means for varying the desired RF signal portion diverted to ground in response to a power amplifier control signal to generate an attenuated RF signal such that a predetermined isolation is achieved between the RF signal input and the RF signal output.
Still another embodiment comprises a RF amplifier having a RF signal input; a RF signal path associated with the RF signal input, the RF signal path having a predetermined attenuation characteristic; current generating means for providing a variable DC current having a value determined by a RF power amplifier control voltage; and means responsive to the current generating means for changing the attenuation characteristics associated with the RF signal path in response to the variable DC current wherein the attenuation characteristics are dependent upon the value of the DC current necessary to substantially eliminate self-biasing of the RF amplifier when the RF amplifier is not in a forward gain operating mode.
An associated network turns off the RF power amplifier when the power control voltage is at 0 volts, and also turns off all bias to the PIN diode attenuator when the PIN diode attenuator enable input is low, e.g. less than 0.3 volts, such that a switched regulated voltage is not required to make the RF power amplifier operational.
The current through the PIN diode is controlled by two signals: AT_EN and APC. The AT_EN signal allows current flow through the PIN diode and is an on/off function. The APC signal controls the amount of current through the PIN diode. Generally, the AT_EN signal will be derived from the VCO ENABLE signal available in most Global System for Mobile Communications (GSM) handset designs. If maximum isolation is needed before the ramp-up, the AT_EN signal generally needs to be turned on before the RF power is applied to the device input.
The current through the PIN d
Lee Benny
Nguyen Patricia T.
RF Micro Devices, Inc.
Withrow & Terranova, P.L.L.C.
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