Power amplifier circuit for providing constant bias current...

Details Power amplifier circuit for providing constant bias current... Power amplifier circuit for providing constant bias current...

2000-11-27

2002-07-23

Lee, Benny (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including temperature compensation means

C330S296000, C327S513000, C323S312000

Reexamination Certificate

active

06424225

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to improving the efficiency of radio frequency power amplification in a wireless communication device transmitter, and more particularly, to a power amplifier circuit for providing constant bias current over a wide temperature range.
2. Related Art
With the increasing availability of efficient, low cost electronic modules, mobile communication systems are becoming more and more widespread. For example, there are many variations of communication schemes in which various frequencies, transmission schemes, modulation techniques and communication protocols are used to provide two way voice and data communications in a handheld telephone-like communication handset. While the different modulation and transmission schemes each have advantages and disadvantages, one common factor is the need for highly efficient power amplification. As these communication devices become smaller and smaller, the functionality provided by these devices continues to increase. One major concern when developing these handheld communication devices is power consumption. As the devices become smaller and smaller, the need to manage the amount of power consumed and dissipated becomes more and more critical. High efficiency power amplification decreases the amount of power consumed, thus maximizing the life of the power source of the device.
Most wireless power amplifier applications require high efficiency, gain and linearity over a broad range of operating temperatures. Because these features are typically difficult to achieve in the power amplification circuitry, additional circuitry and logic are required to achieve these goals.
Bias circuitry, that is typically present in power amplification circuits, is used to provide a “reference current” to the radio frequency (RF) power amplification device. A reference device, that can be for example but not limited to, a reference amplifier implemented using one or more transistors, provides the reference current. Th reference current is multiplied to generate a proper bias current for the RF amplification device. Unfortunately, the reference current fluctuates with temperature, resulting in undesirable performance variations in the RF power amplification device due to variations in the reference current caused by the temperature fluctuations.
FIG. 1
is a schematic view illustrating a conventional bias circuit for a radio frequency (RF) power amplifier. Power amplifier circuit
100
includes reference transistor
106
(designated “Q
REF
”) through which a reference current flows. The reference current flows from the voltage source V
REF
through resistor
102
into the collector terminal
104
of reference transistor
106
. The reference current then flows through the emitter terminal
108
to ground. The reference current also flows through connection
112
and through connection
110
to buffer circuitry
114
. Connection
112
connects the base terminal
110
of the reference transistor
106
to the collector terminal
104
of reference transistor
106
. The reference current then flows through buffer circuitry
114
to the base terminal
116
of power transistor
122
. This reference current, sometimes referred to as the bias current, present at the base terminal
116
of power transistor
122
regulates the flow of current from the node V
CC
(RF OUT)through power transistor
122
.
In operation, an RF input signal is applied to node
118
labeled “RF IN” through capacitor
120
to the base terminal
116
of power transistor
122
. The RF signal is then amplified by power transistor
122
as a function of the current flowing through the power transistor
122
. The buffer circuitry
114
, the detail of which has been omitted for simplicity, includes additional circuitry that allows the low beta transistors
106
and
122
, each of which have high base currents, to support those high base currents. In this manner, the buffer circuitry
114
supplies the base current required by the power transistor
122
. In addition, the buffer circuitry
114
includes circuitry that prevents the RF signal applied to node
118
from coupling back into the bias circuitry
130
, and in particular, from adversely affecting the reference transistor
106
. The output of the power transistor
122
is taken from the collector
124
at the node labeled “RF OUT.” The current flowing in the collector
124
is defined as I
R
N=*I
REF
, where N is a multiplication factor, or ratio, between reference transistor
106
and the power transistor
122
.
The reference current flowing through the bias circuitry
130
may vary with temperature, resulting in an undesirable performance variation over temperature. For example, the bias current (reference current) includes temperature dependencies that follow the following equations:
I
cq
∝T
&dgr;/2
  Equation 1
I
cq
∝T
  Equation 2
where I is the reference current, cq is the quiescent current at the collector of the reference transistor, ∝ indicates proportionality, and T is the temperature.
Therefore, there is a need in the industry for a temperature independent wireless power amplification bias circuit that allows the power amplifier to achieve highly efficient power amplification over a broad range of temperature variations and that is economical to produce in high volume.
SUMMARY
The invention provides a temperature stable bias circuit for an RF power amplifier. The bias circuitry uses current deletion and current supplement techniques to maintain the bias or reference current of the RF power amplifier at a stable level regardless of the temperature under which the power amplifier is operating. When temperature increases, the current deletion circuitry reduces the bias current supplied to the power transistor. When the temperature decreases, the current supplement circuitry increases the bias current supplied to the power transistor. The bias circuitry allows the output of the RF power amplifier to remain constant. The current deletion and current supplement circuitry can be fabricated using the same processing technology as the power amplifier and can be easily integrated into the power amplifier device packaging.
Related methods of operation and computer readable media are also provided. Other systems, methods, features, and advantages of the invention will be or become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.


REFERENCES:
patent: 4727269 (1988-02-01), Luich
patent: 6052032 (2000-04-01), Jarvinen
patent: 6297685 (2001-10-01), Ewen et al.
patent: 6297709 (2001-10-01), Wey et al.

Affiliated with

Also associated with

Rating

Power amplifier circuit for providing constant bias current... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Power amplifier circuit for providing constant bias current..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power amplifier circuit for providing constant bias current... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2902506