Configurable power amplifier and bias control

Details Configurable power amplifier and bias control Configurable power amplifier and bias control

2001-10-05

2003-09-09

Young, Brian (Department: 2819)

Amplifiers

With semiconductor amplifying device

Including current mirror amplifier

C330S285000, C330S296000

Reexamination Certificate

active

06617928

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to maximizing the efficiency of radio frequency power amplification in a wireless communication device transmitter, and, more particularly, to a high efficiency multiple power level amplifier.
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 amount of power consumed and dissipated becomes more and more critical. High efficiency power amplification decreases the amount of power consumed, thereby maximizing battery life of the device.
Another major concern in these wireless devices is the size of the circuitry. In order to minimize the hardware required it is desirable to integrate as much functionality as possible into fewer and fewer circuit modules. This enables the handheld device to be smaller and consume less power.
Many wireless power amplifier applications require high efficiency over a broad range of operating power levels. This is inherently difficult to achieve without circuitry and logic in addition to the power amplifier. Typically, additional circuitry residing on a control die must be used in addition to the power amplifier circuit.
FIG. 1
is a simplified block of a typical transceiver
50
. Transceiver
50
includes a bias circuit
100
, a power amplifier
120
and a voltage regulator
140
. Bias circuit
100
maintains a constant current I
B
to power amplifier
120
based upon a reference voltage V
ref
provided to the bias circuit
100
by the voltage regulator
140
.
Bias control systems to control the level of voltage bias applied to a power amplifier, and thus the level of power consumed by the power amplifier during operation, are often used in conjunction with wireless communications devices incorporating power amplifiers. One example of such a bias control system is illustrated in FIG.
2
. In this example, an emitter follower bias circuit
100
is illustrated. The emitter follower bias circuit
100
provides a base current I
B
required by a radio frequency (RF) power amplifier
120
, and more particularly, RF transistor
32
for direct current (DC) bias and RF power conditions. Both emitter follower bias circuit
100
and power amplifier
120
are typically implemented using the same semiconductor technology, for example, gallium arsenide (GaAs) heterojunction bipolar transistor (HBT).
One of the primary disadvantages of this type of common bias control system when implemented using GaAs HBT technology is that due to the two base emitter voltage drops across buffer transistor
30
and RF transistor
32
, respectively, V
ref
must be greater than +3.0V to maintain adequate operation over the operating temperature range as the base to emitter voltage drop V
BE
of each of these transistors is approximately +1.3 volts each. However, in many communications devices, such as mobile cellular or PCS telephones, batteries are used to provide a supply voltage to the communications device. These batteries are typically configured to provide a minimum operating voltage of +2.8 VDC. Communications devices are often configured to shut off when the available supply voltage falls below +2.8 volts DC (VDC). Once the available battery voltage drops below +3.0 VDC, it is necessary for steps to be taken to boost the sub +3.0 VDC operating voltage supplied by the battery up so that the voltage supplied to the communications device as VDC is the required +3.0 volts. This requires additional circuitry to boost the sub +3.0 VDC voltage and provide a regulated voltage to the communications device that is greater than the minimum battery voltage.
Further, as an external voltage is typically required to provide a reference voltage V
REF
to the bias circuit
100
, an external input
49
is provided to connect an external voltage supply to the bias circuit
100
. In RF communications devices, electrostatic discharge (ESD) can damage the circuitry of the communications device. ESD may be propagated through the circuitry of the communications device via connections between circuitry/components. The presence of an external input
49
reduces the reliability of the bias circuit
100
, as well as the communications device
150
in general, as it increases the risk of ESD being picked up and propagated through the bias circuit
100
, thereby potentially damaging the bias circuit
100
and/or power amp
120
. GaAs HBT technology typically provides resistance to ESD of up to ±1 kilovolt (1 KV). ESD exceeding ±1 KV is common and jeopardizes circuitry of the communications device.
Additionally, in the communications device
150
, the base current (I
B
)
RF
provided to the RF transistor
32
of power amplifier
120
is prone to shift as the power required by RF transistor
32
increases/decreases. Thus, in order to compensate for such shifting in bias current, it is common to provide a higher bias voltage to the base of the RF transistor
32
. This leads to lower efficiency, greater consumption of power and the need for a higher supply voltage.
The bias circuit
100
is typically configured to provide a quiescent current (I
B
) to the RF transistor
32
that allows for maximum gain and linearity at the maximum RF output power level. However, at low power levels this fixed quiescent current is higher than necessary for proper operation at the lower power levels. As a result the efficiency of the power amp
120
diminishes at lower RF output levels.
The voltage at node
34
is established by the base-to-emitter drop of the mirror transistor
26
and the buffer transistor
30
. The voltage at node
34
establishes the reference current I
ref
which flows through the resistor R
ref
. As the base to emitter voltage drop of a transistor fluctuates as temperature fluctuates any changes in temperature impact the voltage at node
34
. Thus, as the temperature changes and the base to emitter voltages across mirror transistor
26
and buffer transistor
30
change, the voltage at node
34
changes. This results in the current I
ref
also changing. As I
ref
varies so will the output current I
C
at RF transistor
32
. Unfortunately, as the current I
C
decreases so does the linearity of RD transistor
32
.
Therefore, there is a need in the industry for a wireless power amplification circuit that achieves highly efficient power amplification over a broad range of output power levels and that is economical to produce in high volume.
SUMMARY
The present invention provides a system for biasing a power amplifier in a communications device. Briefly described, in architecture, the system can be implemented as follows. A band gap voltage generator for generating a bandgap voltage is provided to a voltage-to-current converter. The voltage-to-current converter generates a reference current in accordance with the bandgap voltage. The reference current is provided to a programmable current mirror that multiplies the reference current to a predetermined level. A feedback amplifier is provided for outputting and maintaining a constant current to a reference device.
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

Affiliated with

Also associated with

Rating

Configurable power amplifier and bias control does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Configurable power amplifier and bias control, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Configurable power amplifier and bias control will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3018050