Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
1999-11-24
2001-10-02
Pascal, Robert (Department: 2817)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S295000, C330S298000, C330S134000
Reexamination Certificate
active
06297694
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high frequency power amplifier for dual band systems used, for example, in mobile telephones, and relates more particularly to a high frequency power amplifier of heterojunction bipolar transistors (HBT) having a bias switching circuit for switching a bias circuit to select a power amplifier.
2. Description of the Prior Art
Monolithic microwave integrated circuits (MMICs) and modules (hybrid ICs and multichip modules) using GaAs metal-semiconductor field effect transistors (MESFETs), GaAs high electron mobility transistors (HEMTs), or GaAs-based HBTs are widely used in power amplifiers for mobile communications devices. Compared with a conventional FET, a GaAs-based HBT does not require a negative gate bias voltage, enabling a single power supply operation, and can effect an on/off operation similarly to a Si-MOSFET but without an analog switch on the drain side. A further advantage is that GaAs-based HBTs can be used to achieve a smaller power amplifier generating a rated output power with a higher output power density than is possible with a conventional FET power amplifier. GaAs-based HBTs are therefore considered promising as power elements in future mobile communication devices.
With recent sharp increases in demand for mobile phones, telephones and services enabling access to two systems using a single handset have been introduced. In Europe, for example, there are two mobile telephone services: GSM 900 (Global System for Mobile Communications), a 900 MHz system that is the most widely used mobile telephone service in Europe, and DCS 1800, a competing system that operates in the 1800 MHz band. Japan also has two systems: Personal Digital Cellular (PDC), a 900 MHz mobile telephone system, and PHS (Personal Handyphone System), a 1900 MHz digital cordless telephone system. So-called dual band mobile phones that can switch between two different telephone services are already available.
FIG. 10
is an exemplary circuit block diagram of a high frequency power amplifier for use in a conventional dual band mobile phone.
Referring to
FIG. 10
, GSM 900 transistors TrA
1
to TrA
3
, that is, HBTs for amplification in the 900 MHz band, are biased by a first biasing circuit
201
. GSM 1800 TrB
1
to TrB
3
, that is, HBTs for amplification in the 1800 MHz band, are biased by a second biasing circuit
202
.
Bias switching circuit
203
exclusively selects and operates either the first biasing circuit
201
or second biasing circuit
202
based on the signal level of a two-valued input signal Vmod applied to the Vmod terminal. The bias switching circuit
203
also passes an output control signal based on the signal level of the input signal Vpc applied to the Vpc terminal to the first biasing circuit
201
or second biasing circuit
202
to adjust the level of the output signal passed from output terminals OUT
1
and OUT
2
. When input signal Vpc is 0 V, the bias switching circuit
203
stops the operation of both the GSM 900 power amplifier and the GSM 1800 power amplifier regardless of input signal Vmod.
FIG. 11
is a typical circuit diagram of the bias switching circuit
203
used in the conventional high frequency power amplifier shown in FIG.
10
. As shown in
FIG. 11
, this bias switching circuit
203
comprises a logic circuit
210
of CMOS or other silicon circuit elements, and an output buffer
211
. The output buffer
211
comprises a plurality of npn transistors TrC
1
to TrC
4
made in silicon. The logic circuit
210
converts the input signal Vpc supplied from a DA converter (not shown in the figure) according to the signal level of input signal Vmod, and outputs either signal V
900
or V
1800
through output buffer
211
. The bias switching circuit
203
thus outputs signal V
900
or V
1800
to select a particular power amplifier and controls the signal level of the output signal from the selected power amplifier based on input signal Vpc, and stops operation of the other (unselected) power amplifier regardless of input signal Vpc.
It is to be noted that while the first biasing circuit
201
and second biasing circuit
202
shown in
FIG. 10
are made with silicon elements, those shown in FIG.
12
A and
FIG. 12B
are made using HBT as known from the literature. The biasing circuit shown in
FIG. 12A
can compensate for a change in the base-emitter voltage Vbe according to the temperature coefficient of the power amplification HBT in
FIG. 10
by means of transistor TrD
2
, as can the biasing circuit shown in
FIG. 12B
using transistors TrD
2
and TrD
3
.
It is to be noted that all transistors TrD
1
to TrD
3
in
FIGS. 12A and 12B
are HBTS, and either signal V
900
or V
1800
in
FIG. 11
can be applied to either biasing circuit through the biasing circuit input terminal Vin.
Unlike an FET, however, an HBT operates by amplifying the base current, and requires a base current supply between several 10 to 100 mA to achieve the high 2 W to 4 W output of a GSM phone. It is, however, also difficult to directly obtain such a high base current from a standard Si-CMOS IC because the output current used to assure a specific output voltage from a standard CMOS device is a maximum of several milliamperes.
Furthermore, two power amplifiers can be easily controlled using input signals Vpc and Vmod due to the general utility of the logic circuit design when silicon elements are used in the bias switching circuit, but a separate control circuit using silicon elements is required for controlling devices other than the HBT power amplifier.
When silicon elements are used in the bias switching circuit and biasing circuits, or just the bias switching circuit, these circuits cannot be integrated to an MMIC comprising HBTs. A separate silicon chip is therefore needed, and this reduces yield during mass production.
SUMMARY OF THE INVENTION
With consideration for the aforementioned problems, an object of the present invention is to provide a dual band system high frequency power amplifier that can be integrated with an MMIC comprising HBTs by using HBTs to form the biasing circuits and bias switching circuit of each dual band system high frequency power amplifier comprising HBTs.
To achieve this object, a high frequency power amplifier according to the present invention has two power amplifiers each having at least one power amplifying heterojunction bipolar transistor (HBT), two biasing circuits each disposed for each power amplifier and including a HBT, and a bias switching circuit for exclusively switching operation between the biasing circuits in accordance with first and second signals input to the bias switching circuit. The bias switching circuit of the high frequency power amplifier has a first switching circuit including an HBT for controlling output of the first signal for controlling biasing circuit operation to one of the biasing circuits; a second switching circuit including an HBT for controlling output of the first signal to an other biasing circuit; and a third switching circuit including an HBT for controlling operation of the second switching circuit according to the second signal for controlling operation of the first switching circuit to exclusively select and operate the first and second switching circuits.
The bias switching circuit for switching operation of biasing circuits constructed with HBTs thus has a first switching means for controlling output to one biasing circuit, a second switching circuit for controlling output to another biasing circuit, and a third switching circuit for exclusively selecting the first or second switching circuit to operate. The first to third switching means of the bias switching circuit are made using common AlGaAs or GaAs HBTs, three or more of which are connected in series so that the total combined base-emitter voltage Vbe does not exceed 3 V. The bias switching circuit can therefore operate reliably even in low 3-V power supply systems, and can thus be integrated with an HBT MMIC to simply the manufacturing process.
The first and second switchin
Choe Henry
Leydig Voit & Mayer Ltd
Mitsubishi Denki & Kabushiki Kaisha
Pascal Robert
LandOfFree
High frequency power amplifier does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High frequency power amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High frequency power amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2565984