Telecommunications – Transmitter – Power control – power supply – or bias voltage supply
Reexamination Certificate
2001-09-19
2004-11-02
Ramakrishnaiah, Melur (Department: 2643)
Telecommunications
Transmitter
Power control, power supply, or bias voltage supply
C455S552100, C455S553100
Reexamination Certificate
active
06813480
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of radio communications. More specifically, the present invention relates to a transmitter architecture utilizing a voltage controlled attenuator to control its transmission signal level.
BACKGROUND OF THE INVENTION
A new generation of radiotelephones is expected to be more capable and more efficient than a previous generation of radiotelephones. Such new radiotelephone may be expected to allow a user to operate in multiple systems that were traditionally incompatible such as time-division-multiple-access (TDMA), global system for mobile (GSM), and code-division-multiple-access (CDMA), while providing a longer talk time without increasing in size. In order to support multiple systems, the radiotelephone is likely to be required to support multiple radio frequency (RF) bands such as 800 MHz, 900 MHz, 1800 MHz, and 1900 MHz.
A voltage controlled attenuator (VCA) is an essential part of today's transmitter architecture providing a strict control of a transmission signal level required by the systems. A common differential VCA
100
consists of a differential amplifier
102
and a steering block
104
as illustrated in FIG.
1
. The signal level at the output
106
and
108
of the VCA is varied by applying a differential control voltage (V
c
) to the steering lines
110
and
112
which are connected to the bases of transistor pair
114
and
116
, and to the bases of transistor pair
118
and
120
, respectively. The control voltage steers the current flow between
114
and
118
, and between
116
and
120
. For a maximum output power, a maximum differential control voltage is applied to the steering lines
110
and
112
with the line
110
having a lower voltage and the line
112
having a higher voltage relative to each other respect to a circuit ground. All of the current available from the power supply line
130
flows through loads
122
and
124
, and a differential RF input signal present on lines
126
and
128
is amplified. For a minimum power, a maximum differential control voltage is applied to the steering lines
110
and
112
with the line
110
having a higher voltage and the line
112
having a lower voltage relative to each other respect to a circuit ground. The current available from the power supply line
130
is allowed to flows through transistor pair
114
and
116
thereby reducing the current flow through loads
122
and
124
and attenuating the differential RF input signal.
In order to support multiple bands, today's common transmitter architecture employed in a radiotelephone uses a VCA followed by an external switch to select one of the multiple bands, or uses multiple VCAs dedicating one VCA for each band as illustrated. However, each of these methods has disadvantages.
The external switch method requires an additional component, namely a separate switch device. Because of system requirements for high linearity for high power signal, the switch device must achieve high linearity requiring large current drain, and the signal going through the switch device experiences some loss which degrades the signal quality. The through-loss of the switch device must be compensated with a higher gain, which requires more current drain, somewhere in the transmitter lineup in order to achieve a desired power output. The external switch device also requires an additional space on the radiotelephone printed circuit board making the radiotelephone larger.
The multiple VCA method does not degrade the signal quality. However, integrating multiple VCA circuits into a single device increases the die size of the device and increases parts required to support such circuits.
Accordingly, there is a need to control an output power level of a radio frequency (RF) signal and to direct the RF signal to an appropriate path for a multi-mode and multi-band radiotelephone without using an external switch and without using multiple common VCAs.
REFERENCES:
patent: 5802452 (1998-09-01), Grandfield et al.
patent: 5862460 (1999-01-01), Rich
patent: 5995853 (1999-11-01), Park
patent: 6038428 (2000-03-01), Mizusawa et al.
patent: 6226114 (2001-05-01), Ashkeboussi et al.
Balasubramaniyan Arul
Losser Daniel Eric
Nobbe Dan
Motorola Inc.
Ramakrishnaiah Melur
Shigeharu Furukawa
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