Electricity: power supply or regulation systems – Output level responsive
Reexamination Certificate
2002-10-15
2004-06-29
Patel, Rajnikant B. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
C323S282000, C455S572000
Reexamination Certificate
active
06756773
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to switching mode power supplies for a pulsed load, in particular for a TDD, TDMA, Cellular, Cordless Telephony, and Telematics systems.
BACKGROUND OF THE INVENTION
Contemporary communication systems use one communication channel for more than one user at a time (time, code or frequency domain multiplexing), and for more than one direction of communication at a time (time or frequency domain duplexing). This causes the mobile unit of the communication system to consume different currents during different time phases of the communication cycle, typically Idle, Tune, Receive and Transmit.
As a result, battery consumption is bursty, there being prolonged periods of minimal battery consumption followed by bursts of high current drain.
In order to guarantee communication stability of the communication link during the burst, it is desirable to smooth power supply voltage such that frequency and timing of signals are not changed significantly on the both sides of the communication link due to voltage change caused, in turn, by current consumption change. It has been proposed in the art to smooth transmitter drain during bursts of signal transmission. For example, US20020072399 (Fritz) published Jun. 13, 2002 and entitled “Voltage controller for a pulsed load, in particular for a mobile-telephone or telematics transmitter” discloses a voltage controller for a pulsed load, in particular for a mobile telephone or telematics transmitter. In order to maintain constant power of the load, in particular the transmission power, a control element is connected between an input connection of the voltage controller and an output connection for supplying an output voltage to a pulsed load. A comparator compares an actual value signal corresponding to the output voltage with a desired reference value signal and supplies a control signal to the control element in order to adapt the actual value signal to the desired value signal. A desired value circuit derives the desired reference value signal from the input voltage in such a way that it is substantially constant over the duration of a load pulse. This is typical of feedback circuits that compare the actual voltage to a desired reference voltage and then apply error correction to adjust the output voltage.
It is also well known in the literature to use switched mode power supplies (SPMS) also known as voltage converters such as boost and buck converter circuits for step-up and step-down voltage conversion, respectively. U.S. Pat. No. 5,998,977 (Hsu et al.) published Dec. 7, 1999 and entitled “Switching power supplies with linear precharge, pseudo-buck and pseudo-boost modes” discloses a variety of startup modes for operating a boost type switching power supply. A linear charging mode couples the input voltage directly to the output voltage, thereby pre-charging the output capacitor of the switching power supply. The linear mode serves to reduce inrush battery current and limit the stress voltage on the power switching devices. A pseudo-buck mode, preferably entered into after the linear mode has pre-charged the output capacitor, operates the boost type switching power supply in a manner providing power to the output essentially as a buck type switching power supply would. This results in continuous charging of the output capacitor, thereby reducing startup time and increasing power efficiency.
FIG. 1
shows schematically a boost voltage converter
10
comprising a switching circuit depicted generally as
11
having an input
12
and an output
13
. The switching circuit
11
includes an inductor
14
coupled between the input
12
and the output
13
via a Schottky diode
15
. A MOSFET
16
has its drain coupled to the junction between the inductor
14
and the Schottky diode
15
, and its source connected to GND. The gate of the MOSFET
16
is controlled by a controller
17
(constituting a voltage controller) that is also coupled to the output
13
so as to be responsive to the output voltage. An output filtering capacitor
18
is connected between the output
13
and GND. The controller
17
continuously monitors the voltage at the output
13
, comparing it to an internal or external reference voltage source (not shown) and sending a corresponding control signal to the MOSFET
16
, which serves as a switching element.
In
FIG. 2
there is shown schematically a buck voltage converter
20
, which uses similar components to the boost converter
10
shown in FIG.
1
and will therefore be described briefly using identical reference numerals. Thus, the buck
4
converter
20
comprises a switching circuit depicted generally as
11
having an input
12
and an output
13
. The switching circuit
11
includes an inductor
14
coupled between the input
12
and the output
13
via a MOSFET
16
whose drain is coupled to the inductor
14
and whose source is connected to the input
12
. A Schottky diode
15
is connected with its cathode between the junction between the MOSSES
16
and the inductor
14
and its anode to GND. The gate of the MOSFET
16
is controlled by a controller
17
that is also coupled to the output
13
so as to be responsive to the output voltage. An output filtering capacitor
18
is connected between the output
13
and GND. The controller
17
continuously monitors the voltage at the output
13
, comparing it to an internal or external reference voltage source (not shown) and sending a corresponding control signal to the MOSFET
16
which serves as a switching element.
In both cases, when the MOSFET
16
is conducting, current flows via the MOSFET
16
through the inductor
14
, thereby accumulating in the inductor energy that is discharged when the MOSFET
16
is cutoff and charges the capacitor
18
via the Schottky diode
15
. Such a method is based on so-called feedback correction and does not allow for a utilization of the existing in-system knowledge about an upcoming cycle pulse load change. The very nature of such a method is based on the presence of constant error of the output voltage, in order to allow the voltage controller to realize that such an error exists and try to correct it. Moreover, such an approach is very sensitive to the timing parameters of the regulated circuit and frequently causes some oscillations due to over- or under-regulation of the output voltage, due to method of regulation, after every sharp change of the load current.
The need for two types of voltage converters is derived from a need to increase the input voltage to a higher level (Boost converter) or to decrease the input voltage to a lower level (Buck converter).
FIG. 3
shows functionally a conventional pulse load system
30
such as TDD (Time Domain Duplexing), TDMA (Time Domain Multiple Access), different Cellular (TDMA, CDMA, GSM and 3G standards), Cordless telephony (FHSS, DSS, TDD) and Telematics (remote utility metering). The system
30
utilizes either of the voltage converters
10
or
20
as a standalone, independently working circuit. The voltage converter
10
, for example, supplies the power voltage to a Baseband controller
31
and an RF circuit
32
.
The Baseband controller
31
is a standard component in such systems and supervises the digital data processing required for radio transmission. This includes speech coding, encryption, packetization, error detection and correction for both the packet header and the payload data streams, sometimes signal spreading and de-spreading and/or frequency hopping. Thus, among the various tasks performed by the Baseband controller, is the control of the cycle phase of the RF circuit
32
(like Receive, Idle, Tune or Transmit).
FIG. 4
shows graphically typical power consumption during the transmit-receive cycle of TDMA system. Thus, during idle periods of the cycle there may be minimal baseline power consumption, corresponding with no need to transmit or receive any signal, typically during this time other system can transmit their signal. When it is required to transmit, the RF circuit
32
is first turned on to be tuned to the required
Koretsky Victor
Michael Nir
Berkowitz Marvin C.
D.S.P. Group Ltd.
Nath & Associates PLLC
Patel Rajnikant B.
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