Droop compensation circuitry

Details Droop compensation circuitry Droop compensation circuitry

2001-09-28

2003-12-09

Berhane, Adolf D. (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

Reexamination Certificate

active

06661214

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a regulator used to regulate the input voltage to transistor-based loads, such as to RF preamplifiers or RF amplifiers employed to drive solid state pulsed radar transmitters.
BACKGROUND OF THE INVENTION
Voltage regulators are used in a variety of contexts for providing and regulating the voltage applied to electronic circuit devices. Just by way of example, voltage regulators are an important system component in solid-state pulsed radar systems. In that context, voltage regulators are used to regulate the voltage supplied to various loads such as preamplifiers or amplifiers that power the radar transmitter circuitry.
One common problem with linear voltage regulators is that their voltage output will tend to decrease during loading (e.g., during transmit gate pulses) until the regulator senses the error and begins to regulate the output voltage. This decrease is sometimes referred to as “droop.” Generally, this problem is attributable to the voltage regulator output capacitance droop (dV=1/C*Idt). In the context of a pulsed radar system, this droop in the output voltage causes a decrease in the RF transistor power output. This results in suboptimal system performance.
This problem of a decrease in the RF transistor output may worsen in systems having multiple cascaded stages, such as in a solid-state radar system with cascaded amplifiers. Accordingly, the performance loss accumulates.
Additionally, it is common that RF transistor-based circuits will tend to exhibit their own natural droop over the course of a powering cycle. For example, high (e.g., microwave) frequency RF transistor-based circuitry in a pulsed radar system will tend to exhibit a droop in gain that worsens over the course of the transmit pulse. This may be attributable to heating of the RF transistor junction during an RF pulse, which, in turn, may cause a decrease in the transistor output power during the RF transmit pulse. The RF output power is no longer constant throughout the RF pulse, resulting in suboptimal performance.
When a voltage regulator exhibiting its own droop is used with a transistor-based circuit having its own internal droop, the overall performance loss exacerbates. That is, the droop in the regulator output voltage causes a decrease in the RF transistor power output, thereby adding to an already decreasing output power that is caused by the characteristics of the RF transistor.
Conventional voltage regulators, such as linear regulators in the prior art, may suffer the aforementioned drawbacks. In a linear regulator, the voltage is typically preset to a predetermined voltage (“reference voltage”) for normal operation. In some cases this reference voltage is adjustable so that a more accurate output voltage can be established when the load is applied. Otherwise, in a typical linear voltage regulator, the reference voltage does not change once it is set. Accordingly, the linear regulator output voltage may decrease during load pulses due to the droop in the output capacitor voltage.
FIG. 1
illustrates a conventional linear regulator circuit. Typical linear regulators may be “off-line” or “on-line.” An off-line linear regulator will tend to have a smaller input capacitance and a larger output capacitance. An on-line regulator tends to have larger input capacitance and a smaller output capacitance. Both types will tend to exhibit the problems discussed above.
FIG. 2
is an illustration (not to scale) of an example of the problem of internal transistor droop. In
FIG. 2
, graph A represents an ideal regulator output voltage, where the regulator output voltage is constant and is without droop. Graph B represents the output of a transistor-based circuit that is regulated by the ideal regulator output voltage. As can be seen, over the course of a gate pulse the transistor-based circuit exhibits an increasing transistor droop
200
. Once again, this may be attributable to heating of the RF transistor junction during an RF pulse, which, in turn, may cause a decrease in the transistor output power during the RF transmit pulse. The RF output power is no longer constant throughout the RF pulse, resulting in suboptimal performance.
FIG. 3
is an illustration (not to scale) of an example of the problem of regulator droop in conjunction with load transistor droop. In
FIG. 3
, graph A represents a regulator output voltage (e.g., a linear regulator with an output capacitance) that exhibits a regulator droop
300
over the course of a gate pulse. This regulator droop
300
aggregates or combines with the load transistor's internal droop to render an even greater overall amplifier output droop
350
. This represents that a further degraded system-level performance when compared to FIG.
2
. Not only is the power output of
FIG. 3
not constant over time (like FIG.
2
), but the average power output of
FIG. 3
is even less than that of FIG.
2
. This is a significant drawback.
In sum, so-called “real world” voltage regulators used with real world transistor-based circuits tend to suffer significant performance losses associated with regulator droop and/or load transistor droop. In high stability systems, like solid state pulsed radar systems, these performance losses can be a significant problem. This problem can be mitigated somewhat by using custom transistors (or by screening commercial-off-the-shelf [COTS] transistors), but this may greatly increase the costs of production. In many markets, such as for low- to medium-production military applications, these cost increases may not be acceptable.
Finally, it can be readily appreciated that the problem of voltage droop exists in other contexts. For example, instead of an RF transistor load for the regulator, there may be some other component, device, or system, whose output response (e.g., voltage, gain, power, etc.) exhibits some undesirable variation over time. Also, the variation of this output response or gain may increase over some time period, decrease over some time period, or increase and decrease at points over a time period. The common problem is that of how to control (or compensate for) the time variable output response in order to render the desired output response. Generally, the desired output response is constant or flat over some period of time for the system at issue. Sometimes, a non-flat response may be desired.
Other problems and drawbacks also exist.
SUMMARY OF THE INVENTION
An embodiment of the present invention comprises a voltage regulator including a droop compensation circuit and a voltage regulator circuit. The droop compensation circuit compensates for an output that changes over a period of time. This variable output may be the result of voltage regulator droop and/or a load transistor droop. For instance, the voltage regulator droop may be associated with the decrease in regulator output voltage that occurs during the course of applying a load. The load transistor droop may correspond to the decrease in RF transistor gain that occurs over the course of a transmit pulse. The variable output could be attributable to other phenomena. Moreover, the variable output that is compensated for is not necessarily decreasing over time, but, in fact, could be increasing over time, or could exhibit increases and decreases over time.
The voltage regulator of the present invention may be used to regulate the voltage supplied to a preamplifier circuit or an amplifier circuit. The droop compensation circuit may include a control circuit, an offset circuit, and a discharge circuit. The droop compensation circuit may be designed to render a desired output response of the preamplifier circuit or the amplifier circuit. According to one aspect of the invention, the desired output response is substantially flat over the course of a transmit cycle. According to another aspect of the invention, the desired output response is not flat over the course of a transmit cycle. The transmit cycle may correspond to the transmit cycle of a pulsed radar system. The voltage re

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