Amplifiers – Signal feedback – In cascade amplifiers
Reexamination Certificate
1999-09-28
2001-01-16
Pascal, Robert (Department: 2817)
Amplifiers
Signal feedback
In cascade amplifiers
C330S099000, C330S288000
Reexamination Certificate
active
06175275
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an amplifier with an adjustable bandwidth suitable for preamplifying a video signal in CRT displays.
DISCUSSION OF THE RELATED ART
Video preamplifiers are used to process RGB video signals and to provide them to a power video amplifier that directly drives the cathodes of the tube. The processing applied to the video signals is mainly the amplification of the signal to adjust the picture contrast, the DC level adjustment in order to control the picture brightness, and the insertion of on-screen display signals in the video signal.
FIG. 1
represents a conventional video preamplifier. It comprises a transconductance circuit
2
connected to receive an input voltage VIN, followed by an adjustable gain stage
4
and a DC level stage
6
, controlled by an external circuit such as a microprocessor
8
. An NPN output transistor
10
is connected between a power supply terminal, and a reference terminal such as ground through a current source
12
. The base of the transistor
10
is connected to an output terminal of circuit
6
, and a resistor
14
connects the base of transistor
10
to ground. The output
16
of the preamplifier is taken at the emitter of transistor
10
.
Transistor
10
acts as a voltage follower with a short rise time. The rise and fall times of transistor
10
determine the bandwidth of the preamplifier.
It is important to note that the connections between a preamplifier and the power amplifier that follows comprise parasitic inductances. Parasitic inductances usually give birth to important voltage overshoots when receiving signals that feature short rise and fall times. Therefore, special care must be taken for connecting a preamplifier with short rise and fall times to a power amplifier, in order to reduce these parasitic inductances.
For cost reduction reasons, preamplifier manufacturers tend to produce only a single type of preamplifier that features a large bandwidth, suited for high quality displays. Lower quality displays may use these preamplifiers, but it becomes necessary in these displays to improve the connections between the preamplifier and amplifier in order to reduce the parasitic inductance, which increase the design cost.
An object of the invention is to provide a single type of preamplifier which will provide satisfactory results both in high and low quality displays.
SUMMARY OF THE INVENTION
To achieve this object, the invention provides a preamplifier that comprises an output stage having a bandwidth which is adjustable by a control signal.
More specifically, the output stage comprises an amplifier with an adjustable bandwidth. The amplifier comprises a main input for receiving an input current, a main output for providing an output voltage, a resistor connected between the main input and output. A current amplifier with an adjustable gain is connected for receiving the input current. A capacitor is connected between an output of the current amplifier and the main output. An inverting transconductance circuit is connected between the output of the current amplifier and the main output.
The foregoing and other objects, features, aspects and advantages of the present invention will be discussed in detail in the following description of specific embodiments, taken in conjunction with the accompanying drawings, but not limited by them.
REFERENCES:
patent: 3127565 (1964-03-01), Williams
patent: 3252105 (1966-05-01), Patchell
patent: 3304506 (1967-02-01), Weekes
patent: 3392345 (1968-07-01), Young
patent: 3678416 (1972-07-01), Burwen
patent: 5007038 (1991-04-01), Nakane et al.
Barou Michel
Chaussy Danika
Choe Henry
Galanthay Theodore E.
Morris James H.
Pascal Robert
STMicroelectronics S.A.
LandOfFree
Preamplifier with an adjustable bandwidth does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preamplifier with an adjustable bandwidth, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preamplifier with an adjustable bandwidth will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2478796