Browse Prior Art Database

Analog Scaler for a Multi-Media System

IP.com Disclosure Number: IPCOM000103858D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Fleischman, RM: AUTHOR [+3]

Abstract

Disclosed is a circuit for changing the size of a video image, so that, for example, a smaller image may be displayed as a window in a larger image from a different video channel. The type of design referred to as an integrate, hold, and dump circuit is used for this purpose.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Analog Scaler for a Multi-Media System

      Disclosed is a circuit for changing the size of a video image,
so that, for example, a smaller image may be displayed as a window in
a larger image from a different video channel.  The type of design
referred to as an integrate, hold, and dump circuit is used for this
purpose.

      As shown in the figure, the circuit includes a horizontal
functional block 2 and a vertical functional block 4, which operate
with external circuits such as system processor 6, frame memory
controller 8, and frame memory 10.

      Within horizontal function block 2, programmable gain amplifier
12, to which a video signal is applied as an input, has an adjustable
gain which is set by the controller 14, being integrally linked with
the scaler sample rate and scale ratios set up by controller 14.
Each specific scale ratio adjusts the output amplitude of integrator
16 to remain constant, with a constant input voltage, over the
variable range of sample periods.  Without this correction, the
output of integrator 16 would reduce as the sample period is reduced,
and the brightness of the scaled image would vary from that of the
full size image.

      Alternately, a relative measurement of the intensity of the
smaller image in the window, compared with the intensity of the image
on the remaining portion of the screen, can be used to provide a
relative gain set correction as well a correction of the change in
brightness due to the scale ratio.

      Integrator 16 is a typical design, except that internal analog
switches have been added, enabling it to operate more like an
integrate, hold, and dump circuit.  These additional internal
switches permit the input signal to be disconnected for a period of
time, so that the output of integrator 16 will remain constant while
it is saved in analog line memory 18.

      Switc...