The EL2090 is the first complete DCrestored
monolithic video amplifier
sub-system. It contains a very highquality
video amplifier and a nulling sample-and-hold
amplifier specifically designed to stabilize video
performance. When the HOLD logic input is set to a logic 0
during a horizontal sync, the sample-and-hold amplifier may
be used as a general-purpose op-amp to null the DC offset
of the video amplifier. When the HOLD input goes to a logic
1 the sample-and-hold stores the correction voltage on the
hold capacitor to maintain DC correction during the
subsequent scan line.
The video amplifier is optimized for video characteristics,
and performance at NTSC is nearly perfect. It is a currentfeedback
amplifier, so that -3dB bandwidth changes little at
various closed-loop gains. The amplifier easily drives video
signal levels into 75Ω loads. With 100MHz bandwidth, the
EL2090 is also useful in HDTV applications.
The sample-and-hold is optimized for fast sync pulse
response. The application circuit shown will restore the video
DC level in five scan lines, even if the HOLD pulse is only
2μs long. The output impedance of the sample-and-hold is
low and constant over frequency and load current so that the
performance of the video amplifier is not compromised by
connections to the DC restore circuitry.