Additional Applications of the LM1203
(Continued)
When diode D4 at Pin 11 is switched to ground the input
video signals will be DC shifted down and clamped at a
voltage near ground (approximately 250 mV) This will dis-
able the video amplifiers and force the output DC level low
The DC outputs from other similarly configured LM1203s
could overide this lower DC level and provide the output
signals to the 75X cable drivers In this case any additional
LM1203s would share the same 390X output resistor The
maximum DC plus peak white output voltage should not be
allowed to exceed 7V because the ‘‘off’’ amplifier output
stage could suffer internal zener damage See
Figure 3
and
text for a description of the internal configuration of the vid-
eo amplifier
Figure 10
shows the configuration for a three channel high
frequency amplifier with non gated DC feedback Pin 14 is
tied low to turn on the clamp comparators (feedback amplifi-
ers) The inverting inputs (Pins 17 21 26) are connected to
the amplifier outputs from a low pass filter Additional low
frequency filtering is provided by the clamp caps The drive
resistors can be made variable or fixed at values between 0
and 300X Maximum output swings are achieved when the
DC output is set to approximately 4V The high frequency
response will be dependent upon external peaking at the
drive pins
TL H 9178 – 10
FIGURE 10 Three Channel High Frequency Amplifier with Non-gated DC Feedback (Non-video Applications)
http
www national com
12
NSC [ NATIONAL SEMICONDUCTOR ]
