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

TLH9178 – 10

FIGURE 10 Three Channel High Frequency Amplifier with Non-gated DC Feedback (Non-video Applications)

http

www nationalcom

12