NTE851

The NTE851 is an integrated circuit prescaler in a 14Lead DIP type package intended for use in TV frequency synthesis tuning systems over an input frequency range of 90 to 1000MHz. It performs division by 256 in he UHF mode and division by 64 in the VHF mode.

The mode of operation of NTE851 can be selected by means of the bandswitch and the separate UHF and VHF input pins provided. The output is a complementary emittercoupled stage with controlled slew rate for harmonic suppression.

All input pins of NTE851 should be AC coupled to the appropriate input signal source. Because of high sensitivity, unbuffered coupling from the local oscillator is possible in most cases. In the UHF mode, which is activated by applying a high level to the bandswitch input pin, all eight divider stages are operative, resulting in division by 256. In the VHF mode, activated by a low level at the VHF input pin, two divider stages of NTE851 are bypassed, resulting in division by 64. As a result, approximately the same range of output frequencies are generated fo both the UHF and VHF TV bands. An internal amplifier/multiplexer provides this control while isolating both inputs and amplifying the VHF signal. In addition, hrmonic output of NTE851 is reduced above 40MHz by limiting output signal rise and fall times and maintaining a balanced load.