650Mhz amplifying prescaler probe
Posted on Nov 14, 2012 11081
The 650 MHz Prescaler Probe's input is terminated by resistor Rl and is fed through Cl to the diode limiter composed ofD1 through D4. Those diodes are forward-biased by the +5 volt supply for small-input signals and, in turn, feed the signal to Ul. However, for larger input signals, diodesD1 through D4 will start to turn off, passing less of the signal, and, thus, attenuating it. But even in a full-off state, the FHllOO-type diodes will always pass a small part of the input to Ul because of capacitive leakage within the diodes. Integrated circuit Ul, a Plessey SL952 bipolar amplifier, capable of 1 GHz operation, provides 20 to 30 dB of gain.
The input signal is supplied to pin 10, Ul with the other input (pin 11) is bypassed to ground. The output signal is taken at pin 3 and pin 4, with pin 3 loaded by R4 and pin 4 by R5. Integrated circuit 11C90, U2, is a high-speed prescaler capable of 650 MHz operation configured for a divide-by-10 format. A reference voltage internally generated appears at pin 15 and is tied to pin 16, the clock input. This centers the capacitive-coupled input voltage from Ul around the switching threshold-voltage level. An ECL-to-TTL converter in Ul provides level conversion to drive TTL input counters by typing pin 13 low. Therefore, no external ECL to TTL converter is required at the pin 11 output. On the other hand, ECL outputs are available at U2, pin 8 (Q4) and at pin 9 (Q4), if desired. In that circuit configuration, pin 13 is left open, and U2 will use less power.