Datasheet LT1719 (Analog Devices) - 22

LT1719
TYPICAL APPLICATION High Performance Sine Wave
from 0dBm to 15dBm. If a 2:1 transformer is used to drive
to Square Wave Converter
the input differentially, this exceptionally fl at zone spans Propagation delay of comparators is typically specifi ed for –5dBm to 10dBm, a common range for RF signal levels. a 100mV step with some fraction of that for overdrive. But Similar delay performance is achieved with input frequen- in many signal processing applications, such as in com- cies as high as 50MHz. There is, however, some additional munications, the goal is to convert a sine wave, such as encroachment into the central fl at zone by both the small a carrier, to a square wave for use as a timing clock. The amplitude and large amplitude variations. desired behavior is for the output timing to be dependent With small input signals, the hysteresis and dispersion on the input timing only. No phase shift should occur as make the LT1719 act like a comparator with a 12mV a function of the input amplitude, which would result in hysteresis span. In other words, a 12mV AM to FM conversion. P-P sine wave at 10MHz will barely toggle the LT1719, with 90° of phase The circuit of Figure 9a is a simple LT1719S8-based sine lag or 25ns additional delay. wave to square wave converter. The ± 5V supplies on the Above 5V input allow very large swing inputs, while the 3V logic P-P at 10MHz, the LT1719 delay starts to decrease due to internal capacitive feed-forward in the input stage. supply keeps the output swing small to minimize cross Unlike some comparators, the LT1719 will not falsely an- talk. Figure 9b shows the time delay vs input amplitude ticipate a change in input polarity, but the feed-forward is with a 10MHz sine wave. The LT1719 delay changes just enough to make a transition propagate through the LT1719 0.65ns over the 26dB amplitude range; 2.33° at 10MHz. faster once the input polarity does change. The delay is particularly fl at yielding excellent AM rejection 5 5V 3V SINE WAVE 4 INPUT + SQUARE WAVE OUTPUT 25°C VCC = 5V 50Ω LT1719S8 3 VEE = –5V – +VS = 3V 10MHz 2 –5V TIME DELAY (ns) 1719 F09a 1 632mVP-P 2VP-P 6.32VP-P
Figure 9a. LT1719-Based Sine Wave to Square Wave Converter
0 –5 0 5 10 15 20 25 INPUT AMPLITUDE (dBm) 1719 F09b
Figure 9b. Time Delay vs Sine Wave Input Amplitude RELATED PARTS PART NUMBER DESCRIPTION COMMENTS
LT1016 UltraFast Precision Comparator Industry Standard 10ns Comparator LT1116 12ns Single Supply Ground-Sensing Comparator Single Supply Version of LT1016 LT1394 7ns, UltraFast, Single Supply Comparator 6mA Single Supply Comparator LT1671 60ns, Low Power, Single Supply Comparator 450μA Single Supply Comparator LT1713/LT1714 Single/Dual 7ns, Rail-to-Rail Comparator Rail-to-Rail Inputs and Outputs LT1720/LT1721 Dual/Quad 4.5ns, Single Supply 3V/5V Comparator Dual/Quad Comparator Similar to the LT1719 1719fa 22 Linear Technology Corporation LT 0809 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2000