EL2157CS datasheet(15/20 Pages) ELANTEC

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EL2150CEL2157C

125 MHz Single Supply Clamping Op Amps

Applications Information

Contd

Forcing the CLAMP pin above VOP simply de-

activates the CLAMP feature In other words

one cannot expect to clamp any voltage higher

than what the EL2157C can drive to in the first

place If the clamp feature is not desired either

let the CLAMP pin float or connect it to the VSa

EL2157C Comparator Application

The EL2157C can be used as a very fast single

supply comparator by utilizing the clamp fea-

ture Most op amps used as comparators allow

only slow speed operation because of output satu-

ration issues However by applying a DC voltage

to the CLAMP pin of the EL2157C the maxi-

mum output voltage can be clamped thus pre-

venting

saturation

Figure

below

the

EL2157C implemented as a comparator 25V DC

is applied to the CLAMP pin as well as the INb

pin A differential signal is then applied between

the inputs Figure 5 shows the output square

wave that results when a g1V 10 MHz triangu-

lar wave is applied while Figure 6 is a graph of

propagation delay vs overdrive as a square wave

is presented at the input

2150 – 62

Figure 4

2150 – 63

Figure 5

EL2157 as a Comparator

Propagation Delay vs Overdrive

2150 – 64

Figure 6

Video Sync Pulse Remover Application

All CMOS Analog to Digital Converters (ADs)

have a parasitic latch-up problem when subjected

to negative input voltage levels Since the sync

tip contains no useful video information and it is

a negative going pulse we can chop it off Figure

7 shows a unity gain connected EL2150C

EL2157C Figure 8 shows the complete input vid-

eo signal applied at the input as well as the out-

put signal with the negative going sync pulse re-

moved

2150 – 65

Figure 7

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