12

LT1394

Figure 12. Voltage-Controlled Delay’s Waveforms.

Programming Voltage Determines Delay Between Input

(Trace A) Falling Edge and Output (Trace D) Rising Edge.

High Linearity Timing Ramp (Trace B) Permits 1ns

Accuracy and 100ps Repeatability

10ns/DIV

1394 F13

Figure 13. High Speed Expansion of Figure 12. Ramp

(Trace B) Begins When Trigger (Trace A) Falls and

Current Source Turns On (Trace C). Trace D is Output

10ns/DIV

1394 F14

B = 1V/DIV

C = 0.1V/DIV

D = 1V/DIV

A = 1V/DIV

Figure 14. Delay’s Output Switching Begins with

Trigger Falling Low (Trace A). Ramp (Trace C) Starts

3ns After Current Source Turn-On (Trace D). Output

(Trace B) Begins 4ns Later

C = 5V/DIV

D = 5V/DIV

B = 2V/DIV

A = 5V/DIV

100ns/DIV

1394 F12

A = 2V/DIV

B = 0.1V/DIV

C = 2V/DIV

D = 2V/DIV

delay programming voltage. The fast switching and ramp

linearity permits 1ns accuracy and 100ps repeatability.

Figure 13, a high speed expansion of the current source

turn-on, details the clean switching. Q4 goes off within 2ns

of the trigger input (Trace A) dropping low, enabling the

current source (Q2’s emitter is Trace C). Concurrently, the

1000pF capacitor’s ramp (Trace B) begins. The LT1394’s

output (Trace D) drops low about 7ns later, returning high

after crossing (in this case) a relatively low programming

voltage. Figure 14 juxtaposes the waveforms differently,

permitting enhanced study of circuit timing. Switching

begins with the input trigger falling low (Trace A). The ramp

(Trace C) begins 3ns after the current source turns on (Q2

emitter is Trace D). The output pulse (Trace B) begins

about 4ns later.

To calibrate this circuit apply a trigger input and 3V to the

programming input. Adjust the 100

Ω trim for a 300ns

width at the LT1394’s output.

–

+

LT1394

5V

0.1

µF

1394 F11

DELAY PROGRAMMING

VOLTAGE INPUT

0V TO 3V = 0 TO 300ns DELAY

1000pF

TRIGGER INPUT

200ns MINIMUM

1k

330

Ω

330

Ω

100

Ω

LT1634

PNP = 2N5087

NPN = 2N2369

220

Ω

100

Ω

(DELAY

CALIB)

51pF

0.1

µF

Q1

Q2

Q OUTPUT

Q OUTPUT

Q4

Q3

Figure 11. Fast, Precise, Voltage-Controlled Delay.

Emitter Switched Current Source Has Clean,

Predictable Dynamics