9

LT1671

Figure 5 is a very versatile stage. It features a bipolar swing

that is set by the output transistor’s supplies. This 3ns

delay stage is ideal for driving FET switch gates. Q1, a

gated current source, switches the Baker-clamped output

transistor, Q2. The heavy feedforward capacitor from the

OUTPUT = 0

→ +V (TYPICALLY 3V TO 4V)

1671 F03

+V

1671 F04

1k

12pF

HP5082-2810

2N2369

2N3866

RISE TIME = 4ns

FALL TIME = 5ns

OUT

15V

–

+

1k

1k

LT1671

Figure 3. Simplified LT1671 Output Stage

Figure 4. Level Shift Has Noninverting Voltage Gain

1671 F05

OUTPUT TRANSISTOR SUPPLIES

(SHOWN IN HEAVY LINES)

CAN BE REFERENCED ANYWHERE

BETWEEN 15V AND –15V

1000pF

–10V (TYP)

1N4148

5V (TYP)

INPUT

5V

5V

–10V

–

+

0.1

µF

820

Ω

LT1671

4.7k

820

Ω

RISE TIME = 3ns

FALL TIME = 3ns

430

Ω

330

Ω

Q1

2N2907

Q2

2N2369

OUTPUT

HP5082-2810

Figure 5. Level Shift with Inverting Voltage Gain—Bipolar Swing

1671 F06

1k

12pF

2N2369

2N3866

2N5160

POWER

FET

RISE TIME = 7ns

FALL TIME = 9ns

15V

–

+

1k

1k

LT1671

Figure 6. Noninverting Voltage Gain Level Shift

LT1671 is the key to low delay, providing Q2’s base with

nearly ideal drive. This capacitor loads the LT1671’s

output transition, but Q2’s switching is clean with 3ns

delay on the rise and fall of the pulse. Figure 6 is similar to

Figure 4 except that a sink transistor has replaced the

Schottky diode. The two emitter-followers drive a power

MOSFET that switches 1A at 15V. Most of the 7ns to 9ns

delay in this stage occurs in the MOSFET and the 2N2369.

When designing level shifters, remember to use transis-

of results shown, switching times in the nanosecond