Philips Semiconductors Linear Products

Product specification

NE/SE531

High slew rate operational amplifier

August 31, 1994

77

CYCLIC A-TO-D CONVERTER

One interesting, but much ignored, A/D converter is the cyclic

converter. This consists of a chain of identical stages, each of which

the input and doubles the remainder if the polarity was correct. In

Figure 1, the signal is full-wave rectified and the remainder of

equivalent of the input voltage in digitized form related to the

using NE531 devices settles in 5

µs.

TRIANGLE AND SQUARE WAVE GENERATOR

The circuit in Figure 2 will generate precision triangle and square

waves. The output amplitude of the square wave is set by the output

swing of op amp A-1, and R1/R2 sets the triangle amplitude. The

frequency of oscillation in either case is:

f

+

1

4RC

@

R2

R1

(1)

The square wave will maintain 50% duty cycle even if the amplitude

of the oscillation is not symmetrical.

The use of the NE531 in this circuit will allow good square waves to

be generated to quite high frequencies. Since the amplifier A1 runs

open-loop, there is no need for compensation. The

triangle-generating amplifier must be compensated. The NE5535

device can be used as well, except for the lower frequency

response.

a.

b.

+vcc

10K

LOGIC OUT

NE531

+

–

10K

2K

VREF

NE531

+

–

20K

20K

VOUT

VREF

–VIN

LOGOUT

VIN

VREF

VREF

VIN

0

Figure 1. Cyclic A-to-D Converter