AD652

REV. B

–16–

Figure 30. Delta Modulator lnput Signal and Ramp-Wise

Approximation

Figure 31. Delta Modulator Input Signal, Ramp-Wise

Approximation and Output Frequency

Figure 32. Maximum Integrating Cap Value vs. Input

Signal Bandwidth

BRIDGE TRANSDUCER INTERFACE

The circuit of Figure 33 illustrates a simple interface between

the AD652 and a bridge-type transducer. The AD652 is an

ideal choice because its buffered 5 volt reference can be used as

the bridge excitation thereby ratiometrically eliminating the gain

drift related errors. This reference will provide a minimum of

10 mA of external current, which is adequate for bridge resis-

tance of 600

Ω and above. If, for example, the bridge resistance

is 120

Ω or 350 Ω, an external pull-up resistor (R

and can be calculated using the formula:

=

5 V

– 10 mA

An instrumentation amplifier is used to condition the bridge sig-

nal before presenting it to the SVFC. The AD625, with its high

CMRR, minimizes common-mode errors and also can be set to

arbitrary gains between 1 and 10,000 via three resistors, simpli-

fying the scaling for the AD652’s calibrated 10 volt input range.

These resistors should be selected such that the following equa-

tion holds:

10 V

+1









where 10 k

output voltage of the bridge.

The bridge output may be unipolar, as is the case for most

pressure transducers, or it may be bipolar as in some strain mea-

surements. If the signal is unipolar, the reference input of the

AD625 (Pin 7) is simply grounded. If the bridge has a bipolar

output, however, the AD652 reference can be tied to Pin 7,

thereby, converting a

±5 volt signal (after gain) into a 0 volt to

+10 volt input for the SVFC.

Figure 33. Bridge Transducer Interface

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

Cerdip

(Q-16)

16

1

8

9

0.310 (7.87)

0.220 (5.59)

PIN 1

0.005 (0.13) MIN

0.080 (2.03) MAX

SEATING

PLANE

0.023 (0.58)

0.014 (0.36)

0.200 (5.08)

MAX

0.840 (21.34) MAX

0.150

(3.81)

MIN

0.070 (1.78)

0.030 (0.76)

0.200 (5.08)

0.125 (3.18)

0.100

(2.54)

BSC

0.060 (1.52)

0.015 (0.38)

15°

0°

0.320 (8.13)

0.290 (7.37)

0.015 (0.38)

0.008 (0.20)

PLCC

(P-20A)

3

PIN 1

IDENTIFIER

4

19

18

8

9

14

13

TOP VIEW

(PINS DOWN)

0.395 (10.02)

0.385 (9.78)

SQ

0.356 (9.04)

0.350 (8.89)

SQ

0.048 (1.21)

0.042 (1.07)

0.048 (1.21)

0.042 (1.07)

0.020

(0.50)

R

0.050

(1.27)

BSC

0.021 (0.53)

0.013 (0.33) 0.330 (8.38)

0.290 (7.37)

0.032 (0.81)

0.026 (0.66)

0.180 (4.57)

0.165 (4.19)

0.040 (1.01)

0.025 (0.64)

0.056 (1.42)

0.042 (1.07)

0.025 (0.63)

0.015 (0.38)

0.110 (2.79)

0.085 (2.16)