ANALOG DEVICES AD538 Service Manual

Real-Time Analog

Computational Unit (ACU)

AD538

FEATURES

VO = VY(VZ/VX)m transfer function

Wide dynamic range (denominator) −1000:1 Simultaneous multiplication and division Resistor-programmable powers and roots No external trims required

Low input offsets <100 μV

Low error ±0.25% of reading (100:1 range) Monolithic construction

Real-time analog multiplication, division and exponentiation

High accuracy analog division with a wide input dynamic range On board +2 V or +10 V scaling reference

Voltage and current (summing) input modes Monolithic construction with lower cost and higher

reliability than hybrid and modular circuits

APPLICATIONS

Oneor two-quadrant multiply/divide

Log ratio computation

Squaring/square rooting

Trigonometric function approximations

Linearization via curve fitting

Precision AGC

Power functions

FUNCTIONAL BLOCK DIAGRAM

IX				D
25kΩ			100Ω
VX
		LOG		B
		RATIO
25kΩ				A
VZ			100Ω
IZ
+10V		INTERNAL
+2V		VOLTAGE
		REFERENCE
VY
25kΩ
IY	LOG		AD538
C		ANTILOG
I			OUTPUT	VO
				00959-001

Figure 1.

GENERAL DESCRIPTION

The AD538 is a monolithic real-time computational circuit that provides precision analog multiplication, division, and exponentiation. The combination of low input and output offset voltages and excellent linearity results in accurate computation over an unusually wide input dynamic range. Laser wafer trimming makes multiplication and division with errors as low as 0.25% of reading possible, while typical output offsets of

100 μV or less add to the overall off-the-shelf performance level. Real-time analog signal processing is further enhanced by the 400 kHz bandwidth of the device.

The overall transfer function of the AD538 is VO = VY(VZ/VX)m. Programming a particular function is via pin strapping. No external components are required for one-quadrant (positive input) multiplication and division. Two-quadrant (bipolar numerator) division is possible with the use of external level shifting and scaling resistors. The desired scale factor for both

multiplication and division can be set using the on-chip +2 V or +10 V references, or controlled externally to provide simultaneous multiplication and division. Exponentiation with an m value from 0.2 to 5 can be implemented with the addition of one or two external resistors.

Direct log ratio computation is possible by using only the log ratio and output sections of the chip. Access to the multiple summing junctions adds further to the flexibility of the AD538. Finally, a wide power supply range of ±4.5 V to ±18 V allows operation from standard ±5 V, ±12 V and ±15 V supplies.

The AD538 is available in two accuracy grades (A and B) over the industrial (−25°C to +85°C) temperature range and one grade (S) over the military (−55°C to +125°C) temperature range. The device is packaged in an 18-lead TO-118 hermetic side-brazed ceramic DIP. A-grade chips are also available.

Rev. E

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AD538

TABLE OF CONTENTS

Features ..............................................................................................	1	Stability Precautions...................................................................	10
Applications.......................................................................................	1	Using The Voltage References ..................................................	10
Functional Block Diagram ..............................................................	1	One-Quadrant Multiplication/Division..................................	11
General Description .........................................................................	1	Two-Quadrant Division ............................................................	12
Revision History ...............................................................................	2	Log Ratio Operation ..................................................................	12
Specifications.....................................................................................	3	Analog Computation Of Powers And Roots ..........................	13
Absolute Maximum Ratings............................................................	5	Square Root Operation..............................................................	13
ESD Caution..................................................................................	5	Applications Information ..............................................................	15
Pin Configuration and Function Descriptions.............................	6	Transducer Linearization ..........................................................	15
Typical Performance Characteristics .............................................	7	ARC-Tangent Approximation ..................................................	15
Theory of Operation ........................................................................	9	Outline Dimensions .......................................................................	16
Re-Examination of Multiplier/Divider Accuracy ....................	9	Ordering Guide ..........................................................................	16
Functional Description..............................................................	10

REVISION HISTORY

6/11—Rev. D to Rev. E

Updated Format..................................................................	Universal
Added Table 3....................................................................................	6
Changes to Ordering Guide ..........................................................	11
5/10—Rev. C to Rev. D
Updated Outline Dimensions .......................................................	11
Changes to Ordering Guide ..........................................................	11

Rev. E | Page 2 of 16

AD538

SPECIFICATIONS

VS = ±15 V, TA = 25°C, unless otherwise noted.

Table 1.

	Test Conditions/		AD538AD			AD538BD			AD538SD
Parameter	Comments	Min	Typ	Max	Min	Typ	Max	Min	Typ	Max	Unit
MULTIPLIER DIVIDER
PERFORMANCE
Nominal Transfer
Function
	10 V ≥ VX, VY, VZ ≥ 0	V = V (V /V )m			V = V (V /V )m				V = V (V /V )m
		O	Y Z X		O	Y Z X			O Y Z X
	400 µA ≥ IX, IY, IZ ≥ 0	V = 25 kΩ × I		(I /I )m	V = 25 kΩ × I		(I /I )m	V = 25 kΩ × I		(I /I )m
		O	Y	Z X	O	Y	Z X	O	Y	Z X
Total Error Terms	100 mV ≤ VX ≤ 10 V		±0.5	±1		±0.25	±0.5		±0.5	±1	% of Reading +
100:1 Input	100 mV ≤ VY ≤ 10 V		±200	±500		±100	±250		±200	±500	µV
Range1
	100 mV ≤ VZ ≤ 10 V
	VZ ≤ 10 VX, m = 1.0
	TA = TMIN to TMAX		±1	±2		±0.5	±1		±1.25	±2.5	% of Reading +
			±450	±750		±350	±500		±750	±1000	µV
Wide Dynamic	100 mV ≤ VX ≤ 10 V		±1	±2		±0.5	±1		±1	±2	% of Reading +
Range2
	100 mV ≤ VY ≤ 10 V		±200	±500		±100	±250		±200	±500	µV
	100 mV ≤ VZ ≤ 10 V		±100	±250		±750	±150		±200	±250	µV × (VY + VZ)/VX
	VZ ≤ 10 VX, m = 1.0
	TA = TMIN to TMAX		±1	±3		±1	±2		±2	±4	% of Reading +
			±450	±750		±350	±500		±750	±1000	µV +
			±450	±750		±350	±500		±750	±1000	µV × (VY +
											VZ)/VX
Exponent (m)	TA = TMIN to TMAX	0.2		5	0.2		5	0.2		5
Range
OUTPUT
CHARACTERISTICS
Offset Voltage	VY = 0, VC =		±200	±500		±100	±250		±200	±500	µV
	−600 mV
	TA = TMIN to TMAX		±450	±750		±350	±500		±750	±1000	µV
Output Voltage	RL = 2 kΩ	−11		+11	−11		+11	−11		+11	V
Swing
Output Current		5	10		5	10		5	10		mA
FREQUENCY
RESPONSE
Slew Rate			1.4			1.4			1.4		V/µs
Small Signal	100 mV ≤ 10 VY, VZ,		400			400			400		kHz
Bandwidth	VX ≤ 10 V
VOLTAGE REFERENCE
Accuracy	VREF = 10 V or 2 V		±25	±50		±15	±25		±25	±50	mV
Additional Error	TA = TMIN or TMAX		±20	±30		±20	±30		±30	±50	mV
Output Current	VREF = 10 V to 2 V	1	2.5		1	2.5		1	2.5		mA
Power Supply
Rejection
+2 V = VREF	±4.5 V ≤ VS ≤ ±18 V		300	600		300	600		300	600	µV/V
+10 V = VREF	±13 V ≤ VS ≤ ±18 V		200	500		200	500		200	500	µV/V
POWER SUPPLY
Rated	RL = 2 kΩ		±15			±15			±15		V
Operating Range3		±4.5		±18	±4.5		±18	±4.5		±18	V
PSRR	±4.5 V<, VS < ±18 V		0.5	0.1		0.5	0.1		0.5	0.1	%/V
	VX = VY = VZ = 1 V
	VO = 1 V
Quiescent Current			4.5	7		4.5	7		4.5	7	mA

Rev. E | Page 3 of 16

AD538

	Test Conditions/	AD538AD			AD538BD			AD538SD
Parameter	Comments	Min Typ	Max	Min	Typ	Max	Min	Typ	Max	Unit
TEMPERATURE RANGE
Rated		−25	+85	−25		+85	−55		+125	°C
Storage		−65	+150	−65		+150	−65		+150	°C

1Over the 100 mV to 10 V operating range total error is the sum of a percent of reading term and an output offset. With this input dynamic range the input offset contribution to total error is negligible compared to the percent of reading error. Thus, it is specified indirectly as a part of the percent of reading error.

2The most accurate representation of total error with low level inputs is the summation of a percent of reading term, an output offset and an input offset multiplied by the incremental gain (VY + VZ) VX.

3When using supplies below ±13 V, the 10 V reference pin must be connected to the 2 V pin in order for the AD538 to operate correctly.

Rev. E | Page 4 of 16

AD538

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter	Rating
Supply Voltage	±18 V
Internal Power Dissipation	250 mW
Output Short Circuit-to-Ground	Indefinite
Input Voltages VX, VY, VZ	(+VS − 1 V), −1 V
Input Currents IX, IY, IZ, IO	1 mA
Operating Temperature Range	−25°C to +85°C
Storage Temperature Range	−65°C to +150°C
Lead Temperature, Storage	60 sec, +300°C
Thermal Resistance
θJC	35°C/W
θJA	120°C/W

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ESD CAUTION

Rev. E | Page 5 of 16