AD636JD-AD636JH Fast Delivery |IC PHOENIX CO.,LIMITED

AD636JD ,Low Level, True RMS-to-DC ConverterFEATURESFUNCTIONAL BLOCK DIAGRAMTrue RMS-to-DC Conversion200 mV Full ScaleLaser-Trimmed to High Acc ..
AD636JH ,Low Level, True RMS-to-DC ConverterSPECIFICATIONS S SModel AD636J AD636KMin Typ Max Min Typ Max Units ..
AD636JH ,Low Level, True RMS-to-DC ConverterCHARACTERISTICSSignal Range, All SuppliesContinuous rms Level 0 to 200 0 to 200 mV rmsPeak Transien ..
AD637AQ ,High Precision, Wide-Band RMS-to-DC ConverterCHARACTERISTICSSignal Range, – 15 V SupplyContinuous RMS Level 0 to 7 0 to 7 0 to 7 V rmsPeak Trans ..
AD637AR ,High Precision, Wide-Band RMS-to-DC Converterapplications; twoconverter that computes the true rms value of any complexaccuracy grades (A, B) fo ..
AD637BQ ,High Precision, Wide-Band RMS-to-DC ConverterSPECIFICATIONS (@ +258C, and 615 V dc unless otherwise noted)AD637J/A AD637K/B AD637SModel Min Typ ..
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AD636JD-AD636JH
Low Level, True RMS-to-DC Converter
REV.BLow Level,
True RMS-to-DC Converter
PRODUCT DESCRIPTION
The AD636 is a low power monolithic IC which performs true
rms-to-dc conversion on low level signals. It offers performance
which is comparable or superior to that of hybrid and modular
converters costing much more. The AD636 is specified for a
signal range of 0 mV to 200 mV rms. Crest factors up to 6 can
be accommodated with less than 0.5% additional error, allowing
accurate measurement of complex input waveforms.
The low power supply current requirement of the AD636, typi-
cally 800 mA, allows it to be used in battery-powered portable
instruments. A wide range of power supplies can be used, from2.5 V to –16.5 V or a single +5 V to +24 V supply. The input
and output terminals are fully protected; the input signal can
exceed the power supply with no damage to the device (allowing
the presence of input signals in the absence of supply voltage)
and the output buffer amplifier is short-circuit protected.
The AD636 includes an auxiliary dB output. This signal is
derived from an internal circuit point which represents the loga-
rithm of the rms output. The 0 dB reference level is set by an
externally supplied current and can be selected by the user
to correspond to any input level from 0 dBm (774.6 mV) to
–20 dBm (77.46 mV). Frequency response ranges from 1.2 MHz
at a 0 dBm level to over 10 kHz at –50 dBm.
The AD636 is designed for ease of use. The device is factory-
trimmed at the wafer level for input and output offset, positive
and negative waveform symmetry (dc reversal error), and full-
scale accuracy at 200 mV rms. Thus no external trims are re-
quired to achieve full-rated accuracy.
AD636 is available in two accuracy grades; the AD636J total
error of –0.5 mV –0.06% of reading, and the AD636K
FEATURES
True RMS-to-DC Conversion
200 mV Full Scale
Laser-Trimmed to High Accuracy
0.5% Max Error (AD636K)
1.0% Max Error (AD636J)
Wide Response Capability:
Computes RMS of AC and DC Signals
1 MHz –3 dB Bandwidth: V RMS >100 mV
Signal Crest Factor of 6 for 0.5% Error
dB Output with 50 dB Range
Low Power: 800 mA Quiescent Current
Single or Dual Supply Operation
Monolithic Integrated Circuit
Low Cost
Available in Chip Form
PIN CONNECTIONS &
FUNCTIONAL BLOCK DIAGRAM
is accurate within –0.2 mV to –0.3% of reading. Both versions
are specified for the 0°C to +70°C temperature range, and are
offered in either a hermetically sealed 14-pin DIP or a 10-lead
TO-100 metal can. Chips are also available.
PRODUCT HIGHLIGHTSThe AD636 computes the true root-mean-square of a com-
plex ac (or ac plus dc) input signal and gives an equivalent dc
output level. The true rms value of a waveform is a more
useful quantity than the average rectified value since it is a
measure of the power in the signal. The rms value of an
ac-coupled signal is also its standard deviation.The 200 millivolt full-scale range of the AD636 is compatible
with many popular display-oriented analog-to-digital con-
verters. The low power supply current requirement permits
use in battery powered hand-held instruments.The only external component required to perform measure-
ments to the fully specified accuracy is the averaging capaci-
tor. The value of this capacitor can be selected for the desired
trade-off of low frequency accuracy, ripple, and settling time.The on-chip buffer amplifier can be used to buffer either the
input or the output. Used as an input buffer, it provides
accurate performance from standard 10 MW input attenua-
tors. As an output buffer, it can supply up to 5 milliamps of
output current.The AD636 will operate over a wide range of power supply
voltages, including single +5 V to +24 V or split –2.5 V to16.5 V sources. A standard 9 V battery will provide several
hundred hours of continuous operation.
VIN
–VS
CAV
BUF OUT
BUF IN
+VS
COMMON
IOUT
AD636
ABSOLUTE
VALUE
SQUARER
DIVIDER
SQUARER
DIVIDER
ABSOLUTE
VALUE
AD636BUF OUT
CAV
BUF INRL
COMMON
+VS
VIN
–VS
IOUT
10kV
10kV
10kV
10kV
NC = NO CONNECT
AD636–SPECIFICATIONS(@ +258C, and +VS = +3 V, –VS = –5 V, unless otherwise noted)
dB OUTPUT
IOUT TERMINAL
ORDERING GUIDE
AD636
NOTESAccuracy specified for 0 mV to 200 mV rms, dc or 1 kHz sine wave input. Accuracy is degraded at higher rms signal levels.Measured at Pin 8 of DIP (IOUT), with Pin 9 tied to common.Error vs. crest factor is specified as additional error for a 200 mV rms rectangular pulse trim, pulse width = 200 ms.Input voltages are expressed in volts rms.With 10 kW pull down resistor from Pin 6 (BUF OUT) to –VS.With BUF input tied to Common.
Specifications subject to change without notice.
All min and max specifications are guaranteed. Specifications shown in boldface are tested on all production units at final electrical test and are used to calculate outgoing
quality levels.
ABSOLUTE MAXIMUM RATINGS1
SupplyVoltage
Dual Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .–16.5 V
Single Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+24 V
InternalPowerDissipation2 . . . . . . . . . . . . . . . . . . . .500 mW
Maximum Input Voltage . . . . . . . . . . . . . . . . . . . .–12 V Peak
Storage Temperature Range N, R . . . . . . . . .–55°C to +150°C
Operating Temperature Range
AD636J/K . . . . . . . . . . . . . . . . . . . . . . . . . . .0°C to +70°C
Lead Temperature Range (Soldering60sec) . . . . . . . .+300°C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1000 V
NOTESStresses above those listed under Absolute Maximum Ratings may cause perma-
nent 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.10-Lead Header: qJA = 150°C/Watt.
14-Lead Side Brazed Ceramic DIP: qJA = 95°C/Watt.
METALIZATION PHOTOGRAPH
Contact factory for latest dimensions.
Dimensions shown in inches and (mm).

COM
1a*
1b*
–VS
CAV
7 BUF IN
6 BUF OUT
8 IOUT
PAD NUMBERS CORRESPOND TO PIN NUMBERS
FOR THE TO-116 14-PIN CERAMIC DIP PACKAGE.
NOTE
*BOTH PADS SHOWN MUST BE CONNECTED TO VIN.
STANDARD CONNECTION
The AD636 is simple to connect for the majority of high accu-
racy rms measurements, requiring only an external capacitor to
set the averaging time constant. The standard connection is
shown in Figure 1. In this configuration, the AD636 will mea-
sure the rms of the ac and dc level present at the input, but will
show an error for low frequency inputs as a function of the filter
capacitor, CAV, as shown in Figure 5. Thus, if a 4 mF capacitor
is used, the additional average error at 10 Hz will be 0.1%, at
3 Hz it will be 1%. The accuracy at higher frequencies will be
according to specification. If it is desired to reject the dc input, a
capacitor is added in series with the input, as shown in Fig-
ure 3; the capacitor must be nonpolar. If the AD636 is driven
with power supplies with a considerable amount of high frequency
ripple, it is advisable to bypass both supplies to ground with
0.1 mF ceramic discs as near the device as possible. CF is an
optional output ripple filter, as discussed elsewhere in this data
sheet.
AD636
flows into Pin 10 (Pin 2 on the “H” package). Alternately, the
COM pin of some CMOS ADCs provides a suitable artificial
ground for the AD636. AC input coupling requires only capaci-
tor C2 as shown; a dc return is not necessary as it is provided
internally. C2 is selected for the proper low frequency break
point with the input resistance of 6.7 kW; for a cut-off at 10 Hz,
C2 should be 3.3 mF. The signal ranges in this connection are
slightly more restricted than in the dual supply connection. The
load resistor, RL, is necessary to provide current sinking capability.
VIN
VOUT
CAV
NONPOLARIZED
10kV to 1kV
0.1mF
Figure 3.Single Supply Connection
CHOOSING THE AVERAGING TIME CONSTANT
The AD636 will compute the rms of both ac and dc signals. If
the input is a slowly-varying dc voltage, the output of the AD636
will track the input exactly. At higher frequencies, the average
output of the AD636 will approach the rms value of the input
signal. The actual output of the AD636 will differ from the ideal
output by a dc (or average) error and some amount of ripple, as
demonstrated in Figure 4.
TIME
Figure 4.Typical Output Waveform for Sinusoidal Input
The dc error is dependent on the input signal frequency and the
value of CAV. Figure 5 can be used to determine the minimum
value of CAV which will yield a given % dc error above a given
frequency using the standard rms connection.
The ac component of the output signal is the ripple. There are
two ways to reduce the ripple. The first method involves using
a large value of CAV. Since the ripple is inversely proportional
to CAV, a tenfold increase in this capacitance will effect a tenfold
reduction in ripple. When measuring waveforms with high crest
factors, (such as low duty cycle pulse trains), the averaging time
constant should be at least ten times the signal period. For
APPLYING THE AD636
The input and output signal ranges are a function of the supply
voltages as detailed in the specifications. The AD636 can also
be used in an unbuffered voltage output mode by disconnecting
the input to the buffer. The output then appears unbuffered
across the 10 kW resistor. The buffer amplifier can then be used
for other purposes. Further, the AD636 can be used in a current
output mode by disconnecting the 10 kW resistor from the
ground. The output current is available at Pin 8 (Pin 10 on the
“H” package) with a nominal scale of 100 mA per volt rms input,
positive out.
OPTIONAL TRIMS FOR HIGH ACCURACY
If it is desired to improve the accuracy of the AD636, the exter-
nal trims shown in Figure 2 can be added. R4 is used to trim the
offset. The scale factor is trimmed by using R1 as shown. The
insertion of R2 allows R1 to either increase or decrease the scale
factor by –1.5%.
The trimming procedure is as follows:Ground the input signal, VIN, and adjust R4 to give zero
volts output from Pin 6. Alternatively, R4 can be adjusted to
give the correct output with the lowest expected value of VIN.Connect the desired full-scale input level to VIN, either dc or
a calibrated ac signal (1 kHz is the optimum frequency);
then trim R1 to give the correct output from Pin 6, i.e.,
200 mV dc input should give 200 mV dc output. Of course,
a –200 mV peak-to-peak sine wave should give a 141.4 mV
dc output. The remaining errors, as given in the specifica-
tions, are due to the nonlinearity.
VIN
VOUT
+VS
CAV
+VS
–VS
500kV
OFFSET
ADJUST
470kV
Figure 2.Optional External Gain and Output Offset Trims
SINGLE SUPPLY CONNECTION
The applications in Figures 1 and 2 assume the use of dual
power supplies. The AD636 can also be used with only a single
positive supply down to +5 volts, as shown in Figure 3. Figure 3
is optimized for use with a 9 volt battery. The major limitation
of this connection is that only ac signals can be measured since
the input stage must be biased off ground for proper operation.
This biasing is done at Pin 10; thus it is critical that no extrane-
ous signals be coupled into this point. Biasing can be accom-
INPUT FREQUENCY – Hz
0.01100k
REQUIRED C
–
1.01001k10k
FOR 1% SETTLING TIME IN SECONDS
MULTIPLY READING BY 0.115
Figure 5.Error/Settling Time Graph for Use with the
Standard rms Connection
The primary disadvantage in using a large CAV to remove ripple
is that the settling time for a step change in input level is in-
creased proportionately. Figure 5 shows the relationship be-
tween CAV and 1% settling time is 115 milliseconds for each
microfarad of CAV. The settling time is twice as great for de-
creasing signals as for increasing signals (the values in Figure 5
are for decreasing signals). Settling time also increases for low
signal levels, as shown in Figure 6.
rms INPUT LEVEL
1mV1V10mV
SETTLING TIME RELATIVE TOSETTLING TIME @ 200mV rms
100mV
2.5
Figure 6.Settling Time vs. Input Level
A better method for reducing output ripple is the use of a
“post-filter.” Figure 7 shows a suggested circuit. If a single pole
filter is used (C3 removed, RX shorted), and C2 is approxi-
mately 5 times the value of CAV, the ripple is reduced as shown
in Figure 8, and settling time is increased. For example, with
CAV = 1 mF and C2 = 4.7 mF, the ripple for a 60 Hz input is re-
duced from 10% of reading to approximately 0.3% of reading.
The settling time, however, is increased by approximately a
factor of 3. The values of CAV and C2 can therefore be reduced
to permit faster settling times while still providing substantial
ripple reduction.
The two-pole post-filter uses an active filter stage to provide
even greater ripple reduction without substantially increasing
the settling times over a circuit with a one-pole filter. The values
of CAV, C2, and C3 can then be reduced to allow extremely fast
settling times for a constant amount of ripple. Caution should
Vrms OUT
+VSVIN
–VS
CAV
(FOR SINGLE POLE, SHORT Rx,
REMOVE C3)
Figure 7.2 Pole ‘’Post’’ Filter
Figure 8.Performance Features of Various Filter Types
RMS MEASUREMENTS
AD636 PRINCIPLE OF OPERATION
The AD636 embodies an implicit solution of the rms equation
that overcomes the dynamic range as well as other limitations
inherent in a straightforward computation of rms. The actual
computation performed by the AD636 follows the equation:
Figure 9 is a simplified schematic of the AD636; it is subdivided
into four major sections: absolute value circuit (active rectifier),
squarer/divider, current mirror, and buffer amplifier. The input
voltage, VIN, which can be ac or dc, is converted to a unipolar
current I1, by the active rectifier A1, A2. I1 drives one input of
the squarer/divider, which has the transfer function:
The output current, I4, of the squarer/divider drives the current
mirror through a low-pass filter formed by R1 and the externally
connected capacitor, CAV. If the R1, CAV time constant is much
greater than the longest period of the input signal, then I4 is
effectively averaged. The current mirror returns a current I3,
which equals Avg. [I4], back to the squarer/divider to complete
the implicit rms computation. Thus:
AD636
Addition of an external resistor in parallel with RE alters this
voltage divider such that increased negative swing is possible.
Figure 11 shows the value of REXTERNAL for a particular ratio of
VPEAK to –VS for several values of RLOAD. Addition, of REXTERNAL
increases the quiescent current of the buffer amplifier by an
amount equal to REXT/–VS. Nominal buffer quiescent current
with no REXTERNAL is 30 mA at –VS = –5 V.
REXTERNAL – V
0.501M1k
RATIO OF V
PEAK
SUPPLY
10k100k
Figure 11. Ratio of Peak Negative Swing to –VS vs.
R EXTERNAL for Several/Load Resistances
FREQUENCY RESPONSE
The AD636 utilizes a logarithmic circuit in performing the
implicit rms computation. As with any log circuit, bandwidth is
proportional to signal level. The solid lines in the graph below
represent the frequency response of the AD636 at input levels
from 1 millivolt to 1 volt rms. The dashed lines indicate the
upper frequency limits for 1%, 10%, and –3 dB of reading
additional error. For example, note that a 1 volt rms signal will
produce less than 1% of reading additional error up to 220 kHz.
A 10 millivolt signal can be measured with 1% of reading addi-
tional error (100 mV) up to 14 kHz.
Figure 12.AD636 Frequency Response
AC MEASUREMENT ACCURACY AND CREST FACTOR
Crest factor is often overlooked in determining the accuracy of
The current mirror also produces the output current, IOUT,
which equals 2I4. IOUT can be used directly or converted to a
voltage with R2 and buffered by A4 to provide a low impedance
voltage output. The transfer function of the AD636 thus results:
The dB output is derived from the emitter of Q3, since the volt-
age at this point is proportional to –log VIN. Emitter follower,
Q5, buffers and level shifts this voltage, so that the dB output
voltage is zero when the externally supplied emitter current
(IREF) to Q5 approximates I3.
+VS
COM
OUT
BUFOUT
ABSOLUTE VALUE/
VOLTAGE–CURRENT
VIN
–VS
CURRENT MIRROR
Figure 9.Simplified Schematic
THE AD636 BUFFER AMPLIFIER
The buffer amplifier included in the AD636 offers the user
additional application flexibility. It is important to understand
some of the characteristics of this amplifier to obtain optimum
performance. Figure 10 shows a simplified schematic of the buffer.
Since the output of an rms-to-dc converter is always positive, it
is not necessary to use a traditional complementary Class AB
output stage. In the AD636 buffer, a Class A emitter follower is
used instead. In addition to excellent positive output voltage
swing, this configuration allows the output to swing fully down
to ground in single-supply applications without the problems
associated with most IC operational amplifiers.
Figure 10.AD636 Buffer Amplifier Simplified Schematic
When this amplifier is used in dual-supply applications as an
input buffer amplifier driving a load resistance referred to

Partno	Mfg	Dc	Qty	Available	Descript
AD636JD	ADI	N/a	49	avai	Low Level, True RMS-to-DC Converter
AD636JH		N/a	8	avai	Low Level, True RMS-to-DC Converter
AD636JH	AD	N/a	15	avai	Low Level, True RMS-to-DC Converter