AD637JRZ - 0.25% RMS-to-DC Converter, 200kHz | Analog Devices
MPN: AD637JRZ β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $12.26 | $12.26 |
| 10 | $11.65 | $116.50 |
| 100 | $11.04 | $1,104.00 |
| 500 | $10.49 | $5,245.00 |
| 1,000 | $9.97 | $9,970.00 |
AD637JRZ Overview
An RMS-to-DC converter is a specialized analog computing IC that produces a DC output proportional to the root-mean-square (RMS) value of its input signal, regardless of waveform shape. Within the signal chain hierarchy, it sits between the analog front end and the ADC or metering stage, enabling true-RMS measurement of AC signals where simple average-responding circuits fail, such as for noise, distorted, or pulsed waveforms.
Key features of the AD637JRZ include true RMS, mean-square, and absolute-value computation modes, a wide supply range of plus/minus 3V to plus/minus 18V, and a supply current of only 2.2 mA with power dissipation of approximately 108 mW. The device offers accuracy comparable to discrete and modular techniques, which historically cost far more and occupied more board area.
Technically, the AD637 uses an implicit analog computation architecture based on a translinear multiplier-divider cell and an active low-pass filter/averaging stage. The J-grade device specified here guarantees 0.25% of reading accuracy, while the same die family is offered in A, B, and K grades with tighter error limits. The wide 200 kHz bandwidth supports measurement of audio, mains-harmonic, and medium-frequency signals.
Typical applications include true-RMS panel meters and DMM front ends, RF and audio power measurement, industrial process monitoring of distorted waveforms from variable-frequency drives, and noise measurement instrumentation. Its low supply current also suits portable test equipment.
Design consideration: the averaging capacitor on the external filter pin sets ripple and settling trade-offs; larger capacitance reduces output ripple but extends settling time, so choose it based on the lowest measurement frequency.
This page synthesizes distributor pricing, verified drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for AD637JRZ β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
AD637KRZ
β Drop-Inπ Reference alternative (not in catalog)
AD637BRZ
β Drop-Inπ Reference alternative (not in catalog)
AD637ARZ
β Drop-Inπ Reference alternative (not in catalog)
AD637JRZ Maximum Ratings & Electrical Characteristics
| Function | True RMS-to-DC Converter |
| Computation Modes | True RMS, Mean Square, Absolute Value |
| Conversion Accuracy | 0.25% of reading |
| Measurement Bandwidth | 200 kHz |
| Supply Voltage Range | +/-3 V to +/-18 V |
| Supply Current | 2.2 mA |
| Power Dissipation | 108 mW |
| Package | 16-SOIC (SOIC-16, wide body) |
| Mounting Type | Surface Mount |
| Grade | J Grade |
| Product Family | AD637 High Precision, Wideband RMS-to-DC Converter |
| RoHS Status | Compliant (Z suffix = RoHS compliant) |
| Reel Packaging Variant | AD637JRZ-RL (Tape & Reel) |
| Output Type | Analog DC voltage proportional to input RMS |
AD637JRZ 16-soic (soic-16, wide body) Pin Configuration Guide
Pin configuration for AD637JRZ (16-soic (soic-16, wide body) package). This analog component features input, output, and power supply pins. Refer to the manufacturer datasheet for offset null, compensation, and enable pin configurations. Ideal for signal conditioning and amplifier circuits.
No detailed pinout data available for AD637JRZ.
Refer to the datasheet for full pin configuration.
Typical Applications
AD637JRZ is suitable for 6 applications: True-RMS Digital Multimeter Front End, Industrial Motor and VFD Output Monitoring, Audio Power and Noise Measurement, Power Supply Ripple and Noise Testing, Process Control AC Signal Monitoring, Automated Test Equipment (ATE) AC Channels.
True-RMS Digital Multimeter Front End
The AD637JRZ is a natural fit for DMM and panel meter AC measurement front ends because it computes the true RMS of any waveform with 0.25% of reading accuracy, eliminating the sine-wave-only calibration error of average-responding circuits. Placed after the AC attenuator and before the ADC, it converts the measured AC signal to a DC level that a standard integrating ADC can digitize directly. With a 200 kHz bandwidth, it covers audio-frequency and mains-harmonic measurement ranges, and its 2.2 mA supply current keeps battery drain acceptable in handheld instruments running from plus/minus 5V rails. The averaging capacitor choice governs settling on range changes, so meter designers balance ripple against auto-range speed using the datasheet sizing equations.
Recommended
Industrial Motor and VFD Output Monitoring
Variable-frequency drive outputs contain high harmonic content and switching artifacts that make average-responding AC measurement unreliable, often by tens of percent. The AD637JRZ measures the true RMS of these distorted waveforms with 0.25% accuracy, giving control and protection circuits a reading that reflects actual heating and power rather than an averaged approximation. Powered from plus/minus 3V to plus/minus 18V industrial rails with only 108 mW dissipation, it can sit directly on the analog conditioning board after isolation and attenuation. Designers typically low-pass filter the converter output before feeding the plant ADC, and size the averaging capacitor for the lowest fundamental frequency the drive can output, which at very low drive frequencies demands large capacitors and longer settling windows.
Recommended
Audio Power and Noise Measurement
Audio-level meters, loudspeaker protection circuits, and acoustic noise measurement instruments all require waveform-independent level detection, which is exactly what the AD637JRZ provides. Its 200 kHz bandwidth comfortably covers the full audio band plus margin, and the 0.25% accuracy supports calibrated sound-level and audio-power measurements without per-unit trimming. In a typical noise measurement chain, the microphone preamplifier output is bandpass filtered to the weighting curve, then applied to the AD637JRZ whose DC output drives the meter display or logger ADC. The absolute-value mode can also be exploited for average-rectified measurements when legacy meter ballistics must be emulated. Low 2.2 mA current draw suits portable acoustic analyzers powered from dual battery rails.
Recommended
Power Supply Ripple and Noise Testing
Production test stations verifying power supply output ripple benefit from the AD637JRZ because ripple and switching noise are non-sinusoidal, and true-RMS conversion yields the noise power a downstream load actually experiences. AC-couple the supply output through a suitable blocking network into the AD637JRZ, band-limit per the test specification, and read the DC output as the RMS ripple voltage. With a 200 kHz bandwidth, the converter captures switching-frequency artifacts from converters operating in the tens to hundreds of kilohertz range. The 0.25% accuracy supports pass/fail limits without frequent recalibration, and operation from the same plus/minus rails as the test fixture analog section simplifies instrumentation power design. Settling time after input step changes is controlled by the averaging capacitor value.
Recommended
Process Control AC Signal Monitoring
In process industries, AC-coupled sensor signals such as vibration pickups, flow turbine pulses, and conductivity excitation echoes must be converted to stable DC levels for PLC and DCS input modules. The AD637JRZ performs this conversion with 0.25% of reading accuracy regardless of signal shape, so alarm thresholds calibrated once remain valid as process conditions change the waveform character. Its wide plus/minus 3V to plus/minus 18V supply range accommodates standard industrial analog rails, and 2.2 mA consumption simplifies intrinsically-safe and loop-powered budgets. Placing the converter close to the sensor conditioning stage and filtering its output before the plant ADC yields a robust measurement chain resistant to harmonic distortion and noise bursts common on plant floors.
Recommended
Automated Test Equipment (ATE) AC Channels
ATE racks often need hundreds of AC measurement channels where board area and cost per channel dominate. The AD637JRZ replaces discrete multiplier-divider and modular RMS solutions that Analog Devices describes as far larger and more expensive, while maintaining comparable accuracy, bandwidth, and dynamic range in one 16-SOIC device. Each channel can be built as attenuator, AD637JRZ, filter, and ADC input, and the 200 kHz bandwidth covers a wide stimulus repertoire including arbitrary and modulated waveforms. Because the AD637JRZ shares its SOIC-16 footprint with AD637 grade variants A, B, and K, ATE builders can populate higher-accuracy grades only on calibration-critical channels and use A-grade parts elsewhere, all on one PCB layout, reducing both BOM complexity and spare-part inventory.
Recommended
Recommended Products Summary
Engineering reference data for AD637JRZ β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | AD637KRZ | AD637BRZ | AD637ARZ |
|---|---|---|---|---|
| Package | SOIC-16 | SOIC-16 - same | SOIC-16 - same | SOIC-16 - same |
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Accuracy Grade | J (0.25% of reading) | K (tighter than J) | B (tightest) | A (relaxed) |
| Measurement Bandwidth | 200 kHz | 200 kHz | 200 kHz | 200 kHz |
| Supply Voltage Range | +/-3 V to +/-18 V | +/-3 V to +/-18 V | +/-3 V to +/-18 V | +/-3 V to +/-18 V |
| Supply Current | 2.2 mA | 2.2 mA | 2.2 mA | 2.2 mA |
| RoHS / Lead-Free | Compliant (Z suffix) | Compliant (Z suffix) | Compliant (Z suffix) | Compliant (Z suffix) |
| Pin Compatibility | AD637 SOIC-16 pinout | Pin-to-pin identical | Pin-to-pin identical | Pin-to-pin identical |
| Relative Cost | Mid (J grade) | Higher than JRZ | Highest of the grades | Lowest of the grades |
Key Differentiators
- Balanced accuracy/cost in the AD637 grade ladder (vs AD637KRZ)
- Tighter guaranteed accuracy available without redesign (vs AD637ARZ)
- High accuracy at moderate bandwidth vs lower-power RMS converters (vs AD736JRZ-R7)
Design Notes
The averaging capacitor connected to the AD637's external filter pin is the most common design error. Estimated: ripple error scales inversely with C_avg times the input frequency, so a capacitor sized for a 10 kHz input will show significant output ripple at 50/60 Hz mains measurement. Size the capacitor from the datasheet ripple equations for the lowest frequency in your measurement range, and accept the proportional increase in settling time on range changes or input steps.
Keep the input attenuation network close to the AD637JRZ input pin and use a ground guard or short feedback path around the high-impedance summing node to limit leakage and noise pickup. Decouple both supplies with 0.1 uF ceramic capacitors placed within a few millimeters of the pins, plus bulk capacitance per rail. Because the output is a slow DC level, route it away from switching nodes; residual ripple on the output can otherwise alias into the downstream ADC readings.
The 200 kHz bandwidth of the AD637JRZ means input signals above the measurement band still reach the internal squaring circuitry. Band-limit the input with an anti-alias or low-pass filter ahead of the converter when high-frequency out-of-band noise is present, otherwise it contributes to the measured RMS even though it is outside the specified bandwidth. This is especially important in industrial environments with switching noise from nearby drives and converters.
Compliance Information
Z suffix denotes Analog Devices RoHS-compliant, lead-free construction per ADI part numbering and distributor listings. REACH and conflict minerals status not stated in provided data - confirm on analog.com product page.
