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Introduction

The Rejustor from Microbridge Technologies represents a major technological improvement for analog compensation. Rejustor are typically used in circuit trimming applications where high precision and/or temperature stability is required and the exact value of the desired resistance depends on variation in other circuit components – for example, batch-to-batch or unit-to-unit manufacturing variations, or where packaging-induced stresses cause significant changes in electrical output. The Rejustor's resistance can be adjusted within a range of approximately 30% down from the initial value (or more in some cases). The Rejustor is an analog adjustable resistor. These units can be adjusted hundreds of times and always maintain the last adjusted state, even if they are placed in storage for extended periods. After trimming, these passive devices require no power to hold their trimmed value. Adjusting is performed by applying short duration analog voltage pulses to the trim pin(s). Microbridge provides Rejust-it software to facilitate adjusting. Adjusting can be performed in the factory or in the field. Factory adjusting includes trimming during final assembly, trimming during ATE testing, or trimming at probe for wafers and die. This application note provides an introduction to Rejustors including physical characteristics, typical performance and applications. An overview of Rejust-it software is also provided.

 

Rejustor Basics

A Rejustor contains two basic elements – the resistor and adjustment element. The schematic symbol for the basic Rejustor is shown in Figure 1.

 

The resistive element in the Rejustor is a simple passive, bi-directional resistor with behaviour similar to a thin-film resistor. The adjustment elements are only required during adjustment of the device. The advantage of the Rejustor is that it provides reliable, consistent behavior over temperature, a requirement in the automotive industry. The Rejustor has no moving parts, unlike a potentiometer, and cannot be adjusted in the field unless the operator is using factory-approved adjusting equipment. The Rejustor is the only analog resistor than can be adjusted in-circuit with simple, isolated electrical signals.

In some applications it may be desirable that the Rejustor not be adjustable after final assembly. In this case, the adjustment pins need not be made available after wafer probe or ATE, although it is recommended to connect H-GND to analog ground. Denying access to the adjust pins provides a lock-out to prevent accidental re-trimming of the Rejustor.

Like resistors, Rejustor operate across the frequency spectrum from low frequency, such as sensors, to high frequency such as RF circuitry in wireless base stations.

Microbridge manufacturers Low-TCR Rejustors as standard products. These devices offer resistance-only adjustment with stable TCR across the adjustable range. Available in QFN or SOIC packages for PCB mounting, these devices are used to adjust sensors, amplifiers, regulators, optical components and in a variety of other applications. Low TCR Rejustors are available in tape and reel, or in tubes for sample quantities.

Low TCR Rejustors

• Resistance-adjustment trimming
• Resistance-adjustment trimming
• Adjustment range: 30% down from as-manufactured resistance
• Bi-directional adjustment within active range
• Adjustment resolution to 0.01%
• Precision Temperature coefficient as resistor is adjusted
• TCR: 0±100ppm/°K
• Two electrically isolated Rejustors per package
• 4.7K, 10K, 15K and 90K in 1:1 ratios (both Rejustors have equal as-manufactured resistance)
• 10K available in 1:2, 1:5 and 1:9 ratios
• SOIC 8-pin, or 3mm x 3mm QFN 16-pin

 

Advantages Over Other Technologies

Analog Pots (Manual Mechanical Trimpots)

Analog Pots Limitations Cost (0.10$ to several dollars per unit in volume depending on adjustment resolution) Large form factors Limited adjustment accuracy (5-1%) and poor matching Prone to drift under vibration and temperature Require manual adjustment Limited high-frequency range (inevitable inductance)

Microbridge Rejustors vs. Analog Pots Competitive cost for dual Rejustors in volume Small form factors (SO and QFN packages) Superior adjustment accuracy and matching (0.1% or better) Improve precision and reliability under vibrating conditions (<0.01% change with vibration) Temperature compensation possible Eliminate manual or mechanical operation Higher frequencies (~1GHz or higher)

 

Digital Pots (Configurable Resistor Arrays)

Limitations of Digital Pots (Configurable Resistor Arrays) Cost (0.50-3.00$ per unit in volume depending on # of bits of resolution) Adjustment accuracy depends on # of bits of resolution (7bits=~0.8%, 10bits=~0.1%) - discrete adjustment Not passive components Limited resistance values (typically 10Kohm or higher) due to wiper resistance Limited high-frequency range (~1MHz) Dissipates power (needed for normal operation) Requires non-volatile technology to maintain settings (e.g. E2PROM) with potential associated reliability issues

Microbridge Rejustors vs. Digital Pots Competitive cost for dual Rejustors in volume Superior adjustment accuracy (0.1% or better) True passive operation Wide range of resistance values possible (no ‘wiper' resistance) Higher frequencies (~1GHz or higher) Low power (no power required during operation, only 2-5V, 2-5mA during trimming) Rejustors are a non-volatile device Smaller layout footprint versus DPOT when integrated on chip Potential for multi-order temperature compensation

 

Digital Conditioning

Limitations of Sensor/Signal Conditioning Cost (0.50-3.00$ per unit in volume depending on accuracy) Adjustment accuracy depends on # of bits of resolution used - discrete compensation fit Not passive components Complex configuration by users required Dissipates power (needed for normal operation) Requires non-volatile technology to maintain settings (e.g. E2PROM) with potential associated reliability issues

Microbridge Rejustors vs. Sensor/Signal Conditioning Competitive cost for dual Rejustors in volume Offers precision offset and gain adjustment and temperature compensation as part of pre-conditioning solution Potential for multi-order temperature compensation Can compensate for sensor aging and drift at the source Low power (no power required during operation, only 2-5V, 2-5mA during trimming) Rejustors are a non-volatile device Smaller layout footprint when integrated with semiconductor sensor Complementary with and can be added to current sensor/signal conditioning to improve performance and yield

 

Laser Trimming (Thick Film - Hybrid)

Limitations of Laser Trimming (Thick Film - Hybrid) Trimmed in one direction only One time adjustment, typically before final assembly Limited trim adjustment accuracy (1-0.5%) Technology experience required Manually intensive setup Expensive capital investment ($200K/laser) Can only trim one resistor at a time Resistor must be large enough for laser alignment and trim to desired tolerance

Microbridge Rejustors vs. Laser Trimming (Thick Film - Hybrid) Offers adjustability in both directions Multiple adjustments before or after assembly Superior adjustment accuracy (0.1% or better) Networks of resistors and Rejustors possible Temperature compensation possible Possibility of user-initiated adjustment Automated adjustment with standard test equipment, no lasers Can trim multiple devices simultaneously Trim at temperature as part of production test Low TCR material (0±100ppm/oK) Small form factor (die SO and SOT packages) suitable for hybrid assembly

 

Laser Trimming (Thin Film – integrated circuit)

Limitations of Laser Trimming (Thin Film – Integrated Circuit) Trimmed in one direction One time adjustment before packaging May change during final packaging Technology experience required Manually intensive setup of wafers Expensive capital investment ($0.5-1M/laser) Can only trim one resistor at a time Resistor must be large enough for laser alignment and trim to desired tolerance

Microbridge Rejustors vs. Laser Trimming (Thin Film – Integrated Circuit) Offers adjustability in both directions Multiple adjustments before or after packaging Superior adjustment accuracy (0.1% or better) Temperature compensation possible Possibility of user-initiated adjustment Automated adjustment with standard IC test equipment, no lasers Can trim multiple devices simultaneously Different TCR materials possible (+, -, zero) Similar in size to laser trimmable resistor

 

Fusible Passive Resistor Arrays

Limitations of Fusible Passive Resistor Arrays Not used for precision Trim adjustment accuracy depends on # of resistors and fuses - discrete adjustment Generally trim only in one direction One time adjustment High power to ‘blow' fuse Potential reliability issues Potential large unused layout footprint

Microbridge Rejustors vs. Fusible Passive Resistor Arrays Superior adjustment accuracy (0.1% or better) Bi-directional adjustability with chip level voltage and current (2-5V, 2-5mA to adjust) Multiple adjustments before or after packaging Possibility of user-initiated adjustment Small form factor (similar in size to poly or thin film micro-resistor) Temperature compensation possible

 

 

 Featured Products

Part Number		Description	Data Sheet	App. Notes
1110		Standard Power, R1: 7K-10K; R2: 63K-90K, QFN Package
1111		Low Power, R1: 3.3K-4.7K; R2: 16.5K-23.5K
1112		Standard Power, R1: 7K-10K; R2: 7K-10K, QFN Package
1115		Standard Power, R1: 7K-10K; R2: 14K-20K, QFN Package
1117		Standard Power, R1: 7K-10K; R2: 35K-50K, QFN Package
111C		Standard Power, R1: 10.5K-15K; R2: 10.5K-15K, QFN Package
111D		Standard Power, R1: 63K-90K; R2: 63K-90K, QFN Package
111E		Standard Power, R1: 3.3K-4.7K; R2: 3.3K-4.7K, SOIC Package
111F		Standard Power, R1: 7K-10K; R2: 7K-10K, SOIC Package
111H		Standard Power, R1: 7K-10K; R2: 14K-20K, SOIC Package
111J		Standard Power, R1: 7K-10K; R2: 35K-50K, SOIC Package
111L		Standard Power, R1: 7K-10K; R2: 63K-90K, SOIC Package
111N		Standard Power, R1: 10.5K-15K; R2: 10.5K-15K, SOIC Package
111P		Standard Power, R1: 63K-90K; R2: 63K-90K, SOIC Package
111R		Low Power, R1: 3.3K-4.7K; R2: 3.3K-4.7K
111T		Low Power, R1: 3.6K-9K; R2: 6.3K-9K
111U		Low Power, R1: 10.5K-15K; R2: 31.5K-45K
111Y		Low Power, R1: 10.5K-15K; R2: 10.5K-15K
111Z		Low Power, R1: 23K-33K; R2: 23K-33K
1121		Low Power, R1: 3.3K-4.7K; R2: 16.5K-23.5K
1127		Low Power, R1: 6.3K-9K; R2: 31.5K-45K
MBK-408A		Rejustor Calibration Kit
MBK-500		Matchbox

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