Advanced relays and resistors ensure high signal integrity in the latest generation of test and measurement equipment
By Jeffrey Katz, Product Manager, and Eric Johnsrud, Product Manager, Panasonic
Read this to find out about:
- The demand which test and measurement equipment imposes on electronic components for low noise, low distortion, and high-frequency operation
- New relays which offer long lifetime in fast-switching measurement applications
- Resistors which maintain very accurate resistance values in all operating conditions
Test and measurement equipment provides the foundation on which every facet of technology is built. Without the validation of specifications and performance provided by test and measurement equipment, modern society could not rely on the semiconductors and radio chips in smartphones, PCs, automobiles, and the plethora of gadgets in homes, offices, and factories.
The key requirements for test equipment are accuracy and precision of measurement. This calls for special classes of components which can maintain much lower noise, lower signal loss and lower distortion than standard components, while supporting high data-transfer rates and, in many cases, high switching frequencies.
These requirements apply across the board to nearly all of the components inside test and measurement equipment, including the passive and interconnect components. Here, we highlight the special offerings in relays, resistors, and connectors from Panasonic which are especially well suited to use in test and measurement equipment.
Solid-state PhotoMOS® relays for high signal integrity and long operating life
Relays provide an isolated switching function in many types of test and measurement equipment, insulating low-voltage measurement signals from high-voltage power systems. An excellent illustration of the importance of relays can be found in the Automated Test Equipment (ATE) used in the fabrication of semiconductor chips.
An ATE unit consists of a tester main unit, which is a kind of measurement mainframe, and a test head, which hosts the device under test (DUT). In semiconductor ATE, the test head will carry a probe card, which provides an interface to the wafer which is being tested.
The measurement circuits in the test head feature four types of relays: function relays, dc measurement relays, a circuit protection relay, and a power supply relay, as shown in Figure 1. The specifications of the function and dc relays have to meet extremely demanding requirements.
Fig. 1: The probe card in ATE contains four types of relay
The function relays require ultra-low on-resistance, to minimize attenuation of the measurement signal. The dc relays, on the other hand, require very low output capacitance to minimize signal leakage when the relay is turned off.
These requirements have prompted Panasonic to develop special types of PhotoMOS solid-state relays which offer these valuable characteristics. The AQY22xR PhotoMOS family of relays is offered in compact SSOP and VSSOP packages, and in low on-resistance and low output capacitance types. For instance, for low output capacitance in the dc measurement relays, the AQY221N2V features output capacitance of just 1.0 pF, alongside on-resistance of 9.5 Ω.
By contrast, among the low on-resistance types is the AQV252G, which has on-resistance of just 80 mΩ, as well as output capacitance of 240 pF.
In probe cards and many other types of measurement device, manufacturers are looking to replace traditional electromagnetically actuated reed relays with solid-state relays. This is to benefit from the unlimited operating lifetime of a solid-state relay: a reed relay is typically only rated for around 100 million contact operations. The solid-state relay also provides more flexible mounting options, and very high contact reliability.
Reed relays have retained some support among designers of test and measurement equipment because of one important characteristic: almost zero leakage current, which enables operation at very high switching frequencies. Solid-state relays have an inherently higher level of leakage current than reed relays – a feature of the relay’s internal MOSFET power switch.
For high-frequency circuits based on solid-state relays, Panasonic recommends the use of two low on-resistance relays (S1 and S2) and one low output capacitance relay (S3) in a T-type circuit, shown in Figure 2. In this circuit, any leakage signal is passed to Ground when the main circuit is off, enabling it to maintain high-frequency operation.
Fig. 2: The T-type circuit passes leakage current to Ground
Densely populated probe cards
In an ATE’s probe card, a further requirement is for densely populated board layouts, a card for testing a wafer in a semiconductor fabrication plant can contain hundreds of relays. The small size of PhotoMOS relays is therefore an important advantage. Particularly attractive is the capacitive coupled (CC) type of PhotoMOS relay, in contrast to the standard optically coupled type.
Housed in a TSON package, the AQY2CxRxP CC relays measure just 1.95 mm x 1.80 mm x 0.80 mm. These capacitive coupled relays also feature an extremely low typical operating current of 0.09 mA, and offer guaranteed operation at an ambient temperature of up to 105°C. Like the optically coupled PhotoMOS relays, the CC types are available in low on-resistance and low output capacitance types.
Space saving is also a strong suit of certain capacitors from Panasonic: the EEU-FS aluminum electrolytic capacitors are a radial leaded type which offer a high ratio of capacitance to volume, making them ideal for densely populated test cards. These products also offer long life and high endurance.
Stable, accurate signal measurement
The demand for high accuracy in test and measurement equipment applies to many types of components, and not only to relays. This is reflected in Panasonic’s development of families of resistors which feature extremely accurate and stable resistance values.
In measurement applications, the amplification factor is determined by the resistance value in the circuit around the operational amplifier, as shown in Figure 3. Very accurately maintained resistance values are required to set the amplification factor properly.
Fig. 3: A typical amplifier circuit. The amplification circuit is determined by the values of R1 and R2.
The resistors with the most accurate resistance specifications are the thin-film types. The latest from Panasonic is the ERA-V series, an improved version of the ERA-A series: the ERA-V offers even better stability and reliability. The ERA-V resistance value offers accuracy up to ±0.05%. The temperature coefficient of resistance (TCR) is also excellent, going as low as 10 ppm/K. This compares to the values of a general-purpose high-precision thick-film resistor, and the ERJ6RBD series has tolerance of ±0.5%, and TCR of ±50 ppm/K.
Beyond the accuracy and stability, the ERA-V’s improved construction also offers highly robust and reliable operation:
- A new, smoother substrate provides for better tolerance of ESD strikes
- A bottom stress absorber gives greater tolerance of thermal shock
- An enhanced protective coating and plating offer higher resistance to sulfur corrosion
A second option for more cost-sensitive measurement applications is a high-accuracy family of thick-film resistors. The ERJPB family offers accuracy of ±0.10%, and temperature stability of ±50 ppm/K.
Components to handle high frequencies and data rates
In test and measurement equipment for use in the development or production of RF devices, components need to support high data-transfer rates and high frequencies. In these types of equipment, standard connectors have various deficiencies which can be obviated by use of Active Optical Connectors (AOC) from Panasonic.
The AOC products are completely integrated units which perform all optoelectronic conversion internally, and which are easily mounted to the board with no requirement for the user to connect optical components, an operation which can easily give rise to malfunctions because of contamination or misalignment.
The architecture of the AOC is shown in Figure 4. The device is compatible with any type of differential signal. Used as a replacement for conventional copper signal connectors, the AOC offers higher bidirectional speed of up to 8 Gbits/s, immunity to any type of electrical noise, and excellent electrical insulation. Because of the inherent noise immunity, there is no need to shield the optical fiber cabling, providing valuable space and weight savings compared to copper cabling. The product is supplied as standard with a cable which is up to 1 m long, but custom versions can be supplied which can support cable lengths up to 300 m.
Fig. 4: The AOC is a complete sealed unit which performs optoelectronic conversion internally
As well as offering a noise-immune alternative to copper connectors, the AOC unit is also a superior alternative to standard small form-factor pluggable (SFP) transceivers. SFP transceivers are bulky, typically consume 2 W at a data rate of 10 Gbits/s, and need regular cleaning. The AOC, by contrast, saves as much as 80% of the board space occupied by an SFP transceiver. Because the optical elements are encapsulated within the plug and cable, it requires no cleaning or special preparation each time that a connection is made. And power consumption is considerably lower: just 230 mW at 6 Gbits/s.
In RF testers, another Panasonic connector product offers valuable benefits: the RF35 board-to-FPC connector is fully shielded, and carries RF signals at frequencies up to 15 GHz with very high signal integrity. The RF35 is small, and withstands severe shock and vibration.
Quality and repeatability of high-performance characteristics
Development and production engineers rely on test and measurement equipment to provide accurate and repeatable results, and this means that the characteristics of the components inside the equipment also need to be extremely repeatable and stable.
Thanks to the proven quality of Panasonic’s production processes, the superior characteristics of product series such as the ERA-A resistors and AQY2CxRxP relays can be depended on, to ensure that these Panasonic components enable the equipment manufacturer to maintain the highest standards of signal integrity.