RF Frequency & Power Measurement

The ADL6010 is a versatile, broadband envelope detector covering the microwave spectrum. It provides state-of-the-art accuracy with very low power consumption (8 mW) in a simple, easy to use 6-lead format. The output is a baseband voltage proportional to the instantaneous amplitude of the radio frequency (RF) input signal. It exhibits minimal slope variation of the RF input to envelope output transfer function from 0.5 GHz to 43.5 GHz.

The detector cell uses a proprietary eight Schottky diode array followed by a novel linearizer circuit that creates a linear voltmeter with an overall scaling factor (or transfer gain) of nominally ×2.2 relative to the voltage amplitude of the input.

Although the ADL6010 is not inherently a power responding device, it remains convenient to specify the input in this way. Thus, the permissible input power, relative to a 50 Ω source input impedance, ranges from −30 dBm to +15 dBm. The corresponding input voltage amplitudes of 11.2 mV to 1.8 V generate quasi-dc outputs from about 25 mV to 4 V above common (COMM).

A subtle aspect of the balanced detector topology is that no even-order distortion, caused by nonlinear source loading, occurs at the input. This is an important benefit in applications where a low ratio coupler is used to extract a signal sample and is a significant improvement over traditional diode detectors.

The power equivalent of a fluctuating RF input amplitude can be extracted by the addition of an rms-to-dc converter IC. Alternatively, the baseband output can be applied to a suitably fast analog-to-digital converter (ADC) and the rms value (and other signal metrics, such as peak to average ratio) calculated in the digital domain.

The output response accuracy is insensitive to variation in the supply voltage, which can range from 4.75 V to 5.25 V. The ultralow power dissipation contributes to its long-term stability.

The ADL6010ACPZN is specified for operation from −40°C to +85°C, and the ADL6010SCPZN is specified for operation from −55°C to +125°C. Both are available in a 6-lead, 2 mm × 2 mm LFCSP package.

Applications

• Microwave point to point links
• Microwave instrumentation
• Radar-based measurement systems

The ADL5902 is a true rms responding power detector that has a 65 dB measurement range when driven with a single-ended 50 Ω source. This feature makes the ADL5902 frequency versatile by eliminating the need for a balun or any other form of external input tuning for operation up to 9 GHz.

The HMC802ALP3E is a broadband bidirectional 1-bit GaAs IC digital attenuator in a low cost leadless sur - face mount package. This single positive control line digital attenuator utilizes off chip AC ground capac - itors for near DC operation, making it suitable for a wide variety of RF and IF applications. Covering DC to 10 GHz, the insertion loss is less than 3 dB typical and attenuation accuracy is excellent at ±0.6 dB typ - ical. The attenuator also features a high IIP3 of +55 dBm. One TTL/CMOS control input is used to select the attenuation state and a single Vdd bias of +5V is required.

Applications

The HMC629ALP4E is a broadband 4-bit GaAs IC Digital Attenuator in a low cost leadless SMT package. This versatile digital attenuator incorporates off-chip AC ground capacitors for near DC operation, making it suitable for a wide variety of RF and IF applications. The dual mode control interface is CMOS/TTL compatible, and accepts either a three wire serial input or a 4-bit parallel word. The HMC629ALP4E is housed in a RoHS compliant 4x4 mm QFN leadless package, and requires no external matching components.

Applications

• Cellular/3G infrastructure
• WiBro / WiMAX / 4G
• Microwave radio & VSAT
• Test equipment and sensors 
• IF & RF applications

The ADuCM3027/ADuCM3029 microcontroller units (MCUs) are ultra low power microcontroller systems with integrated power management for processing, control, and connectivity. The MCU system is based on the ARM^® Cortex^®-M3 processor, a collection of digital peripherals, embedded SRAM and flash memory, and an analog subsystem which provides clocking, reset, and power management capability in addition to an analog-to-digital converter (ADC) subsystem. For a feature comparison across the ADuCM3027/ADuCM3029 product offerings, see Table 1.

System features that are common across the ADuCM3027/ADuCM3029/ADuCM3029-1/ADuCM3029-2 MCUs include the following:

• Up to 26 MHz ARM Cortex-M3 processor
• Up to 256 kB of embedded flash memory with error correction code (ECC)
• Optional 4 kB cache for lower active power
• 64 kB system SRAM with parity
• Power management unit (PMU)
• Multilayer advanced microcontroller bus architecture (AMBA) bus matrix
• Central direct memory access (DMA) controller
• Beeper interface
• Serial port (SPORT), serial peripheral interface (SPI), inter-integrated circuit (I²C), and universal asynchronous receiver/transmitter (UART) peripheral interfaces
• Cryptographic hardware support with advanced encryption standard (AES) and secure hash algorithm (SHA)-256
• Real-time clock (RTC)
• General-purpose and watchdog timers
• Programmable general-purpose input/output (GPIO) pins
• Hardware cyclic redundancy check (CRC) calculator with programmable generator polynomial
• Power-on reset (POR) and power supply monitor (PSM)
• 12-bit successive approximation register (SAR) ADC
• True random number generator (TRNG)

To support low dynamic and hibernate power management, the ADuCM3027/ADuCM3029 MCUs provide a collection of power modes and features, such as dynamic and software controlled clock gating and power gating.

The ADuCM3029-1 and ADuCM3029-2 MCU models share the same features and functionality as that of the ADuCM3029 MCU. All specifications pertaining to the ADuCM3027 and ADuCM3029 are also applicable to the ADuCM3029-1 and ADuCM3029-2.

For full details on the ADuCM3027/ADuCM3029 MCUs, refer to the ADuCM302x Ultra Low Power ARM Cortex-M3 MCU with Integrated Power Management Hardware Reference Manual.

Product Highlights

1. Industry leading ultralow power consumption.
2. Robust operation, including full voltage monitoring in deep sleep modes, ECC support on flash, and parity error detection on SRAM memory.
3. Leading edge security. Fast encryption provides read protection to customer algorithms. Write protection prevents device reprogramming by unauthorized code.
4. Failure detection of 32 kHz LFXTAL via interrupt.
5. SensorStrobe^™ for precise time synchronized sampling of external sensors. Works in hibernate mode, resulting in drastic current reduction in system solutions. Current consumption reduces by 10 times when using, for example, the ADXL363 accelerometer. Software intervention is not required after setup. No pulse drift due to software execution.

Applications

• Internet of Things (IoT)
• Electronic shelf label (ESL) and signage
• Smart infrastructure
• Smart lock
• Asset tracking
• Smart machine, smart metering, smart building, smart city, and smart agriculture
• Wearables
• Fitness and clinical
• Machine learning and neural network 

This circuit measures RF power at any frequency from 1 MHz to 8 GHz over a range of approximately 60 dB. The measurement result is provided as a digital code at the output of a 12-bit ADC with serial interface and integrated reference. The output of the RF detector has a glueless interface to the ADC and uses most of the ADC’s input range without further adjustment. A simple two-point system calibration is performed in the digital domain.

The AD8318 maintains accurate log conformance for signals of 1 MHz to 6 GHz and provides useful operation to 8 GHz. The device provides a typical output voltage temperature stability of ±0.5 dB.

The AD7887 ADC can be configured for either dual or single channel operation via the on-chip control register. There is a default single-channel mode that allows the AD7887 to be operated as a read-only ADC, thereby simplifying the control logic.

Typical data is shown for the two devices operating over a −40°C to +85°C temperature range.

This circuit uses the ADL5902 TruPwr^™ detector to measure the rms signal strength of RF signals with varying crest factors (peak-to-average ratio) over a dynamic range of approximately 65 dB and operates at frequencies from 50 MHz up to 9 GHz.

The measurement result is provided as serial data at the output of a 12-bit ADC (AD7466). A simple 4-point system calibration at ambient temperature is performed in the digital domain.

The interface between the RF detector and the ADC is straightforward, consisting of two signal scaling resistors and no active components. In addition, the ADL5902 internal 2.3 V reference voltage provides the supply and reference voltage for the micropower ADC. The AD7466 has no pipeline delay and is operated as a read-only SAR ADC.

The overall circuit achieves temperature stability of approximately ±0.5 dB.

Data is shown for the two devices operating over a −40°C to +85°C temperature range.

The circuit shown in Figure 1 measures peak and rms power at any RF frequency from 450 MHz to 6 GHz over a range of approximately 45 dB. The measurement results are converted to differential signals in order to eliminate noise and are provided as digital codes at the output of a 12-bit SAR ADC with serial interface and integrated reference. A simple twopoint calibration is performed in the digital domain.

The ADL5502 is a mean-responding (true rms) power detector in combination with an envelope detector to accurately determine the crest factor (CF) of a modulated signal. It can be used in high frequency receiver and transmitter signal chains from 450 MHz to 6 GHz with envelope bandwidths over 10 MHz. The peak-hold function allows the capture of short peaks in the envelope with lower sampling rate ADCs. Total current consumption is only 3 mA @ 3 V.

The ADA4891-4 is a high speed, quad, CMOS amplifier that offers high performance at a low cost. Current consumption is only 4.4 mA/amplifier at 3 V. The amplifier features true singlesupply capability, with an input voltage range that extends 300 mV below the negative rail. The rail-to-rail output stage enables the output to swing to within 50 mV of each rail, ensuring maximum dynamic range. Low distortion and fast settling time makes it ideal for this application.

The AD7266 is a dual, 12-bit, high speed, low power, successive approximation ADC that operates from a single 2.7 V to 5.25 V power supply and features sampling rates up to 2 MSPS. The device contains two ADCs, each preceded by a 3-channel multiplexer, and a low noise, wide bandwidth track-and-hold amplifier that can handle input frequencies in excess of 30 MHz. Current consumption is only 3 mA at 3 V. It also contains an internal 2.5 V reference.

The circuit operates on a single +3.3 V supply from the ADP121, a low quiescent current, low dropout, linear regulator that operates from 2.3 V to 5.5 V and provides up to 150 mA of output current. The low 135 mV dropout voltage at 150 mA load improves efficiency and allows operation over a wide input voltage range. The low 30 μA of quiescent current at full load makes the ADP121 ideal for battery-operated portable equipment.

The ADP121 is available in output voltages ranging from 1.2 V to 3.3 V. The parts are optimized for stable operation with small 1 μF ceramic output capacitors. The ADP121 delivers good transient performance with minimal board area. Short-circuit protection and thermal overload protection circuits prevent damage in adverse conditions. The ADP121 is available in tiny 5-lead TSOT and 4-ball, 0.4 mm pitch halidefree WLCSP packages and utilizes the smallest footprint solution to meet a variety of portable applications.

The circuit in Figure 1 is a true rms responding power detector using a variable gain amplifier (VGA) and an rms-responding power detector to provide an extremely wide detection range of approximately 95 dB. RMS detectors are useful in many applications such as receivers and transmitters where accurate measurement of signal power is required. Because the circuit measures rms power, it is suitable for use in systems with diverse or varying crest factors. Examples of such systems include GSM/EDGE, CDMA, WCDMA, TD-SCDMA and LTE based wireless base stations along with any system that uses QAM modulation.

The detection range of the ADL5902 rms detector is 65 dB and is extended to 95 dB by the addition of the linear-in-dB AD8368 VGA. The ADL5902 TADJ function is used to provide temperature stability for the complete circuit. A SAW filter is placed between the VGA to reduce noise and increase sensitivity. This also reduces the frequency range of the circuit to the pass-band range of the SAW filter.

This circuit is a frequency selective, radio frequency (RF) detector that offers 90 dB of detection range from 35 MHz to 4.4 GHz. Unlike a standalone detector that does not discriminate between signals in the frequency spectrum, this circuit has the ability to focus on a narrow band of frequencies, providing enhanced performance over the specified range. The detector circuit is rms responding and stable vs. temperature and frequency, making it an attractive solution for applications that require precise frequency, selective RF power measurement. The circuit also demonstrates strong immunity to unwanted blockers. Figure 1 shows a simplified schematic of the circuit.

The circuit shown in Figure 1 is an accurate 40 GHz, microwave power meter with a 45 dB range that requires only two components. The RF detector has an innovative detector cell using Schottky diodes followed by an analog linearization circuit. A low power, 12-bit, 1 MSPS analog-to-digital converter (ADC) provides a digital output on a serial peripheral interface (SPI) port.

A simple calibration routine is run before measurement operation, at the particular RF frequency of interest. The user can then operate the system in measurement mode. When in measurement mode, the CN-0366 Evaluation Software displays the calibrated RF input power that is applied at the input of the detector in units of dBm.

The total power dissipation of this circuit is less than 9 mW on a single 5 V supply.

The circuit shown in Figure 1 accurately measures return loss in a wireless transmitter from 1 GHz to 28 GHz without any need for system calibration.

The design is implemented on a single circuit board using a nonreflective RF switch; a microwave RF detector; and a 12-bit, precision analog-to-digital converter (ADC). To evaluate the circuit over the widest possible frequency range, a dual-port directional coupler with SMA connectors was used instead of a narrow-band, surface-mount directional coupler.

The circuit measures return loss of up to 20 dB over an input power range of 25 dB (return losses in excess of 20 dB can be measured over a smaller input power range).

A unique feature of the circuit is that it calculates return loss using a simple ratio of the digitized voltages from the RF detector, thereby eliminating the need for system calibration.

The automatic gain control (AGC) circuit is useful in multiple applications such as amplitude stabilization of a synthesizer, controlling output power in a transmitter, or optimizing dynamic range in a receiver. The circuit shown in Figure 1 uses the ADL6010 detector, along with the HMC985A voltage variable attenuator (VVA) and the HMC635 RF amplifier, to provide automatic gain control over a wide range of input frequencies (20 GHz to 37.5 GHz) and amplitude. Circuit performance, as measured by the AGC figures of merit described in this circuit note, are very good between 20 GHz and 30 GHz. The overall gain of the circuit falls off above 30 GHz. However, improvements can be made over narrow bands by using matching techniques not explored in this circuit note.

The AGC circuit has applications in microwave instrumentation and radar-based measurement systems.

The circuit shown in Figure 1 is an RF power measurement circuit that accurately measures the power from an RF signal source within a frequency range of 9 kHz to 6 GHz, and has a nominal input power range of 45 dBm (−30 dBm to +15 dBm).

This circuit constitutes a complete rms RF power meter in a tiny form factor that can be powered entirely from a 5 V USB power supply. The measurement signal chain consists of an rms responding RF power detector and a 12-bit, precision analog-to-digital converter (ADC). These devices are powered by a CMOS linear regulator which generates 3.3 V from the 5 V USB supply.

A simple calibration routine can be performed at multiple frequencies to compensate for any frequency response variation of the circuit. Calibration data is stored in a lookup table, which is referenced during the RF power measurement.

The AD9689-2600EBZ supports the AD9689-2600, a 14-bit, 2.6GSPS dual analog-to-digital converter (ADC). The device has an on-chip buffer and a sample-and-hold circuit designed for low power, small size, and ease of use. This device is designed support direct RF sampling analog signals of up to 5 GHz. The 3 dB bandwidth of the ADC input is greater than 9 GHz. The AD9689 is optimized for wide input bandwidth, high sampling rate, excellent linearity, and low power in a small package.

This reference design provides all of the support circuitry required to operate the ADC in its various modes and configurations. It is designed to interface directly with the ADS7-V2EBZ data capture card, allowing users to download captured data for analysis. The device control and subsequent data analyses can now be done using the ACE software package.