Analog Devices RF and Microwave

Software-defined radio (SDR) is a radio communication system where components traditionally implemented in hardware (mixers, filters, modulators) are instead implemented in software. This allows a single hardware platform to support multiple radio standards through software configuration. ADI is a leader in SDR technology with wideband transceivers like AD9361 and ADRV9009 that integrate RF, mixed-signal, and digital processing. Key ADI SDR features: 1) Wide frequency coverage (70MHz to 6GHz for AD9361, up to 6GHz for ADRV9009)

2) Adjustable bandwidth (200kHz to 56MHz)

3) Multiple modulation scheme support (QPSK, QAM, OFDM)

4) Integrated frequency synthesis

5) Digital filtering and gain control

6) JESD204B high-speed digital interface to FPGAs. ADI provides complete reference designs including FPGA HDL code, no-OS drivers, and Linux support. SDR applications include cellular base stations, military communications, public safety radios, and satellite ground stations.

Use AD9361 for 1x1 SDR up to 6GHz; use ADRV9009 for 2x2 MIMO with better performance; both include complete FPGA reference designs.

PLL phase noise requirements depend on your application: 1) Communications systems - phase noise causes reciprocal mixing and degrades receiver sensitivity. For GSM base stations, requirement is typically -130dBc/Hz at 1MHz offset

for LTE, -140dBc/Hz

for 5G mmWave, even lower phase noise is needed

2) Radar systems - phase noise limits Doppler resolution. For Doppler radar detecting 1 m/s velocity at 10GHz requires < -100dBc/Hz at 1kHz offset

3) Satellite communications - very stringent requirements, often -145dBc/Hz at 1MHz offset

4) Instrumentation - depends on measurement accuracy requirements. ADI's ADF4351 offers -110dBc/Hz at 1MHz offset (good for general purpose)

ADF5355 offers -138dBc/Hz (excellent for communications)

ADF4159 offers -224dBc/Hz FOM (state-of-the-art for radar). Lower phase noise typically requires: higher reference frequency, lower PLL bandwidth, higher quality VCO, and cleaner reference clock.

GSM: -130dBc/Hz; LTE: -140dBc/Hz; Radar: <-100dBc/Hz at 1kHz; use ADF5355 for best phase noise performance.

RF mixers can be active (transistor-based) or passive (diode-based), each with advantages: Passive mixers (e.g., ADE-1, ADE-25): use diodes for switching

advantages: very high linearity (IIP3 > 20dBm), no DC power consumption, good noise figure (6-8dB), wide bandwidth

disadvantages: conversion loss (6-10dB), require higher LO power (7-17dBm), no isolation between ports. Active mixers (e.g., ADL5350, ADL5801): use transistors for gain

advantages: conversion gain (instead of loss), lower LO power required (0-3dBm), better port isolation, integrated LO buffers

disadvantages: higher noise figure (10-15dB), lower linearity (IIP3 10-20dBm), require DC power. Choose passive mixers for: highest linearity applications, very wide bandwidth, battery-powered LO drivers. Choose active mixers for: systems needing gain, lower LO power availability, better isolation requirements. Many modern receivers use active mixers for convenience, passive mixers for performance.

Use passive mixers for highest linearity; use active mixers for conversion gain and lower LO power requirements.

RF impedance matching is critical for maximum power transfer and minimal reflections. Standard RF impedance is 50Ω (75Ω for video). Matching techniques: 1) L-networks - use one inductor and one capacitor, simple but narrowband

2) Pi and T-networks - three components, wider bandwidth

3) Transmission line transformers - wideband, used for baluns

4) Stub matching - use transmission line sections

5) Smith chart - graphical tool for designing matching networks. Design procedure: 1) Measure or simulate source and load impedance at operating frequency

2) Calculate required matching network using Smith chart or software (ADS, AWR)

3) Choose component values (consider Q factor and bandwidth)

4) Simulate with parasitics

5) Build and verify with VNA. For narrowband applications (< 10% bandwidth), L-networks are simple and effective. For wideband, use multi-section transformers or distributed matching. ADI's RF amplifiers and mixers typically include internal matching to 50Ω, simplifying design.

Use L-networks for narrowband; use Pi/T networks for wider bandwidth; use Smith chart for design; verify with VNA.

1dB compression point (P1dB) and third-order intercept point (IP3) are key linearity specifications: P1dB is the output power level where amplifier gain drops by 1dB from small-signal gain due to compression. It indicates the maximum useful output power. Example: If small-signal gain is 20dB and P1dB is 20dBm, at P1dB output the actual gain is 19dB. IP3 is a theoretical point where third-order intermodulation products would equal the fundamental signal power. It's calculated by extrapolating the linear gain slope and third-order product slope. Higher IP3 means better linearity. Relationship: IP3 is typically 10-15dB higher than P1dB. For receiver applications, high IP3 prevents strong interferers from generating intermodulation products that can mask weak desired signals. For transmitters, high P1dB allows higher output power. ADI's RF amplifiers specify both P1dB and IP3. Example: ADL5601 has P1dB = 20.6dBm, IP3 = 38.5dBm at 900MHz.

P1dB indicates max output power; IP3 indicates linearity; IP3 typically 10-15dB > P1dB; higher values better for both.