The attribute that makes a signal generator for RF, LTE, and/or 4G wireless design a trusted partner on the testbench is not so much its bandwidth as its accuracy. When you deploy your signal generator as a signal source, you want to use that signal to stimulate a device under test (DUT) and measure specific performance parameters of that device. What you do not want to measure is the signal generator.
In the meantime, RF design challenges continue to stiffen. We want to see data rates of at least 1 Gbit/s from a wireless local-area network (WLAN) whether we’re sitting in Starbucks or on the freeway doing 70 mph. Receivers, particularly for surveillance and radar applications, need to be able to pull small signals out of the noise. And for spectrum management applications, Long-Term Evolution Advanced (LTE-A) and its carrier aggregation mean a greater chance that carriers will add at times, which means having to ensure that the power amplifier can handle large spikes.
Agilent’s answer to these challenges comes in the form of four X-Series signal generators that deliver world-class performance in phase noise, output power, adjacent-channel power ratio (ACPR), error vector magnitude (EVM), and bandwidth (see the figure). The MXG and EXG 6-GHz generators are available in analog and vector versions and offer up to 160 MHz of bandwidth with <±0.2-dB flatness (–120 dB for the EXG models). Agilent characterizes the generators’ front ends over the instruments’ entire range and can flatten the frequency response at any frequency to be near perfect. An internal baseband processing accelerator enables real-time phase and amplitude corrections.
To address radar design applications for aerospace/defense, the X-Series generators use a triple-loop synthesizer to deliver phase-noise performance of –146 dBc/Hz at 1 GHz and 20-kHz offset. The X-Series generators’ low phase-noise performance aids in surveillance applications, which are often situated in urban environments where targets are smaller and slower moving. Doppler radar’s frequency shift is low, so the system is dominated by local-oscillator phase noise. The X-Series’ phase-noise performance helps unmask signals that would otherwise be swamped by system noise.
Agilent’s factory-calibrated channel corrections hold EVM to <0.4% at 15 dBm with or without equalization on the DUT’s receiver. The instruments’ ASIC performs amplitude and phase corrections simultaneously, and this translates directly into EVM performance. Engineers can push the power amplifier to its limits and will still only be measuring the amplifier and not the generator.
For spectrum interference applications, the generators’ adjacent-channel power ratio of up to –69 dBc for LTE and up to –73 dBc for W-CDMA is a boon to designers trying to repurpose an existing transmit chain for LTE. That transmit chain may be dealing with GSM, W-CDMA, and LTE all at the same time.
All of these modulation types push a power amplifier to deliver more power, which in turn creates risks of nonlinear operation and distortion. Distortion manifests itself as adjacent-channel harmonic distortion. With their outstanding ACPR performance, the X-Series generators can drive a power amp into compression and measure those nonlinearities without additional noise from the instrument itself.
A deep playback memory allows use of non-standards-based signal environments. Users can stream from memory at the full 160-MHz bandwidth for five seconds at 200 Msamples/s.
The two models in the EXG line are optimized for manufacturing applications. These are the EXG N5171B analog signal generator (starts at $6900) and the EXG N5172B vector signal generator (from $16,970). For R&D applications, the MXGN5181B is the analog version (from $15,500), while the MXG N5182B is the vector model (from $19,320). The EXG models offer a bit less phase-noise performance at –121 dBc/Hz at 1 GHz and a vector bandwidth of 120 MHz.