Analog Devices has introduced a pair of highly integrated microwave up- and down-converters, the ADMV1013 and ADMV1014. Both devices operate over an extremely wide frequency range from 24 GHz to 44 GHz and provide 50 Ω matching while supporting instantaneous bandwidths greater than 1 GHz. The performance characteristics of the ADMV1013 and ADMV1014 simplify the design and implementation of small 5G millimeter-wave (mmW) platforms including the 28 GHz and 39 GHz frequency bands commonly found in backhaul and fronthaul applications, as well as many other ultra-wideband transmitters and receivers application.

Each upconverter and downconverter chip is highly integrated (see Figure 1), consisting of an IQ mixer and an on-chip quadrature phase shifter, and can be configured in baseband IQ mode (zero IF, IQ frequency supports dc to 6 GHz), or configured in IF mode (real IF, IF frequency supports 800 MHz to 6 GHz). The RF output of the upconverter integrates a driver amplifier with a voltage-controlled attenuator (VVA), and the RF input of the downconverter includes a low noise amplifier (LNA) and a gain amplifier with VVA. The local oscillator (LO) chain for both chips consists of an integrated LO buffer amplifier, a quadruple, and a programmable bandpass filter. Most of the programming and calibration functions are controlled through the SPI interface, which makes the IC easy to configure through software to excellent performance levels.

Figure 1. (a) ADMV1013 upconverter chip block diagram. (b) Block diagram of the ADMV1014 downconverter chip.

ADMV1013 Upconverter Internal View

The ADMV1013 offers two frequency translation modes. One mode is to upconvert directly from baseband I and Q to the RF band. In this I/Q mode, the baseband I and Q differential input signals range from dc to 6 GHz, such as those produced by a pair of high-speed digital-to-analog converters (DACs). The common-mode voltage range of the IQ input signals is 0 V to 2.6 V; therefore, they can meet the interface needs of most DACs. When the common-mode voltage of the selected DAC is within this range, the interface design can be simplified by configuring the registers of the upconverter so that the input common-mode voltage and the common-mode voltage of the DAC output are optimally matched. Another mode is a complex IF input (such as a signal generated by a quadrature digital upconverter device) with single sideband upconversion to the RF band. The ADMV1013 is unique in its ability to digitally correct the dc offset errors of the I and Q mixers in I/Q mode, thereby improving LO leakage at the RF output. After calibration, the LO leakage at the RF output can be as low as -45 dBm at maximum gain. A more difficult challenge that hinders zero-IF radio designs is the phase imbalance of I and Q, resulting in poor sideband rejection. Another challenge with zero IF is that the sidebands are often too close to the microwave carrier, making filters difficult to implement. The ADMV1013 solves this problem by allowing the user to digitally correct the I and Q phase imbalance through register tuning. During normal operation, the upconverter exhibits an uncalibrated 26 dBc sideband rejection. The sideband rejection can be calibrated to about 36 dBc using the on-chip registers. Both calibration features are implemented via SPI without additional circuitry. In I/Q mode, sideband suppression can be further improved by adjusting the phase balance of the baseband I and Q DACs. These performance-enhancing features help minimize external filtering while improving radio performance at microwave frequencies.

Figure 2. Illustration of the ADMV1013 on the evaluation board in a 6 mm × 6 mm surface-mount package.

With the integrated LO buffer, the required drive force for this part is only 0 dBm. Therefore, the device can be directly driven using an integrated voltage-controlled oscillator (VCO) frequency synthesizer such as the ADF4372 or ADF5610, further reducing the external component count. The on-chip quadruple doubles the LO frequency to the desired carrier frequency, then filters out unwanted doubler harmonics by a programmable bandpass filter placed in the mixer quadrature. before the phase generation block. This layout greatly reduces spurious frequencies entering the mixer, while allowing the part to work in conjunction with an external low-cost, low-frequency synthesizer/VCO. The modulated RF output is then amplified by a pair of amplifier stages with a VVA in between. The gain control Module provides the user with a 35 dB adjustment range, with a maximum cascade conversion gain of 23 dB. The ADMV1013 is available in a 40-pin substrate grid array package (see Figure 2). These features combine to provide superior performance, maximum flexibility and ease of use, while minimizing the number of external components required. Therefore, small microwave platforms such as small cell base stations can be realized.

ADMV1014 Downconverter Internal View

The ADMV1014 has some similar components, such as an LO buffer, quadruple, programmable bandpass filter, and quadrature phase shifter in its LO path. However, built as a downconverter device (see block diagram in Figure 1b), the ADMV1014 has an LNA installed in the RF front end, followed by a VVA and an amplifier. The continuous 19 dB gain adjustment range is controlled by the dc voltage applied to the VCTRL pin. Users can choose to use the ADMV1014 in I/Q mode as a direct demodulator from microwave to baseband dc. In this mode, the demodulated I and Q signals are amplified at the respective I and Q differential outputs. Their gain and dc common-mode voltage can be set by registers via SPI, allowing differential signals to be dc-coupled to, for example, a pair of baseband analog-to-digital converters (ADCs). Alternatively, the ADMV1014 can be used as an image-reject downconverter for a single-ended complex IF port. In either mode, I and Q phase and amplitude imbalances can be corrected via SPI, improving image rejection when downconverting to baseband or IF. Overall, the downconverter delivers 5.5 dB total cascaded noise figure and 17 dB maximum conversion gain over the 24 GHz to 42 GHz frequency range. Cascaded NF remains firmly at 6 dB as the operating frequency approaches the baseband edge (up to 44 GHz).

Figure 3. Illustration of the ADMV1014 on the evaluation board in a smaller 5 mm × 5 mm package.

Dramatically improve 5G mmW radio performance

Figure 4 shows the measured performance of the downconverter at 28 GHz using a 5G NR waveform consisting of 4 independent 100 MHz channels, each modulated to 256 QAM at -20 dBm input power. The measured EVM is -40 dB (1% rms), enabling demodulation of higher order modulation schemes required for mmW 5G. With up-converter > 1 GHz bandwidth capacity, and 23 dBm OIP3 for up-converter and 0 dBm IIP3 for down-converter, the combination can support higher-order QAM modulation for higher data throughput. In addition, the device supports other applications such as broadband communication links for satellite and terrestrial receiving stations, secure communication radios, RF test equipment and radar systems. Its outstanding linearity and image rejection performance is impressive, and when combined with the compact solution size, small form factor, high performance microwave link, enables broadband base stations.

Figure 4. Measured EVM performance (percent rms) versus input power at 28 GHz and corresponding 256 QAM constellation.