Let’s consider data converters. In the example in Figure 6, we show direct high IF transmitter launch and high IF receiver sampling used, where the data converters are launching and receiving at the intermediate frequency. The IF needs to be as high as can be reasonably achieved to avoid unwieldly image filtering at RF, driving the IF frequency to 3 GHz and above. Fortunately, leading edge data converters are capable of operating at this frequency. The AD9172 is a high performance, dual, 16-bit DAC that supports sample rates up to 12.6 GSPS. The device features an 8-lane, 15 Gbps JESD204B data input port, a high performance, on-chip DAC clock multiplier, and digital signal processing capabilities supporting broadband and multiband direct to RF signal generation up to 6 GHz. In the receiver we show the AD9208, a dual, 14-bit, 3 GSPS 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 product is designed to support communications applications capable of direct sampling wide bandwidth analog signals of up to 5 GHz.
In both the transmit and receive IF stages we suggest digital gain amplifiers that convert from single to balanced and vice versa to avoid the use of baluns. Here we show the ADL5335 in the transmit chain and the ADL5569 in the receive chain as examples of high performance broadband amplifiers.
For the upconversion and downconversion between IF and millimeter wave, we have recently introduced both a silicon-based broadband upconverter, the ADMV1013, and a downconverter, the ADMV1014. These broadband frequency conversion devices operate from 24.5 GHz to 43.5 GHz. This broad frequency coverage allows the designer to address all of the currently defined 5G millimeter wave spectrum bands (3GPP bands n257, n258, n260, and n261) with a single radio design. Both support an IF interface up to 6 GHz and two frequency conversion modes. As shown in Figure 6, both devices include an on-chip 4× local oscillator (LO) multiplier with LO input ranging from 5.4 GHz to 11.75 GHz. The ADMV1013 supports both direct conversion from baseband I/Q to RF and single sideband upconversion from IF. It provides 14 dB of conversion gain at a high output IP3 of 24 dBm. If implemented in a single sideband conversion, as illustrated in Figure 6, the device provides 25 dB of sideband suppression. The ADMV1014 supports both direct conversion from RF to baseband I/Q and image reject downconversion to IF. It provides a conversion gain of 20 dB with a noise figure of 3.5 dB and an input IP3 of –4 dBm. The sideband suppression in image reject mode is 28 dB.
The final component in the RF chain is the ADRF5020 broadband silicon SPDT switch. The ADRF5020 provides both a low insertion loss of 2 dB and high isolation of 60 dB at 30 GHz.
Finally, let’s discuss the frequency sources. Given that the local oscillator may be a large contributor to the EVM budget, it’s important to use a source with very low phase noise for the millimeter wave LO generation.
The ADF4372 is a wideband microwave synthesizer with an industry-leading integrated PLL and ultralow phase noise VCO with output capable of 62.5 MHz to 16 GHz. It allows for the implementation of fractional-N or integer-N phase-locked loop (PLL) frequency synthesizers when used with an external loop filter and an external reference frequency. VCO phase noise at 8 GHz is an impressive –111 dBc/Hz for 100 kHz offset and –134 dBc/Hz at 1 MHz offset.
The block diagram in Figure 6 is a good starting point for any designer considering a millimeter wave design in the 28 GHz and 39 GHz bands and suitable for use with a variety of beamforming front ends requiring a high performance broadband radio. There are also many components listed in ADI’s RF, Microwave, and Millimeter Wave Products Selection Guide that may be of interest to the designer for other signal chain architectures or for similar high frequency applications.