Hittite Simplifies Block Up Converter (BUC) VSAT/Satcom Designs with New, High Performance Chipsets
By Hittite Microwave
Chipsets provide complete coverage for C-, X-, Ku- and Ka-band applications
Introduction: What is a Block Up Converter?
The Block Up Converter (BUC) is part of the transmit chain of any VSAT terminal (Figure 1). It is often located on the feed horn, but if it is a large BUC, it may be located at the base of the antenna and connected with RF conduits (waveguides). Modern BUCs convert the modem’s L-band transmit signal into higher frequency C-band, X-band, Ku-band or Ka-band signals and then amplify the resulting signal before it is reflected off the satellite antenna towards the satellite. It is also worth noting that older BUCs convert from a 70 MHz intermediate frequency (IF) to Ku-band or C-band.
To perform both its functions, the BUC is composed of two individual components: a mixer/local oscillator (LO) and a power amplifier (Figure 2). The mixer/local oscillator performs the frequency conversion between the L-band and the satellite frequency, such as C-band. The resulting satellite frequency is calculated by adding the L-band frequency to the LO frequency. Most BUCs require an external 10 MHz frequency reference to maintain the correct transmit frequency.
BUCs used in remote locations are often 2W or 4W in the Ku-band and 5W in the C-band. Although BUCs are available with high power amplifiers, it is unlikely that a VSAT installation will require more than 10W, even under the most challenging conditions. The 10 MHz reference frequency is usually sent on the same feedline as the main carrier. Many smaller BUCs also get their DC supply over the feedline, using an internal DC block.
BUCs are generally used in conjunction with Low Noise Block Converters (LNBs). The BUC, being an up-converting device, makes up the “transmit” side of the system, while the LNB is the down-converting device and makes up the “receive” side. An example of a system utilizing both a BUC and an LNB is a VSAT system, used for bi-directional internet access via satellite.
The BUC is a block shaped device assembled with the LNB in association with an orthogonal mode transducer (OMT) to the feed horn that faces the reflector parabolic dish. In this way, the BUC is different from other types of frequency upconverters, which may be rack mounted indoors or not co-located with the dish.
Since the BUC is a fundamental element of every VSAT terminal, it naturally follows that any changing trends in the VSAT terminal market are likely to have a large impact on the design requirements of the BUC itself. In recent years, the VSAT market has experienced a few changes which are challenging contemporary VSAT terminals to implement higher levels of efficiency, higher levels of integration, lower energy consumption, and higher reliability – all of which are to be delivered at lower cost.
Simplified, High Performance Solutions for Next Generation BUCs
In recognition of these recent industry developments, Hittite Microwave has committed itself to developing a series of IC chipsets which cover each of the C-, X-, Ku- and Ka-bands, while dramatically reducing the size, complexity, production cost and power consumption levels of the overall Block Up Converter (BUC) design across each of the operating frequency bands.
The chipsets offer complete, highly integrated up conversion solutions that are designed to address the need for higher bandwidth and faster time-to-market in BUCs. The chipset solutions simplify system manufacturing, deployment and inventory management because the chipsets are now highly integrated, such that fewer individual ICs are required. Hittite’s new chipsets also support high order modulation to deliver a significant improvement in spectrum utilization and capacity.
The functional diagram in Figure 3 is an example of how Hittite’s chipsets can be used to realize a complete C-band BUC covering 5.85 to
7.05 GHz. The chipsets convert the 0.95 to 1.55 GHz IF frequencies to a 5.85 to 7.05 GHz transmit signal at the antenna. At the core of the chipset is the HMC6505LC5 GaAs MMIC I/Q upconverter, which features an integrated VGA and delivers a small signal conversion gain of 15 dB with 22 dBc of sideband rejection. The device also exhibits excellent LO to RF rejection of 14 dBc with output IP3 as high as +35 dBm and is housed in a compact 5 x 5 mm ceramic SMT package. The HMC6505LC5 utilizes an RF amplifier preceded by an I/Q mixer, where the LO is driven by a driver amplifier. The IF1 and IF2 mixer inputs are provided and an external 90° hybrid is needed to select the required sideband.
The 4.9 to 5.5 GHz LO signal can be generated by the HMC833LP6GE wideband PLL with integrated VCO, which covers up to 6 GHz and delivers industry leading phase noise and spurious performance. Following the HMC6505LC5 upconverter is the HMC7357LP5GE power amplifier, which operates between 5.5 and 8.5 GHz and is capable of delivering 2W of output power. The amplifier provides 29 dB of gain and +35 dBm of saturated output power at 34% PAE from a +8V supply. The HMC7357LP5GE amplifier also delivers output IP3 of +41.5 dBm and is available in a compact 5 x 5 mm plastic SMT package. For C-band VSAT applications requiring up to 5W, the HMC7733LP6GE can be substituted. The HMC7733LP6GE power amplifier operates from 5.5 to 8.5 GHz and delivers 28 dB gain, +37 dBm P1dB and +43 dBm output IP3. The amplifier also features an integrated power detector and provides adjustable biasing for performance tuning.
Figure 4 shows how Hittite’s chipsets can be used to realize a complete Ku-band BUC covering 13.75 to 14.5 GHz.
Similar to the HMC6505LC5 I/Q upconverter discussed in the C-band VSAT radio implementation above, the highly integrated HMC924LC5 GaAs MMIC I/Q upconverter forms the cornerstone of the chipset. The HMC924LC5 upconverter is housed in a compact, 32-pin 5 x 5 mm SMT ceramic package, provides a high conversion gain of 15 dB and
-30 dBc of sideband rejection. The HMC924LC5 utilizes a RF amplifier preceded by an I/Q mixer where the LO is driven by a driver amplifier. The device takes the 0.95 to 1.7 GHz (IF1 and IF2) mixer input signals from the Tx IF and an external 90° hybrid is used to select the required sideband. The I/Q mixer topology reduces the need for filtering of the unwanted sideband. The HMC924LC5 upconverter also features an integrated variable gain amplifier (VGA) which may be used to facilitate temperature compensation loops.
The LO signal for the HMC924LC5 upconverter varies between 12.8 and 13.05 GHz and is taken from the HMC807LP6CE microwave PLL + VCO which covers 12.4 to 13.4 GHz. The HMC807LP6CE provides low noise and low spurious, which make it ideal for high QAM Block Up Converter applications.
In this example, the output of the HMC924LC5 I/Q upconverter may be driven by either the HMC965LP5E or the HMC995LP5GE, which represent some of Hittite’s best-in-class, high linearity microwave power amplifiers. The HMC965LP5E is a 2W power amplifier which covers the 12.5 to 15.5 GHz frequency band, and delivers +40 dBm output IP3, 27 dB of gain and
+34 dBm saturated output power at 20% PAE. The power amplifier also features an integrated, temperature-compensated power detector which may be used in a closed loop circuit to maintain constant output power over temperature variations. The HMC995LP5GE is a 12-16 GHz 3W power amplifier which also features an integrated on-chip power detector and delivers 27 dB of gain, +35.5 dBm of saturated output power, and 24% PAE from a +7 V supply.
Figure 5 shows the implementation of a complete Ka-band BUC covering 28 to 31.5 GHz. In this example, the HMC798LC4 24-34 GHz Sub-harmonically Pumped (x2) MMIC mixer is being used to upconvert the 0.95 to
1.45 GHz Tx IF signals to the 29.5 to 30 GHz transmit signal. The HMC798LC4 mixer features an integrated LO amplifier, and is available in a leadless RoHS compliant SMT package. The 2LO to RF isolation is excellent at 30 dB, eliminating the need for additional filtering. The LO amplifier is a single bias +5V design with a nominal +4 dBm drive requirement. The RF and LO ports are DC blocked and matched to 50 Ohms for ease of use while the IF covers DC to 4 GHz.
The LO signal is provided by the HMC704LP4E DC to 8 GHz ultra-low phase noise synthesizer, which is used in conjunction with the fully integrated HMC632LP5E voltage controlled oscillator which covers 14.25 to 15.65 GHz.
After some band pass filtering, the HMC6187LP4E analog variable gain amplifier (VGA) is used to set the output power level of the transmit chain. The HMC6187LP4E is rated from 27 to 31.5 GHz and provides up to 13 dB of continuously variable gain control. The VGA also delivers up to 19 dB of gain, +24 dBm output P1dB and up to +31 dBm of output IP3 at maximum gain.
Following the VGA, two HMC7441 2W power amplifiers are shown in a power combining configuration, such that they deliver a total of 4W of transmit power. The HMC7441 amplifiers operate from 27.5 to 31 GHz, provide 23 dB of gain and +34 dBm of saturated output power at 25% PAE from a +6V supply.
Broad Component Offering Covers C-, X-, Ka- and Ku- Frequency Bands
Designers can select from part numbers shown in Table 1, which represent a selection of the components available from Hittite Microwave for VSAT and Satcom applications. These components support the standard C-, X-, Ku- and Ka-VSAT frequency bands. No other supplier offers a broader array of chipset solutions for the VSAT/Satcom market.
Hittite Microwave continues to provide a broad array of innovative, high performance VSAT/Satcom chipset solutions to cover the C-, X-, Ku- and Ka- frequency bands.
All of the chipsets featured are compact, high performance, highly integrated, low power solutions that are positioned to meet the needs of BUC designers. New generations of power amplifiers, frequency converters and variable gain amplifiers are in development, and will provide further improvements to support the needs of the next generation block up converters and VSAT terminals.
Designers should consult Hittite Microwave directly to discuss specific custom or module VSAT/Satcom application requirements. For more information regarding our roadmap products, please contact
MW@hittite.com. All released data sheets are available at our website.
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