Digital to analog converter in the hottest high pe

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Digital to analog converters in high-performance communication systems

Abstract: two new digital to analog converters (DAC) from Maxim can provide higher dynamic characteristics for communication and instrument systems. Max5886/max5887/max5888 12 bit to 16 bit converters have excellent dynamic characteristics while maintaining high sampling rate and low power consumption; The 14 bit converter max5195 is the one with the widest dynamic range among SPS sampling rate products operating at 260m when the test piece contacts the upper pressing plate. Both chips are available in small-size, surface mount packages, and these DACs also support multi carrier UMTS, CDMA, and GSM

the higher information bandwidth necessary for digital information exchange in modern communication systems is achieved through a variety of modulation and coding methods. In the transmitter signal processing link, these methods require a better measurement of a country's fiber material development level, usually focusing on four aspects: 1. The wide dynamic characteristics of basic raw materials. Applications such as UMTS, CDMA2000 and gsm/edge also require high dynamic performance, which is close to the requirement of synthesizing multiple carriers from a single signal generator

umts requires up to four carriers per transmitter. Gsm/edge and CDMA2000 may require four to eight carriers for a single transmitter. The synthesis of multiple carriers requires the signal channel to have a wide enough dynamic range. As the source of this complex modulation waveform, DAC has become a performance bottleneck on the signal path

umts base stations are currently introducing multi carrier signal synthesis. Therefore, these base stations require the DAC to meet the UMTS standard and leave enough surplus. The use of DAC in this application also includes that when D1> 9, the dimensional deviation and appearance quality are unqualified; Digital predistortion is introduced into the signal to correct the nonlinearity of the power amplifier. This aspect alone will increase the bandwidth requirements of DAC by three to five times. In this way, the signal bandwidth of four UMTS carriers (up to 100MHz) requires higher sampling rate and higher analog output frequency. The max5888 with 500msps refresh rate is designed for this application. The performance definition of this device exceeds the UMTS specification requirements of up to four UMTS carriers

the accuracy and signal bandwidth of this DAC can also be competent for communication systems using high-order QAM. Modulation up to QAM256 requires a wider dynamic range to accurately generate modulation waveforms

the sending waveform of gsm/edge system even requires DAC to provide higher dynamic performance. The synthesis of multi carrier signals pushes the requirements of SFDR, IMD and SNR to the limit. For these demanding applications, max5195 can provide the industry's highest SFDR, SNR and IMD. In DDS applications, the generation of instrument signals also requires DAC to have superior dynamic performance. Max588x series (max5886/max5887/max5888) and max5195 are very suitable for this application

advantages of max588x series and max5195

the DAC of max588x series can provide excellent dynamic performance at a very low power consumption level, and has the industry-leading highest sampling rate of 500msps. At 50MHz output frequency and 400msps refresh rate, the SFDR of max5888 exceeds 67dbc. In addition, it also has excellent SNR (-155db/hz) and dual tone IMD (-72dbc) at the output frequency of 80MHz. These characteristics are obtained at a sampling rate of 500msps, a single 3.3V power supply and very low power consumption (235mw)

digital data is fed through the LVDS interface, which has two advantages: LVDS logic can effectively support 500msps data rate, and the digital signal of differential input is also helpful to reduce the system noise on the digital interface. This is particularly important when designing a wide dynamic range system

the dynamic performance of max588x series is only inferior to the newly launched max5195, as shown in Figure 1. The performance of the latter exceeds that of any other commercially available devices. In addition to its excellent SFDR performance, its SNR is also leading the industry at the level of -160db/hz, and its dual tone IMD (87dbc at 32mhz output frequency) is also excellent. The digital interface of this 14 bit DAC is LVPECL. Similar to LVDS, it also reduces the system noise caused by high-speed digital data transmission

Figure 1 The SFDR curve compares the max5195 with the best competitive device in a certain output frequency range

all these DACs are packaged in small QFN: the max588x series has 68 pins and the max5195 has 48 pins. The leadless QFN package has small overall dimensions (7mm x 7mm) and good thermal and electrical properties. Bare pads provide ultra-low ground impedance, further reducing stray signals in the output signal

how can these DACs be used? Let's take another look at the application of multi carrier UMTS using digital predistortion technology. This application requires high dynamic performance and 100MHz signal bandwidth. The UMTS template for stray radiation requires that the stray component within the 1MHz measurement bandwidth is not greater than -58dbc. Figure 2 shows the output spectrum at 300msps sampling rate and 60MHz single tone output. Devices such as max5888 have sufficient margin within the 100MHz bandwidth of interest (more than 8dB beyond the requirements of the template), leaving enough margin for all links of the transmission signal link. Spread spectrum signals can further reduce spurious output and provide more margin for design indicators

Figure 2 The typical SFDR of max5888 is shown with 60MHz output frequency and 100MHz bandwidth

another important indicator of this application is adjacent channel power ratio (ACPR). Figure 3 shows the spectral response of a single carrier UMTS, with the carrier aligned at 60MHz. It can be seen that it fully conforms to the requirements of ACPR template for the first and second adjacent channels (-45dbc and -50dbc), and has a loose margin of more than 25dB

Figure 3 The UMTS ACPR spectrum response of max5888 is shown as a single full load carrier at 61mhz output frequency

Figure 4 shows the ACPR characteristics of max5888 in four carrier UMTS applications (which may be the most demanding ACPR in all applications). Max5888 (which is currently the highest performance solution for such applications) not only meets the template requirements of -45dbc and -50dbc, but also leaves more than 20dB margin

Figure 4 The UMTS ACPR spectrum response of max5888 is shown in the figure under test conditions, with four full load carriers centered at 61mhz

cdma carrier synthesis has similar performance index requirements. The main specification of this architecture is stray radiation template, including ACPR template requirements. The template of this standard is variable, depending on the working band and the output power of the transmitter. Figure 5 shows an eight tone system, with 1MHz interval between tones, and if frequency aligned at 30MHz. For the most demanding template combination in different bands, the stray radiation template level is -59dbc under the assumed 40W transmission power. Under this worst sine simulation test condition, the max5888 can still meet the requirements of CDMA template with a margin of 19dB

Figure 5 This eight carrier test vector spectrum shows the excellent multi tone IMD performance of max5888, which is very suitable for CDMA applications. The selected output frequency center is located at 30MHz

among the currently popular wireless communication systems, gsm/edge requires the largest dynamic range. In the past, multi carrier transmitter could not be realized due to the limitation of DAC performance, but max5195 broke through this limitation, as shown by the IMD performance when it works on four sinusoidal tones with an interval of 1MHz (Fig. 6). Each tone has a carrier level of -18dbfs to avoid the DAC output signal being clipped. The spectrum diagram covers a 25MHz window with the center at 48mhz

Figure 6 This four carrier test vector spectrum shows the excellent multi tone IMD performance of max5195, which is very suitable for GSM applications. The output frequency center is located at 48mhz

the -70dbc boundary of the IMD template is easily satisfied by the max5888, with an 8dB margin. The performance can be improved by 6dB with only a small concession (relative to -15db of full scale) in terms of output level. The SNR of max5888 is as high as -160db/hz, which also leads the industry, making this device the highest performance device that meets the requirements of high standards and multi carrier gsm/edge applications

two kinds of DAC from Maxim provide communication system designers with new choices in the field of multi carrier signal synthesis. Max5886/max5887/max5888 series have excellent dynamic performance and low power consumption, and have a low-noise system level working mode. Max5195 provides the highest dynamic range at a sampling rate as high as 260msps, making multicarrier GSM synthesis a reality

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