The megatrend to achieve seamless voice connectivity has dramatically changed the need for wireless infrastructure networks. As the wireless market evolves globally. These wireless networks therefore operate at different frequencies depending on the degree of country and infrastructure development. Evolving RF and emerging new wireless standards further drive the market's need for fully integrated, adaptive chipsets. The key to meeting the ever-changing needs of the wireless market is that we need to come up with a total solution that meets the OEM's basic need to improve design efficiency while reducing design costs, while further ensuring enhanced voice capabilities and high quality. Voice transmission performance. This article explores Texas Instruments' family of radio frequency transceiver (TRF) analog signal chain solutions with flexible design features and enhanced sound quality. In addition, we will also discuss how OEMs, service providers and even the RF market can benefit from the perspective of the market and consumers.
introductionThe ability to implement seamless voice and data connectivity technologies will impact the design requirements of the wireless infrastructure. System capacity must continue to increase, which requires higher bandwidth signals and multi-carrier capabilities. The higher the power of the transmitter and the sensitivity of the receiver, the wider the signal coverage. To ensure that signals are ubiquitous, the network needs smaller pico bases (TITIs) throughout the city to provide services. To this end, OEMs should be able to provide higher performance devices while ensuring efficient, low cost designs.
In addition, OEM systems must support a variety of existing wireless standards including CDMA2000, WCDMA, GSM, and EDGE, as well as emerging standards such as TD-SCDMA in China and WiMAX for global broadband data services. A flexible architecture should meet most or all types of modulation requirements, which is critical to maximizing design resources and increasing reliability. The diversity of the global operating band further exacerbates the complexity, with most voice communications ranging from 800 MHz to 2.1 GHz and data services ranging from 3.5 GHz to 5.6 GHz.
The diversity of these bands requires a highly flexible solution that can meet the needs of multiple frequency bands and various wireless modulation standards. With this in mind, TI has introduced a highly flexible direct upconversion solution that meets these requirements, and its superior RF performance meets stringent base station specifications. In addition, the solution's high level of integration is ideal for small, compact, low-cost designs.
Transmitter architectureThe two architectural options for the transmitter are the direct upconversion architecture and the superheterodyne architecture. The traditional superheterodyne architecture consists of two mixing stages, the signal is first upconverted to a fixed intermediate frequency (IF) signal and then passed through a narrowband surface acoustic wave (SAW) filter. The direct conversion scheme bypasses the IF stage and converts directly from the baseband signal to the selected RF channel signal. Figure 1 shows the structure of the above two architectures.
Figure 1 Superheterodyne architecture and direct upconversion architecture
The direct upconversion scheme uses quadrature modulators and eliminates the hassle of using additional mixing stages, synthesizers, and SAW filters, which not only greatly simplifies design but also significantly reduces bill of materials (BOM) cost. In addition, the scheme can be used for various modulation technologies including CDMA, GSM, and OFDM, and thus has the highest flexibility.
Since no narrowband filters are required, the architecture supports a variety of signal bandwidths corresponding to the chosen modulation scheme. For example, in addition to supporting various bandwidths associated with CDMA2000 and WCDMA, it also supports a variety of WiMAX signal bandwidths typically ranging from 3.5 MHz to 10 MHz. Multi-carrier applications are also supported due to no bandwidth limitations. In addition, the direct upconversion architecture supports digital predistortion (DPD) linearization signals. The signal must have a bandwidth of up to five times the desired signal bandwidth, which includes third- and fifth-order products that have been modified to eliminate the nonlinear effects of the power amplifier.
Direct up-conversion modulatorThe direct upconversion modulator consists of a differential in-phase (I) and quadrature-phase (Q) signal, which are summed at the output. The direct upconversion method must use a quadrature modulator. Based on the inherent characteristics of the quadrature modulator, the local oscillator (LO)'s own signal and unnecessary image signals (or unwanted sidebands) are naturally suppressed without the need for a filter.
The amount of sideband suppression depends on the amplitude and phase balance of the input quadrature component. The LO leakage depends on the DC offset balance between the two input paths of IQ. It is better for the device itself to have better than 35 dBc rejection of the LO leakage and unwanted sidebands, as the two indicators of the quadrature modulator may deteriorate with temperature. If further suppression is required, we can further fine tune in the digital-to-analog converter (DAC). Data converters such as the TI DAC5687 provide an I/Q interface with built-in regulation to meet amplitude and phase balance requirements and support DC offset correction.
The key parameters of the TI TRF3703 modulator are given in Table 1 below. The linearity and output noise parameters of the modulator are critical to system performance settings. These parameters determine the operating output range of the device and also limit the maximum output power of the entire radio system. For modulated signals with very high peak-to-average ratio (PAR) such as CDMA and OFDM, the modulator should avoid a large negative impact on adjacent channel power ratio (ACPR) performance when transmitting signal peaks, which meets the requirements of the standard. is crucial.
Table 1 TRF3703 RF parameters
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