VIEWS: 16 PAGES: 4 CATEGORY: Mobile Devices POSTED ON: 5/27/2011
Phone work in the wait state is called standby. Battery standby time is the mobile phone standby mode in continuous use. Can also be interpreted as a cell phone fully charged battery, without a call, do not shut down the standby mode, the battery has been consumed by its own low-battery warning to appear between the time that can be sustained. Standby current consumption is relatively small, has little to do with the network, according to different models, consumption of a few milliamps to tens of mA current range. Standby time depends on battery capacity and the size of mobile phone current consumption. The standby time of the algorithm are: mobile phone battery capacity / standby operating current = standby time.
TECHNICAL REPORTS Low Power Baseband Modem LSI Authors: Masayuki Yamamoto* and Ryosuke Takeuchi* Mitsubishi Electric Corporation has developed a To extend talk time, talk current was reduced by low power baseband modem LSI for W-CDMA mobile means of (1) minimizing the hardware (to fit into one phones. The LSI was installed in D900i, achieving chip) by optimizing the algorithm and the required approx. 170/90 minutes of continuous talk time for memory size for each function; (2) shortening the circuit voice/video phones, and approx. 550/420 hours of operation time by thoroughly applying a clock gating continuous standby time in stationary/moving states technique to each circuit; and (3) decreasing the inter- respectively. The architecture of this LSI is similar to nal power voltage of the LSI (from 1.8V to 1.5V) by that of the baseband modem LSI chipset used for applying optimized semiconductor process. As a result, D2101V, which was optimized for lowering power con- the operating current for baseband modem processing, sumption. To realize this LSI, 0.15 um low leak semi- which previously accounted for 35%-40% (200mA) of conductor process technology was applied to integrate total talk current was reduced by 85%. The standby an AFE (Analog Front End), a CPU, two DSPs and a time was also extended with reduced standby current hardware accelerator on a 10.6mm-square silicon chip. by means of (4) shortening the processing time by Then the chip was packed into a 15mm-square, modifying the software for standby processing in com- 513-ball FBGA, and along with an external memory munication control, which decreased 90% of the oper- package (stacking 32M-bit Flash ROM and 32M-bit ating current that previously accounted for over PSRAM), the LSI enables baseband modem process- 60%(7mA) of the total standby time; (5) reducing the ing for W-CDMA mobile phones. leak current (to half) by partly turning on/off the internal power of the LSI; etc. External memory (32M-bit Flash ROM + 32M-bit PSRAM) DSP-2 Hardware Accelerator CPU AFE DSP-1 Baseband modem LSI and external memory Baseband modem LSI mounted on a mobile phone board - 0.15um low leak semiconductor process - Chip size: 10.6mm x 10.6mm Baseband modem LSI and external memory mounted on a mobile phone board With 0.15 um low leak semiconductor process, an AFE, a CPU, two DSPs, and a hardware accelerator were integrated on a 10.6mm-square silicon chip. Then the chip was packed into a 15mm-square, 513-ball FBGA, and along with an external memory package (stacking 32M-bit Flash ROM and 32M-bit PSRAM), the LSI enables baseband modem processing for W-CDMA mobile phones. * Mobile Terminal Center 2 TECHNICAL REPORTS 1. Foreword the external memory (32M-bit Flash ROM and 32M-bit The third-generation W-CDMA mobile phone sys- PSRAM) as well. tem has been providing commercial services since Each of the two DSPs is a 16-bit DSP microcom- 2001, offering advanced features such as video phone puter (D10V) which controls the RF block, the hardware and high speed packet communications that are more accelerator, and part of the digital signal processing for attractive than the services based on the second gen- communications in cycles of 667 us. eration system. However, for this new system to be- The hardware accelerator is divided into the come widely adopted, the continuous talk time and channel encoder, modulator, demodulator, and decoder standby time had to be extended. as described in (1)-(4) below: This article describes the low power baseband (1) Encoder modem LSI developed as a solution to this need, start- The encoder performs channel encoding and in- ing with an overview of its basic structure and charac- terleaving by executing convolutional/turbo encoding on teristics, followed by details of the low power technol- the transmitted data, and outputs the results to the ogy. modulator as a transmitted bit sequence. (2) Modulator 2. Baseband Modem LSI The modulator performs data mapping and This baseband modem LSI applies 0.15um low spreading on the transmitted bit sequence to generate leak semiconductor process technology to integrate an the chip sequence, and outputs the results to the AFE AFE, a CPU, two DSPs, and a hardware accelerator on as transmitted digital IQ signal within a limited band- a 10.6mm square silicon chip. Figure 1 shows its archi- width of 5MHz. tecture. The internal power supply of this LSI consists (3) Demodulator of one part that is constantly set on (for the CPU, two The searcher performs cell search and path timing DSPs, and AFE) and the other part that can be detection for the received digital IQ signal input from switched on/off for the hardware accelerator. The ar- the AFE. The finger performs RAKE receiving to exe- chitecture of this hardware is similar to that of the cute despreading and pilot coherent detection on each baseband modem LSI chipset(1)(2) used for D2101V. of the detected delay paths, and outputs the obtained General functionality of the LSI is described below. bit sequence to the decoder block. The AFE contains AD/DA converters, transmits (4) Decoder /receives analog IQ signals, etc. to/from the RF block, The decoder performs channel decoding (error and converts between analog and digital signals. correction) through deinterleaving and Viterbi/Turbo The CPU is a 32-bit RISC(M32R) that processes decoding and obtains the received data. communication protocol every 10ms frame, and uses DSP-2 Flash Viterbi/Turbo decoding Convolutional/Turbo encoding ROM + Deinterleave Interleave PSRAM CH decoder CH encoder CPU Finger Spreading Searcher Nyquist filter Demodulator Modulator RF DSP-1 APL AFE(Analog Front End) Fig. 1 Baseband modem LSI Mitsubishi Electric ADVANCE June 2005 3 TECHNICAL REPORTS A typical example is shown below to describe the hardware accelerator has various computing units characteristics of this LSI. operating in parallel, which enables hierarchical clock Figure 2 shows measurement results regarding the gating to effectively reduce the operating current. performance in the birth-death propagation condition at RMC12.2kbps (see 3GPP TS25.101 Annex B B.2.4). The required DPCH_Ec/Ior that satisfies BLER=1E-2 has secured a 3.4dB margin from 3GPP specification. Generally speaking, securing such characteristics and lowering power consumption by reducing circuit volume are considered contradictory, but through effi- cient algorithm techniques and other factors, this LSI achieves a fair level of demodulator performance. 3. Low Power Technology Table 1 shows the targets and achievements in extending talk time and standby time. Compared to the previous model (D2101V), the targets were set to two or three times longer for the talk time, and six to ten times longer for the standby time. The low power tech- nologies applied to achieve these targets with reduced Fig. 2 RMC12.2kbps birth-death performance talk/standby current are described below. Table 1 Targets and achievements of low power LSI 3.1 Talk Current Reduction Item Previously Target Results (D900i) This LSI contributes to reduce talk current mainly in terms of operating current (charge/discharge current Talk time (voice) 60 min x 2-3 170 min for the internal circuit), which is calculated using the Talk time (videophone) 50 min (ditto) 90 min 550 hrs following formula. Standby time 55 hrs x 6-10 (stationary) Operating current(I) 420 hrs (moving) ~ Quantity of electric charge (Q) x Time(t) ~ Capacity(C) x Voltage(V) x Time(t) The following (1)-(3) techniques were applied to reduce the operating current. CLK Function level (1) Reduction of capacity(C) Optimized the algorithm and required memory size A for each function, and reduced the hardware volume to fit into one chip. (2) Shortening of time(t) Block level B Thoroughly applied clock gating technique to each circuit and reduced the circuit operation time. Circuit level C (3) Reduction of voltage (V) Applied the optimized semiconductor process, and A Off On reduced the internal power voltage from 1.8V to 1.5V. B As results of these techniques, the operating cur- rent for baseband modem processing, which previously C accounted for about 35%-40%(200mA) of total talk, current was reduced by 85%. Figure 3 shows the clock gating technique applied Fig. 3 Clock gating technique here. For example, the processor turns the operating clock on/off at function level (Signal A), and the block 3.2 Standby Current Reduction control sequencer of each function turns the operating Other than (1)-(3) in Section 3.1 Talk Current Re- clock on/off (Signal B) at block level, and the circuit duction, the following (4)-(5) techniques were applied to sequencer of each block turns the operating clock reduce the standby current. on/off at circuit level (Signal C). Unlike the type of proc- (4) Shortening of standby processing time essor that shares and repeatedly uses a small number Modified the software to reduce standby process- of computing units or registers, this type of hardware ing time in communication control. 4 TECHNICAL REPORTS Figure 4 shows an example of observing such Thus, D900i equipped with this LSI has attained a current profile during standby time (receiving PICH + performance level of approx. 170/90 minutes for con- acquiring SFN). The upper three signals indicate oper- tinuous talk and approx. 550/420 hours for continuous ating status of DSP-2, DSP-1 and the CPU respectively. standby in stationary/moving states respectively. (The DSP operates at L level; the CPU at H level.) The lower signal reflects current waveform. Each processor was activated when necessary. By shortening the DSP-2 processing time in this way, the operating current of communication control, which previously accounted for over 60%(7mA) of total standby current, was reduced DSP-1 by 90%. CPU (5) Reduction of leak current Partly turned off the internal power of the LSI, which reduced the leak current by half. About half of the chip area of this LSI is used for the hardware accelerator, and the power for this part of the chip is turned off while operation is not required during standby. Current 4. Conclusion Mitsubishi Electric Corporation has developed a low power baseband modem LSI for W-CDMA mobile phones. Fig. 4 Example of observed current profile To extend talk time, talk current was reduced by means of (1) minimizing hardware (to fit into one chip) References by optimizing the algorithm and the required memory  Takahisa Aoyagi, Takahiko Nakamura, Yasuhiro size for each function; (2) shortening the circuit opera- Yano, and Kazuaki Ishioka: "Baseband modem tion time by thoroughly applying a clock gating tech- technology for W-CDMA mobile phones", MITSU- nique to each circuit; and (3) decreasing the internal BISHIDENKIGIHO, Vol.77, No.2, 11(121) ~ 14(124) power voltage of the LSI (from 1.8V to 1.5V) through (2003) optimizing the semiconductor process. Moreover, the  Toyohiko Yoshida, Masayuki Yamamoto, Takahiro standby time was extended with reduced standby cur- Kanbara, and Ryosuke Takeuchi: "Baseband LSI rent by means of (4) shortening the processing time by for W-CDMA mobile phones", MITSUBISHIDEN- modifying the software for standby processing in KIGIHO, Vol.77, No.2, 15(125) ~ 18(128) (2003) communications control; (5) reducing the leak current by partly turning on/off the internal power of the LSI; etc. By applying such techniques to lower power con- sumption, the operating current for baseband modem processing, which previously accounted for about 35-40%(200mA) of talk current, was reduced by 85%. Also, the operating current for the communication con- trol, which previously accounted for over 60% (7mA), was reduced by 90%. Mitsubishi Electric ADVANCE June 2005 5
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