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MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Current information @www.mot.com.sps/ADC
MC92307
Advance Information
2K - Samples FFT-Processor
RESB CLK SYMSYNC
The MC92307 is a pipelined Fast Fourier Transformation (FFT) processor with a blocklength of 2048 complex samples. It is especially designed for use in digital terrestrial Set-Top boxes according to the DVB-T standard for 2K transmission. One block of 2048 complex samples can be processed in 224 s Feature Summary * * * * * * * * * * Processing of one block of 2048 complex samples (i.e. one 2K-OFDM symbol) in 224 s. Designed for direct interfacing with Motorola's OFDM demodulator MC92308. Input wordlength 8 bit, output accuracy selectable between 10 and 12 bit. Overflow on certain OFDM subcarriers due to co-channel interferes is handled internally. Readout of output samples can be shifted by half the blocklength to start at the middle of the output block. Either multiplexed or non-multiplexed input and output format (the multiplexed mode allows direct interfacing with Motorola's OFDM Demodulator MC92308). Internal Bit reversal can be disabled to allow the construction of FFT modules for blocklengths > 2K by using several devices in parallel. Low clock rate inputs and outputs. 0.5m CMOS process at 3.3 V. 5 V tolerant inputs and outputs.
DOUT[11:0]
DOUTR[11:0]
NOMUX OFFSET
RES[1:0] FFTSTART
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DIN[7:0]
DINR[7:0]
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Ordering Information
In
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Device MC92307CI
Package 160QFP
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NOMUX DIN 8
in
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12
DOUT
DINR
8
Input Buffer
16
FFT (11 stages) incl. Rounding
24
Pr
FFTSTART
Output Reorder Buffer
12
DOUTR
RESB
CLK
Twiddle Factor ROM Control
FFTSTART SYMSYNC
OFFSET RES[1:0] REVRSB
Figure 1. Block diagram of the FFT processor MC92307
This document contains information on a new product. Specifications and information herein are subject to change without notice.
(c) MOTOROLA, INC. 1997 8/12/97
External Interfaces
Fast Fourier Transform in the DVB-T System
Within the DVB consortium several standards for digital television broadcast were submitted for the different transmission media, leading to DVB-S (satellite), DVBC (cable) and DVB-T (terrestrial). The details of the DVB-T system are described in reference [1]. To cope with the special effects of digital terrestrial transmission the OFDM modulation scheme was chosen: In principle the whole available bandwidth is divided into a large number N (e.g. 2048) of separate narrowband subchannels (the OFDM subcarriers). Data associated with each subcarrier are transmitted independently from and in parallel with the other subcarriers, leading to a very low datarate on each subcarrier compared to the overall transmission capacity. The superposition of all the subcarriers in the transmitter is achieved very efficiently by an IFFT. Consequently the corresponding functional block in the receiver is a FFT. This IFFT -> FFT pair is one of the central elements in all OFDM systems, it represents the link between the so-called frequency domain and the time domain used for the RF link between the transmitter and the receiver. Therefore one of the important parameters describing an OFDM system is the blocklength of the IFFT/FFT, such a block is called an `OFDM symbol'. OFFSET After the completion of the FFT processing the frequency domain data are output by the reorder buffer, starting together with a pulse of the SYMSYNC pin. The starting position of the output can be selected with the OFFSET pin. With OFFSET set to L the first frequency domain sample of a block that is delivered at the output of the FFT device belongs the baseband frequency corresponding to the DC component (i.e. the center frequency in the received time domain signal). The numbers of the frequency bins increases continuously until bin #2047 at the end of the block. If OFFSET is set to H the first frequency domain sample belongs to the baseband frequency bin #1024, corresponding to an offset of one half of the block (i.e. the DC component in the received time domain signal). Again the bin numbers increase up to bin #2047. Then a wraparound to bin #0 occurs.
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Sample # after SYMSYNC
s0 s1 ...
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Table 1. Function of OFFSET (Baseband) Bin # (OFFSET = L) (Baseband) Bin # (OFFSET = H)
DOUT1024 DOUT1025 ... DOUT2046 DOUT2047 DOUT0 ... DOUT1022 DOUT1023
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s1022 sd1023 s1024 ... s2046 s2047
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In the DVB-T specification two modes are described, the first with 2048 (2K) complex samples per OFDM symbol, the second with 8192 (8K) samples per block. The MC92307 device described here is designed especially for the use in systems working according in the 2K-mode described in reference [1].
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External Interfaces Control Interface
CLK Note that the bin numbers given in the table above correspond to the baseband positions. NOMUX The input interface (DIN and DINR) and the output interface (DOUT and DOUTR) can be used in two modes: Normally the complex samples are provided in the MULTIPLEXED mode, i.e. at first the real part of one sample is transferred using the DIN or DOUT lines followed by the imaginary part of the same sample using the same physical pins. The pins labelled DINR and DOUTR pins are not used, DINR should be tied to a fixed value and DOUTR should be left unconnected. The multiplexed mode is selected by setting the NOMUX line at L level, note that it is the only mode the FFT device MC92307 can be used together with the OFDM device MC92308.
The overall OFDM transmission clock of app. 36.57 MHz must be provided at this pin. Obviously in case of a DVB-T frontend composed of a MC92308 together with the MC92307 both devices have to be supplied with the same clock signal. Normally the 36.57 MHz are generated by a VCXO in the tuner which in turn is controlled by the OFDM timing synchronization circuitry. RESB Synchronous Reset: Normally H, a L together with a rising edge at CLK puts all outputs in tri-state and aborts any processing, leaving the FFT device in the idle mode.
MOTOROLA 2
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... ...
DOUT0 DOUT1 DOUT1022 DOUT1023 DOUT1024 DOUT2046 DOUT2047
MC92307_DS - 8/12/97
External Interfaces
If NOMUX is set to H the real and imaginary part of one sample is transferred in parallel using the DINR and DOUTR lines for the real part and the DIN and DOUT lines for the imaginary part. Consequently the transfer rate is divided by 2 compared to the muxed mode at the cost of more interconnection lines. Therefore this mode is intended mainly for use with external devices that operate on lower rates. REVRSB To achieve the output of the frequency domain data in natural order an internal bit reversal is done in the output reorder buffer. This bit reversal can be switched off e.g. to allow the combination of 4 MC92307 devices together with an external final radix-4 butterfly stage to do an 8K-FFT. RES[1:0] These two lines support the selection of the wordlength at the FFT output:
Table 2. Output resolution selection RES[1:0]
00 01 10 11
DOUT[11:0]
[0, 0, d9, d8, ... ,d0, ] [0, d10, d9, d8, ... ,d0, ] [d11, d10, d9, d8, ... ,d0, ] Don't care
OFDM Device -> FFT Device
The figures below illustrate the input of the time domain data into the FFT device and the output of the calculated frequency domain data after the completion of the FFT. The samples belonging to the real part are denoted by ...r (real), the imaginary samples are marked with ...q (quadrature). Figure 2 applies for the Multiplexed mode, Figure 3 is valid for the Non-multiplexed mode.
In
CLK X0r X0q X1r
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...
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FFTSTART Z(N-i)r
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DIN
X1q
Xir
Xq
X(i+1)r X(i+1)q
...
DOUT
Z(N-i)q Z(N-i+1)rZ(N-i+1)q
...
Z0r
Z0q
Z1r
Z1q
...
SYMSYNC
Pr
Figure 2. FFT Data I/O for the Multiplexed Mode
MC92307_DS - 8/12/97
MOTOROLA 3
External Interfaces
CLK X0r X1r
DINR
... ...
Xir
X(i+1)r
... ...
DIN
X0q
X1q
Xiq
X(i+1)q
FFTSTART Z(N-i)r Z(N-i+1)r
DOUTR
... ...
Z0r
Z1r
... ...
DOUT
Z(N-i)q
Z(N-i+1)q
Z0q
Z1q
SYMSYNC
Figure 3. Data I/O for the Non-multiplexed Mode
DINR [7:0]
In the non-muxed mode (NOMUX = H) the real part of the input samples is entered into the FFT device via these pins (they should be connected to a fixed level if the muxed mode is used). As the DIN inputs these inputs expect 2's complement format.
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These pins accept the input data with a wordlength of 8 bit. In the muxed mode first the real part of a sample must be provided followed by the imaginary part. In the non-muxed mode only the imaginary part must be delivered to DIN. The data format is fixed to 2's complement.
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DIN [7:0]
In
The input of a data block into the FFT device starts with a pulse of the FFTSTART signal. It must be delivered together with the real part of the first time domain sample and should last 1..2 clock cycles.
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SYMSYNC The start of the output of a FFT block after processing is indicated by a pulse of the SYMSYNC signal with a duration of 2 clock cycles. It is delivered together with the real part of the first output sample. DOUT [11:0] These pins deliver the output data of the FFT device in 2's complement format. In the non-muxed mode (NOMUX = H) the real part of the samples is followed by the imaginary part. In the muxed mode only the imaginary parts appears at the DOUT pins.The valid bits are adjusted using the RES pins, see above. DOUTR [11:0] In the non-muxed mode (NOMUX = H) the real part of the output samples appears at these pins in 2's complement format. The wordlength selection by the RES pins is also valid for DOUTR. If the non-muxed mode is used these pins may be left unconnected.
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FFTSTART
FFT Device -> OFDM Device
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MC92307_DS - 8/12/97
Pinout
Motorola's FFT device is packaged into a 160QFP package. The pinout of this package as well as the input and output lines are given in Figure 4 and Table 3. The supply voltage of the IC is 3.3 V, its power consumption will be app. 0.75 W in a typical DVB-T application as it is described in "Application Information'.
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MC92307_DS - 8/12/97
DINR3 DINR2 VDD DINR1 DINR0 VSS DIN7 DIN6 DIN5 VDD DIN4 DIN3 DIN2 VSS DIN1 DIN0 FFTSTART SYMSYNC DOUT11 VDD VSS DOUT10 DOUT9 DOUT8 DOUT7 VDD DOUT6 DOUT5 DOUT4 DOUT3 VSS DOUT2 DOUT1 DOUT0 VDD DOUTR11 DOUTR10 VSS DOUTR9 DOUTR8
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reserved (open) reserved (open) reserved (open) VDD reserved (open) reserved (open) reserved (open) VDD reserved (open) VSS reserved (open) reserved (open) reserved (open) reserved (open) reserved (open) VSS reserved (open) reserved (open) reserved (open) reserved (open) VDD reserved (open) reserved (open) reserved (open) reserved (open) VSS reserved (open) CLK reserved (VSS) reserved (open) VSS reserved (open) reserved (open) OFFSET VDD DINR7 DINR6 VSS DINR5 DINR4
reserved (open) reserved (open) VSS reserved (open) reserved (open) reserved (VSS) reserved (VSS) VDD reserved (VSS) reserved (VSS) VSS reserved (VSS) reserved (VSS) reserved (VSS) VDD reserved (VSS) reserved (VSS) reserved (VSS) RESB REVRSB reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) VSS reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) VDD reserved (VSS) reserved (VSS) reserved (VSS) VSS reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS)
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Figure 4. Pinout of the MC92307
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160QFP
reserved (VSS) VDD reserved (VSS) reserved (VSS) reserved (VSS) VSS reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) VDD reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) reserved (VSS) VSS reserved (VSS) reserved (VSS) reserved (VSS) VDD VSS reserved (VSS) RES1 RES0 NOMUX DOUTR0 DOUTR1 VDD DOUTR2 DOUT3 VSS DOUTR4 DOUTR5 VDD DOUTR6 DOUTR7
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MOTOROLA 5
Pinout
Table 3. MC92307 Pin Description of the FFT device SIGNAL
RESB CLK REVRSB DIN[7:0] RES[1:0] OFFSET FFTSTART DOUT[11:0] SYMSYNC NOMUX DINR[7:0] DOUTR[11:0]
FUNCTIONALITY
Synchronous Reset (active low) 36.57 MHz clock Enable bit reversal (active low) Complex data input muxed (real component first) Output resolution selection Selection of half symbol rotation in output Input frame start Complex data output muxed (real component first) Output frame start Selection of non-multiplexed data busses Complex data input (real part) if NOMUX = 1 Complex data output (real part) if NOMUX = 1
MOTOROLA 6
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MC92307_DS - 8/12/97
Package Data
The mechanical dimensions of the 160QFP package that is used for the FFT device are shown below:
NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DATUM PLANE -H- IS LOCATED AT BOTTOM OF LEAD AND IS COINCIDENT WITH THE LEAD WHERE THE LEAD EXITS THE PLASTIC BODY AT THE BOTTOM OF THE PARTING LINE. 4. DATUMS -A-, -B- AND -D- TO BE DETERMINED AT DATUM PLANE -H-. 5. DIMENSIONS S AND V TO BE DETERMINED AT SEATING PLANE -C-. 6. DIMENSIONS A AND B DO NOT INCLUDE MOLD PROTRUSION. ALLOWABLE PROTRUSION IS 0.25 (0.010) PER SIDE. DIMENSIONS A AND B DO INCLUDE MOLD MISMATCH AND ARE DETERMINED AT DATUM PLANE -H-. 7. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.08 (0.003) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. DAMBAR CANNOT BE LOCATED ON THE LOWER RADIUS OR THE FOOT.
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MC92307_DS - 8/12/97
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Figure 5. Mechanical Data of the 160QFP Package
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MOTOROLA 7
Application Information
As already mentioned the FFT device is especially suited to be combined with Motorola's OFDM device MC92308 to form the complete digital part of a frontend for a 2K DVB-T receiver. Refer to Figure 6 for the functional blocks of a terrestrial DVB receiver. Further details of the blocks are given in reference [2]. One of the key signals for the successful reception of an OFDM signal is the correct timing synchronization, that means that the synchronization circuitry chooses the correct starting point to trigger the FFT operation. Therefore the OFDM demodulator MC92308 provides the FFTSTART signal to the FFT device. If 2048 complex time domain samples have been read into the input buffer the FFT operation starts. Its result is flagged with the SYMSYNC line and the calculated frequency domain samples are output to the OFDM device that continues with the demodulation process.
MC92307 2k-FFT
8
12
IC HC05 uC
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DVALID
Tuner Core
D
8
CLKEN18
MC92308 OFDM
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16
A
FFTDO RESB ADCDATA
FFT START
SYMSYNC FFTDI MBUS uP IF
1/2
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FECCLK G1DATA G2DATA
CLK
VCO
Tuner
MOTOROLA 8
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Figure 6. Application Example for the OFDM and FFT Devices
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CLK CLK CTLP CTLN
AGC AGC CTLP CTLN
3 3
MC92309 FEC
8
MPEG Clock MPEG-2 Transport Stream
MC92307_DS - 8/12/97
Switching Characteristics
In the following diagram together with the associated table the characteristics of the interface for the FFT data is given. Note that they are valid for temperatures between 0C and 80C and a supply voltage range of 3.0 V - 3.6 V
7
CLK
2 1
FFTSTART
3 4 I0 5 5 I0 4 Q0 4 4 Q0
6
6 I0
fo r
SYMSYNC
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6 Q0 6 Q0
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DIN
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min max 1.4 3.1 2.3 3.5 4.6 3.6 27.4 13.1 11.8
6
Figure 7. Timing Characteristic of the FFT Device
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No. 1 2 3 4 5 6 7
Pr
Characteristic FFTSTART to CLK setup time FFTSTART to CLK hold time Data in to CLK setup time Data in to CLK hold time CLK to SYMSYNC out delay CLK to Data out delay CLK period
in
Table 4. Timing Data for the FFT Device
unit ns ns ns ns ns ns ns
MC92307_DS - 8/12/97
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DOUT
In
I0
MOTOROLA 9
References
[1] Digital broadcasting systems for television, sound and data services; Framing structure, channel coding and modulation for digital terrestrial television. Draft prETS 300 744 published by ETSI September 1996. [2] MC92308 OFDM Demodulator, Product Data Sheet for the MC92308.
Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. "Typical" parameters which may be provided in Motorola data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. Motorola does not convey any license under its patent rights nor the rights of others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury or death may occur. Should Buyer purchase or use Motorola products for any such unintended or unauthorized application, Buyer shall indemnify and hold Motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal Opportunity/Affirmative Action Employer.
How to reach us: USA/EUROPE/Locations Not Listed: Motorola Literature Distribution; P.O. Box 5405, Denver Colorado 80217. 1-800-441-2447 or 303-675-2140 MFaxTM: RMFAX0@email.sps.mot.com -TOUCHTONE (602) 244-6609 INTERNET:http://mot-sps.com/sps/General/sales.html
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JAPAN: Nippon Motorola Ltd.; Tatsumi-SPD-JLDC, 6F Seibu-Butsuryu-Center, 3-14-2 Tatsumi Koto-Ku, Tokyo 135, Japan. 81-3-3521-8315 ASIA/PACIFIC: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park, 51 Ting Kok Road, Tai Po, N.T., Hong Kong. 852-26629298
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MC92307_DS - 8/12/97

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