JPWO2013042249A1 - Fast Fourier transform circuit - Google Patents

Abstract

A plurality of data strings parallel on the time axis are subjected to FFT processing by a small circuit. The multiplexer (11) receives a plurality of data strings parallel on the time axis, outputs partial data of each data string in order of a predetermined data string for each unit time, and the first stage butterfly operation unit (12-1) The partial data output from the multiplexer (11) is input as second input data, and the delay unit (13-1) provided corresponding to the first stage butterfly calculation unit (12-1) is connected to the multiplexer (11). Are output in the order of the data string, and output as the first input data of the first stage butterfly operation unit (12-1) with a delay.

Description

  The present invention relates to a fast Fourier transform circuit.

Pipeline type fast Fourier transform (hereinafter referred to as FFT) circuits are applied in a wide range of industrial fields such as wired or wireless communication devices, AV (Audio / Visual) devices, and the like.
Conventionally, when processing stream data of a plurality of channels, which are a plurality of data strings arranged in parallel on the time axis, a single pipeline type FFT circuit is used, and the input is switched by SISO (Single Input Single Output). Data processing was performed for each channel. However, in recent years, as represented by wireless MIMO (Multi Input Multi Output), there is an increasing demand to simultaneously process stream data of a plurality of channels.

  As a technique for simultaneously processing stream data of a plurality of channels, a technique of providing a pipeline type FFT circuit for each channel and independently processing the stream data of a plurality of channels in each FFT circuit is known.

JP-A-6-342449

  However, the conventional FFT circuit for processing a plurality of stream data has a problem that the circuit scale becomes large because a pipeline type FFT circuit is provided for each channel.

  According to one aspect of the invention, a multiplexer that receives a plurality of data strings parallel on the time axis and outputs partial data of each data string in a predetermined data string order for each unit time, and delays the input data A plurality of delay units to be output and a plurality of stages corresponding to the plurality of delay units are provided, and the output data of the corresponding delay unit is input as first input data, and the sum and difference with the second input data are calculated. A butterfly operation unit that calculates and outputs one operation result or the second input data to the corresponding delay unit, the other operation result of the butterfly operation unit or the output data of the corresponding delay unit, and a twiddle factor And a multiplication unit that outputs the second input data of the butterfly computation unit in the subsequent stage, and the butterfly computation unit in the first stage outputs the partial data output from the multiplexer. A delay unit provided corresponding to the first butterfly operation unit among the plurality of delay units, the partial data output by the multiplexer in the order of the data string. A fast Fourier transform circuit is provided that inputs and delays and outputs the first input data of the first butterfly computation unit.

According to the disclosed fast Fourier transform circuit, a plurality of stream data can be subjected to FFT processing with a small-scale circuit.
These and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments by way of example of the present invention.

It is a figure which shows an example of the FFT circuit in this Embodiment. It is a figure which shows an example of stream data. It is a figure which shows the state of an example of the signal of each part of an FFT circuit when a multiplication clock signal rises 12 times. It is a figure which shows the state of an example of the signal of each part of an FFT circuit when a multiplication clock signal rises 18 times. It is a figure which shows the state of an example of the signal of each part of an FFT circuit when a multiplication clock signal rises 21 times. It is a figure which shows the state of an example of the signal of each part of an FFT circuit when a multiplication clock signal rises 22 times. It is a figure which shows the state of an example of the signal of each part of an FFT circuit when a multiplication clock signal rises 23 times.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an example of an FFT circuit in this embodiment.
The FFT circuit 10 includes a multiplexer 11, butterfly operation units 12-1, 12-2, and 12-3, delay units 13-1, 13-2, and 13-3, multiplication units 14-1 and 14-2, and twiddle factor generation. Units 15-1 and 15-2, a multiplier circuit 16, a counter 17, and a control unit 18.

  The FFT circuit 10 of the present embodiment is a pipeline-type FFT circuit that performs Fourier transform using butterfly computation. Although a detailed description of the calculation algorithm is omitted, in a pipeline type FFT, an operation is performed by dividing the FFT data length into its divisors. When the data length is 8, it can be expressed as 8 = 2 × 2 × 2, and therefore, the FFT operation is performed in three stages (8), which are divisors of 8, and the data length is 8, 4, and 2. The FFT circuit 10 shown in FIG. 1 shows an example in which the FFT data length is 8, but the present invention is not limited to this.

  The multiplexer 11 receives a plurality of data strings (hereinafter referred to as stream data) that are parallel on the time axis. In the example illustrated in FIG. 1, the multiplexer 11 receives three stream data from the input signal lines IN1, IN2, and IN3.

FIG. 2 is a diagram illustrating an example of stream data. The horizontal axis is the time axis.
FIG. 2 shows an example of three stream data SD1, SD2, and SD3. The stream data SD1 has partial data x0, x1, x2,..., Xn, the stream data SD2 has partial data y0, y1, y2,..., Yn, and the stream data SD3 has partial data z0, z1. , Z2,..., Zn. The data amount of each partial data is, for example, one word. The types of the stream data SD1 to SD3 are, for example, image data, audio data, etc., and are not particularly limited.

  For example, the multiplexer 11 receives the stream data SD1 via the input signal line IN1, receives the stream data SD2 via the input signal line IN2, and receives the stream data SD3 via the input signal line IN3. The stream data SD1 to SD3 are supplied from the outside of the FFT circuit 10 in synchronization with the clock signal. The multiplexer 11 outputs partial data of each stream in a predetermined stream data order for each unit time.

  For example, the multiplexer 11 outputs one partial data of each stream data SD1 to SD3 for each unit time in the order of the stream data SD1, SD2, and SD3. For example, the multiplexer 11 that receives the stream data SD1 to SD3 as shown in FIG. 2 outputs in the order of the partial data x0, y0, z0, x1, y1, z1,..., Xn, yn, zn for each unit time. Do.

The unit time is a cycle of the clock signal whose frequency is multiplied by the number of stream data by the multiplier circuit 16.
The butterfly computing units 12-1 to 12-3 are provided in a plurality of stages corresponding to the delay units 13-1 to 13-3.

The number of stages of the butterfly operation units 12-1 to 12-3 and the delay units 13-1 to 13-3 depends on the number of partial data (FFT data length) of each of the stream data SD1, SD2, and SD3 to be subjected to FFT. Determined. When the number of partial data is 2 ³ = 8, as shown in FIG. 1, three stages of butterfly computing units 12-1 to 12-3 are provided. When the number of partial data is 2 ⁴ = 16, a four-stage butterfly operation unit is provided.

  The butterfly calculation units 12-1 to 12-3 receive the output data of the corresponding delay units 13-1 to 13-3 as the first input data, and calculate the sum and difference with the second input data. Then, the butterfly calculation units 12-1 to 12-3 output one calculation result or the second input data to the corresponding delay units 13-1 to 13-3.

  The butterfly calculation unit 12-1 includes a calculation unit 12a and selectors 12b and 12c. The arithmetic unit 12a receives the output data from the delay unit 13-1 through the terminal I1 and the partial data output from the multiplexer 11 through the terminal I2. And the calculating part 12a calculates the sum and difference of both, outputs a difference from terminal SUB, and outputs a sum from terminal ADD.

  The partial data output from the multiplexer 11 and the calculation result output from the terminal SUB of the calculation unit 12a are input to the selector 12b. The selector 12b selects one of the two input data according to the value of the bit output from the terminal Q2 of the control unit 18, and outputs the selected data to the delay unit 13-1. The selector 12b selects and outputs the partial data output from the multiplexer 11 when the bit output from the terminal Q2 of the control unit 18 is “0”, and the terminal of the arithmetic unit 12a when the bit is “1”. A calculation result output from the SUB is selected and output.

  The selector 12c receives the output data from the delay unit 13-1 and the calculation result output from the terminal ADD of the calculation unit 12a. The selector 12c selects one of the two input data according to the value of the bit output from the terminal Q2 of the control unit 18, and outputs it to the multiplication unit 14-1. The selector 12c selects and outputs the output data from the delay unit 13-1 when the bit output from the terminal Q2 of the control unit 18 is "0", and when the bit is "1", the selector 12c The calculation result output from the terminal ADD is selected and output.

  The butterfly computing units 12-2 and 12-3 also have the same circuit as the butterfly computing unit 12-1, but are not shown in FIG. However, in the butterfly calculation unit 12-2, the selector 12b inputs the calculation result of the multiplication unit 14-1 instead of the partial data output from the multiplexer 11. Further, in the butterfly calculation unit 12-3, the selector 12b inputs the calculation result of the multiplication unit 14-2 instead of the partial data output from the multiplexer 11.

The butterfly computing unit 12-3 at the last stage is connected to the output signal line OUT, and outputs the FFT result to the outside of the FFT circuit 10 via the output signal line OUT.
The delay units 13-1 to 13-3 output the input data with a delay, and a plurality of delay units 13-1 to 13-3 are provided corresponding to the number of stages of the butterfly calculation units 12-1 to 12-3. In the example of FIG. 1, three delay units 13-1 to 13-3 are provided.

  The delay unit 13-1 provided corresponding to the first stage butterfly operation unit 12-1 has a shift register 13a, and shifts the data taken in synchronization with the multiplied clock signal generated by the multiplication circuit 16. , Output after delaying by a predetermined delay time. The delay units 13-2 and 13-3 have similar shift registers, but are not shown in FIG.

  Also, the delay unit 13-1 inputs the partial data output from the multiplexer 11 in the order of the stream data described above, delays it, and outputs it as the first input data of the first stage butterfly operation unit 12-1. FIG. 1 shows a state in which partial data x0, y0, and z0 are stored in the shift register 13a of the delay unit 13-1 in this order.

  In the delay units 13-1 to 13-3 that output the first input data to the butterfly computing units 12-1 to 12-3, the delay time is as follows according to the number of stream data and the number of partial data. Is set to be That is, the delay time of both the first input data including the partial data of the same stream data as the partial data included in the second input data of the butterfly calculation units 12-1 to 12-3 is the butterfly calculation unit 12-1. ˜12-3 is set to be input.

  For example, when the partial data x4 of the stream data SD1 is input to the butterfly operation unit 12-1, the delay time is set so that the partial data x0 of the same stream data SD1 is output from the delay unit 13-1. .

  When the number of partial data is 8, three delay units 13-1 to 13-3 are provided, and the delay time is 4 × number of stream data × unit time in the delay unit 13-1. In the delay unit 13-2, the delay time is 2 × number of stream data × unit time, and in the delay unit 13-3, 1 × number of stream data × unit time.

  Therefore, when the number of stream data is 3, the delay time of the delay unit 13-1 is 12 × unit time, the delay time of the delay unit 13-2 is 6 × unit time, and the delay time of the delay unit 13-3 is 3 × unit time.

As a result, the butterfly computation units 12-1 to 12-3 at each stage can perform butterfly computation using partial data of the same stream data.
Depending on the selection result of the selector 12c, the multiplying units 14-1 and 14-2 receive one of the calculation results of the butterfly calculation units 12-1 and 12-2 or the output data of the delay units 13-1 and 13-2. , Multiply by the twiddle factor and output. The data output from the multiplying units 14-1 and 14-2 becomes the second input data of the butterfly computing units 12-2 and 12-3 at the subsequent stage.

  The twiddle factor generators 15-1 and 15-2 generate a twiddle factor (sometimes referred to as a twist factor). The twiddle factor generation units 15-1 and 15-2 update the twiddle factor according to the signal from the control unit 18. The twiddle factor is expressed by the following equation.

W _N ⁿ = (exp ^{−j (2} π ^{/ N)} ) ⁿ
In the above equation, N is the FFT data length of each stage. In the FFT circuit 10 of FIG. 1 that performs an FFT operation with a data length of 8, N = 8 in the twiddle factor generation unit 15-1 that generates a twiddle factor that multiplies the output of the first stage butterfly operation unit 12-1. In the twiddle factor generation unit 15-2 that generates the twiddle factor multiplied by the output of the second stage butterfly calculation unit 12-2, N = 4.

  N is a decimal stage state number and is determined by bits output from the terminals Q0, Q1, and Q2 of the control unit 18. Hereinafter, the bits output from the terminals Q0 to Q2 will be referred to as bits Q0 to Q2. Bit Q0 is the least significant bit and bit Q2 is the most significant bit.

The stage state number n takes a value of 0 to 7 when N = 8, and takes a value of 0 to 3 when N = 4.
For example, if the three bits Q2, Q1, and Q0 are binary numbers (000), n = 0 and W ₈ ⁰ = W ₄ ⁰ = 1. When N = 8, W ₈ ⁿ is “1” when n = 4 to 7, and when N = 4, W ₄ ⁿ is “1” when n = 2, 3. Has properties.

  The multiplier circuit 16 receives a clock signal that determines the input timing to the multiplexer 11 via the clock signal line CLK, and generates a multiplied clock signal by multiplying the frequency of the clock signal by the number of stream data. The period of the multiplied clock signal is the unit time described above. Therefore, conversely, it can be said that the clock signal has a cycle that is several times the number of stream data per unit time.

  The counter 17 generates a selection signal of the multiplexer 11 that is updated at the cycle of the multiplied clock signal, and also sends a control signal (hereinafter referred to as an enable signal) obtained by dividing the multiplied clock signal to the number of stream data to the control unit 18. Output function. When the number of stream data is 3, the counter 17 is a ternary binary counter, and counts the rising or falling edge of the multiplied clock signal, and the count value is 2 ((10) in binary notation). , “1” is output to the control unit 18.

  The counter 17 outputs the count value to the multiplexer 11 as a selection signal. Since the count value is updated at the cycle of the multiplied clock signal, the multiplexer 11 selects and outputs partial data of the stream data SD1 to SD3 at the cycle of the multiplied clock signal.

  The control unit 18 is a 3-bit binary counter when the number of partial data to be subjected to FFT is 8. The control unit 18 receives the enable signal output from the counter 17 at the terminal EN, and counts rising or falling edges of the multiplied clock signal input to the terminal CK when the enable signal is “1”. Then, the control unit 18 sends the most significant bit Q2 of the count value to the butterfly calculation unit 12-1 and the twiddle factor generation unit 15-1.

  Further, the control unit 18 sends the second bit Q1 of the count value to the butterfly calculation unit 12-2 and the twiddle factor generation units 15-1 and 15-2, and the least significant bit Q0 to the butterfly calculation unit 12-3. And sent to the twiddle factor generators 15-1 and 15-2.

Thereby, the twiddle factor generation units 15-1 and 15-2 can update the twiddle factor at the timing according to the enable signal (that is, the period of the original clock signal).
By using the FFT circuit 10 of this embodiment as described above, as will be described in detail below, a plurality of stream data is subjected to FFT in one pipeline type FFT circuit 10 for each partial data. It can be processed. That is, it is possible to perform FFT on a plurality of stream data with a small circuit.

  Also, in the FFT circuit 10 of the present embodiment, partial data is output from the multiplexer 11 at the cycle of the multiplied clock signal obtained by multiplying the frequency of the original clock signal by the number of stream data, and the twiddle factor is updated at the cycle of the clock signal. ing. Thereby, even a single pipelined FFT circuit 10 can perform FFT of a plurality of stream data at high speed.

Hereinafter, the operation of the FFT circuit 10 of the present embodiment will be described.
In the following description, it is assumed that three stream data SD1 to SD3 as shown in FIG. 2 are input from the outside of the FFT circuit 10 to the multiplexer 11 via the input signal lines IN1 to IN3. The FFT circuit 10 operates in synchronization with the rising timing of the clock signal or the multiplied clock signal.

  The multiplexer 11 receives the stream data SD1 to SD3 for each partial data in synchronization with the clock signal. First, the multiplexer 11 receives the first partial data x0, y0, z0 of the stream data SD1 to SD3 at a rising timing of the clock signal.

  In the initial state, the count value of the counter 17 is (00), and the multiplexer 11 using this count value as the selection signal selects and outputs the first partial data x0 of the stream data SD1. In the initial state, the bits Q2, Q1, and Q0 output from the control unit 18 are (000), and the selector 12b of the butterfly calculation unit 12-1 outputs the partial data x0.

When bits Q2, Q1, and Q0 are (000), as described above, the twiddle factor generated by twiddle factor generators 15-1 and 15-2 is “1”.
When the multiplied clock signal generated by the multiplier circuit 16 rises to the H (High) level, the count value of the counter 17 becomes (01). Thereby, the multiplexer 11 selects and outputs the first partial data y0 of the stream data SD2. Since the count value of the counter 17 is (01), the enable signal output from the counter 17 to the control unit 18 remains “0”. Therefore, the bits Q2, Q1, and Q0 output from the control unit 18 also remain (000), and the selector 12b of the butterfly calculation unit 12-1 outputs partial data y0.

  At this time, the shift register 13a of the delay unit 13-1 takes in the partial data x0 output from the butterfly operation unit 12-1 at the previous timing in synchronization with the rising edge of the multiplied clock signal.

  When the multiplied clock signal rises next time, the count value of the counter 17 becomes (10). Thereby, the multiplexer 11 selects and outputs the first partial data z0 of the stream data SD3. When the count value of the counter 17 is (10), the enable signal output from the counter 17 to the control unit 18 is “1”, but is output from the control unit 18 until the next multiplied clock signal rises. Bits Q2, Q1, and Q0 also remain (000). Therefore, the selector 12b of the butterfly calculation unit 12-1 outputs the partial data z0.

  At this time, the shift register 13a of the delay unit 13-1 shifts the already acquired partial data x0 to the subsequent register and acquires the partial data y0 in synchronization with the rising edge of the multiplied clock signal.

  When the multiplied clock signal rises next, the same processing is performed, the partial data z0 is taken into the shift register 13a, and the shift register 13a is in the state shown in FIG. In addition, since the multiplied clock signal is input while the enable signal is “1”, the control unit 18 counts and the bit Q0 becomes “1”. However, the bits Q1 and Q2 remain “0”. Therefore, in the butterfly operation unit 12-1, the selector 12b similarly selects the partial data x1 output from the multiplexer 11 and outputs the selected partial data x1 to the delay unit 13a.

When the above processing is repeated and the multiplied clock signal rises 12 times after the processing is started, the FFT circuit 10 is in a state as shown below.
FIG. 3 is a diagram illustrating a state of an example of a signal of each part of the FFT circuit when the multiplied clock signal rises 12 times. The multiplexer 11, the multiplier circuit 16, and the like shown in FIG. 1 are not shown. The multiplied clock signal is denoted as CLKM.

  When the multiplied clock signal CLKM rises 12 times, the shift register 13a enters the state shown in FIG. 3 and outputs the partial data x0. At this time, the calculation unit 12a of the butterfly calculation unit 12-1 calculates the sum (x0 + x4) and the difference (x0−x4) of the partial data x0 and the partial data x4 output from the multiplexer 11.

  Further, in the state where the multiplied clock signal CLKM rises 12 times, as a result of the count in the control unit 18 being advanced, the bits Q2, Q1, and Q0 are (100). Therefore, the selector 12b of the butterfly computation unit 12-1 outputs x0-x4 to the delay unit 13-1, and the selector 12c outputs x0 + x4 to the multiplication unit 14-1.

  Further, as described above, when the input bits Q2, Q1, and Q0 are (100), the twiddle factor generation unit 15-1 outputs “1”. Therefore, the multiplication unit 14-1 outputs x0 + x4. In the butterfly operation unit 12-2 at the next stage, the selector 12b outputs x0 + x4 to the delay unit 13-2 because the bit Q1 input as the selection signal is “0”.

  At this time, the outputs of the calculation units 12a of the butterfly calculation units 12-2 and 12-3 are not yet determined because the first input data supplied from the delay units 13-2 and 13-3 has not been determined. It is in the state of.

When the processing further proceeds and the multiplied clock signal CLKM rises 18 times after the processing is started, the FFT circuit 10 is in a state as shown below.
FIG. 4 is a diagram illustrating a state of an example of a signal of each part of the FFT circuit when the multiplied clock signal rises 18 times.

  When the multiplied clock signal CLKM rises 18 times, the shift register 13a enters the state shown in FIG. 4 and outputs the partial data x2. At this time, the calculation unit 12a of the butterfly calculation unit 12-1 calculates the sum (x2 + x6) and the difference (x2-x6) of the partial data x2 and the partial data x6 output from the multiplexer 11.

  Further, in the state where the multiplied clock signal CLKM rises 18 times, as a result of the count in the control unit 18 being advanced, the bits Q2, Q1, and Q0 are (110). Therefore, the selector 12b of the butterfly calculation unit 12-1 outputs x2-x6 to the delay unit 13-1, and the selector 12c outputs x2 + x6 to the multiplication unit 14-1.

  Further, as described above, the twiddle factor generation unit 15-1 outputs “1” even when the input bits Q2, Q1, and Q0 are (110). Therefore, the multiplication unit 14-1 outputs x2 + x6.

  When the multiplied clock signal CLKM rises 18 times, the shift register 13b of the delay unit 13-2 provided corresponding to the second stage butterfly calculation unit 12-2 is in a state as shown in FIG. x0 + x4 is output. At this time, the calculation unit 12a of the butterfly calculation unit 12-2 calculates the sum ((x0 + x4) + (x2 + x6)) and the difference ((x0 + x4) − (x2 + x6)) of x0 + x4 and x2 + x6 output from the multiplication unit 14-1. Is calculated.

  Since the bit Q1 output from the control unit 18 is “1”, the selector 12b of the butterfly operation unit 12-2 outputs (x0 + x4) − (x2 + x6) to the delay unit 13-2, and the selector 12c x0 + x4) + (x2 + x6) is output to the multiplier 14-2.

  The twiddle factor generator 15-2 outputs “1” when the input bits Q0 and Q1 are (10). Therefore, the multiplication unit 14-2 outputs (x0 + x4) + (x2 + x6). In the butterfly operation unit 12-3 in the next stage, the selector 12b outputs (x0 + x4) + (x2 + x6) to the delay unit 13-3 because the bit Q0 input as the selection signal is “0”.

  At this time, since the first input data to the butterfly computing unit 12-3 output from the delay unit 13-3 is not fixed, the output of the computing unit 12a of the butterfly computing unit 12-3 is still in an indefinite state. It has become.

When the processing further proceeds and the multiplied clock signal CLKM rises 21 times after the processing is started, the FFT circuit 10 is in a state as shown below.
FIG. 5 is a diagram illustrating a state of an example of a signal of each part of the FFT circuit when the multiplied clock signal rises 21 times.

  When the multiplied clock signal CLKM rises 21 times, the shift register 13a enters the state shown in FIG. 5 and outputs the partial data x3. At this time, the calculation unit 12a of the butterfly calculation unit 12-1 calculates the sum (x3 + x7) and the difference (x3-x7) of the partial data x3 and the partial data x7 output from the multiplexer 11.

  In addition, in the state where the multiplied clock signal CLKM has risen 21 times, as a result of the count in the control unit 18 being advanced, the bits Q2, Q1, and Q0 are (111). Therefore, the selector 12b of the butterfly calculation unit 12-1 outputs x3-x7 to the delay unit 13-1, and the selector 12c outputs x3 + x7 to the multiplication unit 14-1. The twiddle factor generator 15-1 also outputs “1” when the input bits Q2, Q1, and Q0 are (111) as described above. Therefore, the multiplication unit 14-1 outputs x3 + x7.

  When the multiplied clock signal CLKM rises 21 times, the shift register 13b of the delay unit 13-2 provided corresponding to the second stage butterfly calculation unit 12-2 is in a state as shown in FIG. x1 + x5 is output. At this time, the calculation unit 12a of the butterfly calculation unit 12-2 adds ((x1 + x5) + (x3 + x7)) and difference ((x1 + x5) − (x3 + x7)) between x1 + x5 and x3 + x7 output from the multiplication unit 14-1. Is calculated.

  Since the bit Q1 output from the control unit 18 is “1”, the selector 12b of the butterfly operation unit 12-2 outputs (x1 + x5) − (x3 + x7) to the delay unit 13-2, and the selector 12c x1 + x5) + (x3 + x7) is output to the multiplier 14-2.

  The twiddle factor generator 15-2 outputs “1” when the input bits Q0 and Q1 are (11). Therefore, the multiplication unit 14-2 outputs (x1 + x5) + (x3 + x7).

  When the multiplied clock signal CLKM rises 21 times, the shift register 13c of the delay unit 13-3 provided corresponding to the third stage (last stage) butterfly operation unit 12-3 is as shown in FIG. State, and (x0 + x4) + (x2 + x6) is output. At this time, the calculation unit 12a of the butterfly calculation unit 12-3 calculates the sum and difference of (x0 + x4) + (x2 + x6) and (x1 + x5) + (x3 + x7) output from the multiplication unit 14-2. The sum is ((x0 + x4) + (x2 + x6)) + ((x1 + x5) + (x3 + x7)), and the difference is ((x0 + x4) + (x2 + x6)) − ((x1 + x5) + (x3 + x7)).

  Since the bit Q0 output from the control unit 18 is “1”, the selector 12b of the butterfly operation unit 12-3 outputs ((x0 + x4) + (x2 + x6)) − ((x1 + x5) + (x3 + x7)) as a delay unit. Output to 13-3. The selector 12c outputs ((x0 + x4) + (x2 + x6)) + ((x1 + x5) + (x3 + x7)) as the first value of the FFT result of the stream data SD1.

Next, when the multiplied clock signal CLKM rises, the FFT circuit 10 is in a state as shown below.
FIG. 6 is a diagram illustrating a state of an example of a signal of each part of the FFT circuit when the multiplied clock signal rises 22 times.

  When the multiplied clock signal CLKM rises 22 times, the shift register 13a enters the state shown in FIG. 6 and outputs partial data y3. At this time, the computing unit 12a of the butterfly computing unit 12-1 calculates the sum (y3 + y7) and the difference (y3-y7) of the partial data y3 and the partial data y7 output from the multiplexer 11.

  In addition, when the multiplied clock signal CLKM rises 22 times, the enable signal is “0”, so the bits Q2, Q1, and Q0 output from the control unit 18 remain (111). Therefore, the selector 12b of the butterfly calculation unit 12-1 outputs y3-y7 to the delay unit 13-1, and the selector 12c outputs y3 + y7 to the multiplication unit 14-1. Since the twiddle factor generation unit 15-1 outputs “1”, the multiplication unit 14-1 outputs y3 + y7.

  When the multiplied clock signal CLKM rises 22 times, the shift register 13b of the delay unit 13-2 provided corresponding to the second stage butterfly operation unit 12-2 outputs y1 + y5. At this time, the computation unit 12a of the butterfly computation unit 12-2 calculates the sum ((y1 + y5) + (y3 + y7)) and difference ((y1 + y5) − (y3 + y7)) of y1 + y5 and y3 + y7 output from the multiplication unit 14-1. Is calculated.

  Since the bit Q1 output from the control unit 18 is “1”, the selector 12b of the butterfly operation unit 12-2 outputs (y1 + y5) − (y3 + y7) to the delay unit 13-2, and the selector 12c ( y1 + y5) + (y3 + y7) is output to the multiplier 14-2.

Further, since the twiddle factor generation unit 15-2 outputs “1”, the multiplication unit 14-2 outputs (y1 + y5) + (y3 + y7).
When the multiplied clock signal CLKM rises 22 times, the shift register 13c of the delay unit 13-3 provided corresponding to the butterfly operation unit 12-3 outputs (y0 + y4) + (y2 + y6). At this time, the calculation unit 12a of the butterfly calculation unit 12-3 calculates the sum and difference of (y0 + y4) + (y2 + y6) and (y1 + y5) + (y3 + y7) output from the multiplication unit 14-2. The sum is ((y0 + y4) + (y2 + y6)) + ((y1 + y5) + (y3 + y7)), and the difference is ((y0 + y4) + (y2 + y6)) − ((y1 + y5) + (y3 + y7)).

  Since the bit Q0 output from the control unit 18 is “1”, the selector 12b of the butterfly operation unit 12-3 outputs ((y0 + y4) + (y2 + y6)) − ((y1 + y5) + (y3 + y7)) as a delay unit. Output to 13-3. The selector 12c outputs ((y0 + y4) + (y2 + y6)) + ((y1 + y5) + (y3 + y7)) as the first value of the FFT result of the stream data SD2.

Next, when the multiplied clock signal CLKM rises, the FFT circuit 10 is in a state as shown below.
FIG. 7 is a diagram illustrating a state of an example of a signal of each part of the FFT circuit when the multiplied clock signal rises 23 times.

  When the multiplied clock signal CLKM rises 23 times, the shift register 13a outputs partial data z3. At this time, the calculation unit 12a of the butterfly calculation unit 12-1 calculates the sum (z3 + z7) and the difference (z3-z7) of the partial data z3 and the partial data z7 output from the multiplexer 11.

  In the state where the multiplied clock signal CLKM rises 23 times, the enable signal becomes “1”, but the bits Q2, Q1, and Q0 output from the control unit 18 are (111) until the next multiplied clock signal CLKM rises. ). Therefore, the selector 12b of the butterfly calculation unit 12-1 outputs z3-z7 to the delay unit 13-1, and the selector 12c outputs z3 + z7 to the multiplication unit 14-1. Since the twiddle factor generation unit 15-1 outputs “1”, the multiplication unit 14-1 outputs z3 + z7.

  When the multiplied clock signal CLKM rises 23 times, the shift register 13b of the delay unit 13-2 provided corresponding to the second stage butterfly operation unit 12-2 outputs z1 + z5. At this time, the calculation unit 12a of the butterfly calculation unit 12-2 calculates the difference ((z1 + z5) − (z3 + z7)) between the sum ((z1 + z5) + (z3 + z7)) of z1 + z5 and z3 + z7 output from the multiplication unit 14-1. Is calculated.

  Since the bit Q1 output from the control unit 18 is “1”, the selector 12b of the butterfly operation unit 12-2 outputs (z1 + z5) − (z3 + z7) to the delay unit 13-2, and the selector 12c ( z1 + z5) + (z3 + z7) is output to the multiplier 14-2.

Further, since the twiddle factor generation unit 15-2 outputs “1”, the multiplication unit 14-2 outputs (z1 + z5) + (z3 + z7).
When the multiplied clock signal CLKM rises 23 times, the shift register 13c of the delay unit 13-3 provided corresponding to the butterfly operation unit 12-3 outputs (z0 + z4) + (z2 + z6). At this time, the calculation unit 12a of the butterfly calculation unit 12-3 calculates the sum and difference of (z0 + z4) + (z2 + z6) and (z1 + z5) + (z3 + z7) output from the multiplication unit 14-2. The sum is ((z0 + z4) + (z2 + z6)) + ((z1 + z5) + (z3 + z7)), and the difference is ((z0 + z4) + (z2 + z6)) − ((z1 + z5) + (z3 + z7)).

  Since the bit Q0 output from the control unit 18 is “1”, the selector 12b of the butterfly operation unit 12-3 outputs ((z0 + z4) + (z2 + z6)) − ((z1 + z5) + (z3 + z7)) as a delay unit. Output to 13-3.

In addition, the selector 12c outputs ((z0 + z4) + (z2 + z6)) + ((z1 + z5) + (z3 + z7)) as the first value of the FFT result of the stream data SD3.
With the processing so far, the first FFT result of the stream data SD1 to SD3 is obtained.

  When the processing as described above is further advanced, the second and subsequent FFT result values of the stream data SD1 to SD3 are sequentially output from the selector 12c of the butterfly computation unit 12-3 at the last stage.

  As described above, in the FFT circuit 10 according to the present embodiment, the multiplexer 11 outputs one partial data of one stream data in a predetermined stream data order every unit time. Then, a delay unit 13-1 provided corresponding to the first stage butterfly calculation unit 12-1 inputs the partial data in the order of the stream data, delays it, and supplies it to the butterfly calculation unit 12-1. The butterfly computation unit 12-1 performs computation using the partial data output from the multiplexer 11 and the delayed partial data at that time.

  As a result, a plurality of stream data can be subjected to FFT processing for each partial data by one pipeline-type FFT circuit 10, and FFT can be performed on the plurality of stream data by a small circuit.

  In the above description, the FFT circuit 10 to which the SDF (Single Path-Delay Feedback) method is applied has been described. However, the present invention is not limited to this method. A pipeline-type FFT circuit that performs the same processing can also be realized for the MDC (Multi-Path Delay Commutator) method or other methods.

In the above description, the FFT circuit 10 that performs FFT with a radix of 2 has been described. However, the radix is not limited to 2.
The FFT circuit that realizes the processing of the present embodiment as described above includes a multiplexer that receives a plurality of stream data and outputs partial data of each stream data in a predetermined stream data order for each unit time. The first stage butterfly calculation unit inputs the partial data output from the multiplexer as one input data. Then, a delay unit provided corresponding to the first stage butterfly operation unit inputs the partial data output from the multiplexer in the order of the stream data, and outputs the delayed data as the other input data of the first stage butterfly operation unit.

  Also, the delay time of the delay unit is such that the number of streams and partial data are such that the delay unit outputs partial data of the same stream data as partial data included in one of the data input to the butterfly operation unit. It is set according to the number. For example, as shown in FIG. 3, when the partial data x4 of the stream data SD1 is input to the butterfly operation unit 12-1, the delay is performed so that the partial data x0 of the same stream data SD1 is output from the delay unit 13-1. The time is set.

  Further, the FFT circuit that realizes the processing of the present embodiment has a multiplication circuit that receives a clock signal having a period that is multiple times the number of streams per unit time and generates a multiplied clock signal that is obtained by multiplying the clock signal frequency by the number of data strings . The FFT circuit also has a counter that generates a selection signal for the multiplexer that is updated at the cycle of the multiplied clock signal, and generates a control signal that is obtained by dividing the multiplied clock signal by the number of times the number of stream data. Furthermore, the FFT circuit includes a twiddle factor generation unit that updates the twiddle factor at a timing according to the control signal.

By providing each element as described above, not only the FFT circuit 10 described above but also an FFT circuit that can obtain the same effect can be realized.
The above merely shows the principle of the present invention. Further, many variations and modifications are possible for those skilled in the art. The present invention is not limited to the exact configuration and application shown and described above, but all corresponding variations and equivalents are considered as the scope of the invention by the appended claims and their equivalents. .

DESCRIPTION OF SYMBOLS 10 FFT circuit 11 Multiplexer 12-1 to 12-3 Butterfly operation part 12a Operation part 12b, 12c Selector 13-1 to 13-3 Delay part 13a Shift register 14-1, 14-2 Multiplication part 15-1, 15-2 Rotation factor generator 16 Multiplier circuit 17 Counter 18 Controller CLK Clock signal line IN1-IN3 Input signal line OUT Output signal line x0, y0, z0 Partial data

However, the conventional method for processing stream data of a plurality of channels has a problem that the circuit scale becomes large because a pipeline type FFT circuit is provided for each channel.

The delay unit 13-1 provided corresponding to the first stage butterfly operation unit 12-1 has a shift register 13a, and shifts the data taken in synchronization with the multiplied clock signal generated by the multiplication circuit 16. after a delay during content at any given time, and outputs. The delay units 13-2 and 13-3 have similar shift registers, but are not shown in FIG.

The counter 17 generates a selection signal for the multiplexer 11 that is updated at the cycle of the multiplied clock signal, and sends a control signal (hereinafter referred to as an enable signal) obtained by dividing the multiplied clock signal by the number of stream data to the control unit 18. Output function. When the number of stream data is 3, the counter 17 is a 3- digit binary counter that counts the rising or falling edge of the multiplied clock signal and the count value is 2 ((10) in binary notation). , “1” is output to the control unit 18.

When the multiplied clock signal rises next, the same processing is performed, the partial data z0 is taken into the shift register 13a, and the shift register 13a is in the state shown in FIG. In addition, since the multiplied clock signal is input while the enable signal is “1”, the control unit 18 counts and the bit Q0 becomes “1”. However, the bits Q1 and Q2 remain “0”. Therefore, in butterfly operation unit 12-1, the selector 12b selects the partial data x1 to multiplexer 11 outputs, and outputs to the delay unit 13 -1.

The twiddle factor generator 15-2 outputs “1” when the input bits Q 1 and Q 0 are (10). Therefore, the multiplication unit 14-2 outputs (x0 + x4) + (x2 + x6). In the butterfly operation unit 12-3 in the next stage, the selector 12b outputs (x0 + x4) + (x2 + x6) to the delay unit 13-3 because the bit Q0 input as the selection signal is “0”.

In addition, the FFT circuit that realizes the processing of the present embodiment includes a multiplication circuit that receives a clock signal having a period that is multiple times the number of stream data per unit time and generates a multiplied clock signal that is obtained by multiplying the frequency of the clock signal by the number of stream data. Have. Further, the FFT circuit has a counter that generates a selection signal for a multiplexer that is updated at a cycle of the multiplied clock signal and generates a control signal obtained by dividing the multiplied clock signal by the number of stream data. Furthermore, the FFT circuit includes a twiddle factor generation unit that updates the twiddle factor at a timing according to the control signal.

Claims (3)

A multiplexer that receives a plurality of data strings parallel on the time axis and outputs partial data of each data string in a predetermined data string order for each unit time;
A plurality of delay units for delaying and outputting input data; and
A plurality of stages are provided corresponding to the plurality of delay units, the output data of the corresponding delay unit is input as first input data, the sum and difference with the second input data are calculated, and one of the calculation results or A butterfly operation unit that outputs the second input data to the corresponding delay unit;
A multiplication unit that multiplies the other computation result of the butterfly computation unit or the output data of the corresponding delay unit and a twiddle factor and outputs the result as the second input data of the butterfly computation unit in the subsequent stage; ,
The butterfly operation unit in the first stage inputs the partial data output from the multiplexer as the second input data,
Among the plurality of delay units, a delay unit provided corresponding to the first stage butterfly operation unit inputs the partial data output from the multiplexer in the order of the data string, and delays the first stage butterfly operation unit. A fast Fourier transform circuit that outputs the first input data of   In the plurality of delay units, the first input data including partial data of the same data string as the partial data included in the second input data is input to the butterfly calculation unit together with the second input data. The fast Fourier transform circuit according to claim 1, wherein a delay time is set according to the number of data strings and the number of partial data. A multiplication circuit that receives a clock signal having a period that is the number of data strings times the unit time, and that generates a multiplied clock signal in which the frequency of the clock signal is multiplied by the number of data strings;
A counter that generates a selection signal of the multiplexer to be updated at a cycle of the multiplied clock signal, and generates a control signal obtained by dividing the multiplied clock signal by the number of times of the data string;
A twiddle factor generator that updates the twiddle factor at a timing according to the control signal;
The fast Fourier transform circuit according to claim 1 or 2, further comprising:

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