Complex number multiplication circuit

Abstract: A complex number calculation circuit for directly multiplying a complex number of an analog signal by a digital complex number as a multiplier. A capacitive coupling is used with a plurality of parallel capacitances corresponding to weights of bits of real and imaginary parts of the multiplier. Sign of the multiplier is represented by selection of outputs paths. A complex number calculation circuit for calculating approximated absolute value suitable for an analog architecture. Inverter circuits are used for linear inversion of analog values, and capacitive couplings are use for weighted addition. Analog maximum and minimum circuits with parallel MOSs are used for maximum and minimum calculation.

Description: This invention relates to complex number calculation circuits according to the preamble part of claims 1 and 2, respectively. Such complex number calculation circuits are described in US-A-4,354,249. This reference discloses a processor unit for multiplying mathematical quantities, including at least one complex multiplier. The complex multiplier includes four real multiplier circuits, each of which has two inputs and one output. The input lead carrying the real portion of the components of vectors X and Y is connected to both inputs of a first multiplier circuit and one input of a second and a third multiplier circuit. The input lead carrying the imaginary portion of the components of the vectors X and Y is connected to both inputs of a fourth multiplying circuit and one input of the second and the third multiplying circuits. In order to obtain a dot product from the complex multiplier, the output from the first and fourth multiplying circuits are applied to a combining circuit and the output of the second and third multiplying circuits are applied to another combining circuit. US-A-5,416,370 discloses a multiplication circuit. The multiplication circuit comprises a plurality of switching circuits. Each switching circuit receives one bit of a digital multiplier and an analog signal. If a bit is zero, the corresponding switching circuit outputs zero. On the other hand, if this bit is one, the switching circuit outputs the analog voltage. The output of each switching circuit is weighted by a corresponding capacitor wherein the capacity of each capacitor corresponds to the significance of the corresponding bit. It is the object of this invention to provide a complex number calculation circuit which is adapted to multiply analog voltages by a digital complex multiplier. The analog voltages represent the absolute value of a real part and an imaginary part of a complex number. This object is achieved by a complex number calculation circuit according to claim 1 or claim 2. In the following preferred embodiments of this invention are described referring to the accompanying drawings. Fig. 1 shows the first embodiment of a complex number multiplication circuit according to the present invention. Fig. 2 shows a circuit of a selector of the embodiment. Fig. 3 shows a circuit of the second embodiment. Fig. 4 shows a multiplication circuit used in the embodiment. Fig. 5 shows an inverter circuit of the embodiment. Hereinafter the first embodiment of the complex number calculation circuit according to the present invention is described with reference to the attached drawings. In Fig. 1, a complex number multiplication circuit includes the first multiplication circuit MUL1 and the fourth multiplication circuit MUL4 to both of which the real part x of a complex number (x+iy) is input, and the second multiplication circuit MUL2 and the third multiplication circuit MUL3 to both of which the imaginary part y of a complex number (x+iy) is input. The absolute value | a | of the real part of the second complex number (a+ib) is input to the first and the third multiplexers, and the absolute value | b | of the imaginary part is input to the second and the fourth multipliers. x and y are input as an analog voltage, and | a | and | b | are input as a digital signal. In the multiplication circuits MUL1 to MUL4, the operations below are performed. The First Multiplier MUL1 : - | a | x The Second Multiplier MUL2: - | b | y The Third Multiplier MUL3 : - | a | y The Fourth Multiplier MUL4 : - | b | x The products of (x-iy) and (a+ib), that is formula (5) can be obtained by combining them. (x+iy)(a+ib)=(ax-by)+i(bx+ay) As in Fig. 4, the first multiplication circuit MUL1 includes a plural number of multiplexers MUX40 to MUX47, to which an analog input x is commonly input. There are input to the multiplexers a reference voltage Vref corresponding to an analog input 0 and each bit of a digital signal of | a | of the absolute value of the real part of the second complex number. Assuming that the each bit of | a | to be Ba0, Ba1, Ba2, Ba3, Ba4, Ba5, Ba6, and Ba7 from the lowest, they are successively input to MUX40 to MUX47. In Fig. 4, the whole of the digital signal is shown by Ba. The multiplexers MUX40 to MUX47 output x when Ba0 to Ba7 corresponding to them are 1, and they output Vref when Ba0 to Ba7 are 0. A capacitive coupling Cp4 constructed by capacitances C40 to C47 it connected to the outputs of MUX40 to MUX47. Each capacitance is connected to the corresponding multiplexer, and their outputs are integrated. An output of the capacitive coupling Cp4 is input to an inverting amplifier including an inverter circuit INV4 and a feedback capacitance C48, then, a multiplication result is generated as an output of an inverting amplifier Vout4 The ratio of capacitances C40 to C47 and C48 is C40:C41:C42:C43:C44:C45:C46:C47:C48=1:2:4:8:16:32:64:128:255 Assuming the supply voltage of INV4 is Vdd, Vout 4 can be expressed as in formula (7). An analog voltage X corresponds to minus value when 0 ≦ X < Vref, X=0 when X=Vref, and plus voltage when Vref < X ≦ Vdd. INV4 is a circuit of high open gain with preventing an unstable oscillation by a grounded capacitance and a balancing resistance. It has good linearity regardless the load in the following stages. This circuit is described in detail in JP 7-94957. As above, the multiplication circuit directly multiplies the complex number given as an analog voltage and generates an analog output. The structures of other multipliers MUL2 to MUL4 are the same as MUL1, the description is omitted. Outputs of each multiplier MUL1 to MUL4 are input to selector SEL1 to SEL4 each of which has an input and two outputs, then the path of output is selected according to the polarity of the real part and the imaginary part of the second complex number as shown in Fig. 1. The code bit "sa" of the real part a is input to the selectors SEL1 and SEL3, and the code bit "sb" of the imaginary part b is input to the selectors SEL2 and SEL4. The outputs of SEL1 and SEL2 are connected to capacitive couplings Cp11 or Cp12. The outputs to Cp11 and Cp12 are defined to be the first line and the second line, respectively. The outputs of SEL3 and SEL4 are connected to the capacitive coupling Cp21 or Cp22. The outputs to Cp21 and Cp22 are defined to be the first and the second lines, respectively. The first and the second paths (lines) are selected according to the condition in TABLE 1. CONDITION OF SELECTING OUTPUT OF SELECTOR LINE SEL1 SEL2 SEL3 SEL4 The First Line a < 0 b ≧ 0 a < 0 b < 0 The Second Line a ≧ 0 b < 0 a ≧ 0 b ≧ 0 The capacitive coupling Cp11 is constructed by connecting capacitances C11 and C12 in parallel. It adds the outputs of SEL1 and SEL2. The output of Cpl I is connected to an inverted amplifier INV11 similar to INV4, and an input and output of INV11 are connected by a capacitance C13. The capacitance ratio of C11, C12 and C13 is 1:1:2. Even when an input is substantially the same as Vdd, the output of INV11 is prevented to exceed Vdd. Assuming the output voltage of the first system of SEL1 and SEL2 are V11 and V21, respectively, and the output of INV11 to be V111, the equation in formula (8) is true. V 111= Vdd - C 11 V 11+ C 12 V 21 C 13 = Vdd - 1 2 ( V 11- V 21) The capacitive coupling Cp12 is structured by connecting capacitances C14, C15 and C16 in parallel. An inverting amplifier INV12 and a feedback capacitance C17 are connected to the output, the ratio of the capacity of C14:C15:C16:C17=1:2:1:4. Even when an input is substantially the same as Vdd, the output of the INV12 is prevented from exceeding the Vdd. The capacity of C15 is the twice as much as C14 and C16 so as to balance with the previous stage. Assuming the output of the second system of SEL1 and SEL2 are V12 and V22, V112 of the output of INV12 is as in the formula (9). V 112= Vdd - C 14 V 12+ C 15 V 111+ C 16 V 22 C 17 = Vdd - 1 4 ( V 12+2 V 111+ V 22) When formula (9) is substituted for formula (8), formula (10) can be obtained. V 112= 1 2 Vdd + 1 4 ( V 11+ V 21- V 12- V 22) From TABLE 1, V11, V12, V21 and V22 have the values below. V11 V12 V21 V22 a ≧ 0 Vref=0 -ax ------ ------ a < 0 ax Vref=0 ------ ------ b ≧ 0 ------ ------ -by Vref=0 b < 0 ------ ------ Vref=0 by When the offset and the magnification are ignored, the output V112 can be expressed by formula (11) regardless the polarities of a and b. V112=ax-by The formula (11) corresponds to the real part of the multiplication result in formula (5). The capacitive coupling Cp21 is structured by connecting capacitances C21 and C22 in parallel. It adds the outputs of SEL3 and SEL4. The input and output of INV21 is connected by a feedback capacitance C23. The capacity ratio of C21, C22 and C23 is 1:1:2. Even when x and y are the voltage substantially the same as Vdd, the output of INV21 is prevented from exceeding Vdd. Assuming the output voltage of the first lines of SEL3 and SEL4 to be V31 and V41, respectively, and assuming an output of INV121 to be V121, the equation below is true. V 121= Vdd - C 21 V 31+ C 22 V 41 C 23 = Vdd - 1 2 ( V 31+ V 41) Capacitive coupling Cp22 is structured by connecting capacitances C24, C25 and C26 in parallel. An inverting amplifier INV22 and a feedback capacitance C27 are connected to its output. The capacitance ratio of C24, C25, C26 and C27 is 1:2:1:4. Even when an input is substantially the same voltage, an output of INV22 is prevented from exceeding Vdd. The capacity of C25 is twice as large as C24 and C26 so as to balance with the previous stage. Assuming the output of two lines of SEL3 and SEL4 to be V32 and V42, respectively, V122 of the output of INV22 can be obtained by the formula (13). V 122= Vdd - C 24 V 32+ C 25 V 121+ C 26 V 42 C 27 = Vdd - 1 4 ( V 32+2 V 121+ V 42) Substituting the formula (12) for the formula (13), formula (14) can be obtained. V 122 = 1 2 Vdd + 1 4 ( V 31+ V 41- V 32- V 42) From TABLE 1, V31, V32, V41 and V42 have values below. V31 V32 V41 V42 a ≧ 0 Vref=0 ay ------ ------ a < 0 -ay Vref=0 ------ ------ b ≧ 0 ------ ------ Vref=0 bx b < 0 ------ ------ -bx Vref=0 When the offset and the magnification is ignored, the output V122 can be expressed by formula (15) regardless the polarity of a and b. V112=bx+ay The formula (15) corresponds to the imaginary part of the formula (5). In Fig. 2, the selector SEL1 includes a pair of multiplexers MUX21 and MUX22. An input voltage Vin2 (an output of MUL1 in Fig. 1) and the reference voltage Vref are input to the multiplexers. Each multiplexer selectively outputs Vin2 or the reference voltage Vref, and MUX21 and MUX22 are controlled by a control signal S so as to generate outputs different from each other. The control signal S is input to MUX22, as well as input to MUX21 through an inverter INV2. That is, by control signals of opposite logic are input to MUX22. Consequently, MUX21 and MUX22 output different signals. The multiplexers are structured by well-known circuits such as controlling a pair of MOS switches by a control signal of opposite logic. As above, the complex number multiplying circuit can directly multiply a complex number as an analog signal and as a digital signal, and it generates an output in the form of an analog voltage. Therefore, a circuit for AID and D/A is not necessary. It is appropriate for an analog architecture. Fig 3 shows the second embodiment of the present invention. In the figure, the same or substantially the same part as in the first embodiment is designated by the same references. In the second embodiment, the multiplication circuits MUL3, MUL4 and addition portions of the circuits on the stages following to SEL3 and SEL4 in the first embodiment are omitted and the circuit is simplified. The complex number given by digital signals is separated into the real part and the imaginary part and processed by the individual timing. That is, the real part and the imaginary part can be operated by switching the path in the circuit, which is processed within 1 operation clock. In Fig. 3, the complex multiplier includes the first and the second multiplication circuits MUL1 and MUL2 similar to the first embodiment. Outputs of MUL1 and MUL2 are input to selectors SEL1 and SEL2, respectively. With respect to the outputs of SEL1 and SEL2, the output of the first line of SEL1 and SEL2 is input to the capacitive coupling Cp11, otherwise, the output of the second line is input to the capacitive coupling Cp12. An output of Cp11 is input to the inverter INV11. The output of INV11 is input to Cp12, as well as connected to its input through a feedback capacitance C13. An output of the Cp12 is input to an INV12 to which a feedback capacitance C17 is connected. A digital multiplier is input to the multiplication circuit MUL1 through multiplexer MUX31, and it is input to the multiplication circuit MUL2 through multiplexer MUX32. Absolute values | a | and | b | are input to MUX31 and MUX32. They output one of the multipliers according to a control signal Ctr13. Ctr13 is input to the MUX31, as well as input to the MUX32 through an inverter INV3. Control signals ssl and ss2 are also input to SEL1 and SEL2 in order to select the first line or the second line. For example, when the real part (ax-by) of the multiplication result is generated, the multipliers of MUL1 and MUL2 are | a | and | b |, respectively. The signal ssl defines sign of the multiplier of MUL1 ("a", in this case), and signal ss2 determined according to the selection of the multiplier of MUL2 ("b", in this case) and the sign of selected multiplier b. -ax is generated on the second line and Vref=0 is generated on the first line when a is designated by ssl as plus or 0. ax is generated on the first line and 0 is generated on the second line when a is designated by ss1 as minus. -by and 0 are generated on the first and second line, respectively, when b is designated by ss2 as plus or 0. "by" and 0 are generated on the second line and the first line, respectively, when b is designated by ss2 as minus. When the imaginary part (bx+ay) of the multiplication result is generated, the multipliers of MUL1 and MUL2 are | b | and | a |, respectively, ss1 is a signal of the multiplier of MUL1 ("b", in this case), and ss2 is a signal determined by the selection of the multiplier of MUL2 ("b", in this case) and the polarity of selected multiplier a. -bx is generated on the second line and Vref=0 is generated on the first line when b is designated by ss1 as plus or 0. bx is generated on the first line and 0 is generated on the second line when b is designated by ss1 as minus, -ay and 0 are generated on the second and first line, respectively, when a is designated by ss2 as plus or 0. "ay" and 0 are generated on the first line and the second, respectively, when a is designated by ss2 as minus. The above settlements are shown in TABLE 4. Selection of Multiplier Line a ≧ 0 a < 0 b ≧ 0 b < 0 Multiplier of MUL1 is "a" The First Line The Second Line 0 -ax ax 0 -by 0 0 by Multiplier of MUL1 is "b" The First Line The Second Line 0 -ay ay 0 0 -bx bx 0 Since the number of addition portions is reduced to one by substitution of a plurality of multipliers. It contributes to the reduce of electric power consumption. As shown in Fig. 5, in an inverter circuit INV11, odd number of MOS inverters 11, 12 and 13 are serially connected and INV11 has a high gain as a product of gain of each inverter. In the inverter circuit INV11 (INV12, INV21 and INV22 have the same structure.), a capacitance C2 is connected to the end of the output as a low-pass filter, and a balancing resistance including resistances R21 and R22 is connected to an output of the second stage inverter 12. One terminal of R21 is connected to 12 and another terminal is connected to the supply voltage Vdd. One terminal of R22 is connected to 12 and another terminal is grounded. The balancing resistance loweres a gain of the inverter circuit, and the capacitance cancel a component of a high frequency. Consequently, unusable oscillation is prevented, which may occur in the feedback system of the feedback capacitance. As above, in a complex number multiplication circuit according to the present invention, it is used a capacitive coupling in which a plurality of capacitances corresponding to weights of bits of a digital multiplier are arranged in parallel, and a digital multiplier is multiplied to the complex number given by an analog voltage. The path is switched according to the polarities of real part or imaginary part and one or two inverted amplifiers are passed, as well as the multiplication results are added by the capacitive coupling. It is possible to directly multiply a complex number given by an analog signal and the operation results can be obtained as an analog voltage by the complex number multiplication circuit according to the present invention.

Claims: A complex number calculation circuit (Fig. 1) comprising: i) a first multiplying circuit (MUL1) to which a first signal corresponding to a real part (x) of a first complex number and a second signal corresponding to a real part of a second complex number (|a|) are input; ii) a second multiplying circuit (MUL2) to which a third signal corresponding to a imaginary part (y) of said first complex number and a fourth signal corresponding to an imaginary part of said second complex number (|b|) are input; iii) a third multiplying circuit (MUL3) to which said third signal and said second signal are input; iv) a fourth multiplying circuit (MUL4) to which said first signal and said fourth signal are input; v) a first addition and subtraction portion (Cp11, C13, INV11, Cp12, C17, INV12) coupled to an output of said first multiplying circuit and an output of said second multiplying circuit for yielding the real part of the product of said first and second complex numbers; vi) a second addition and subtraction portion (Cp21, C23, INV21, Cp22, C27, INV22) coupled to an output of said third multiplying circuit and an output of said fourth multiplying circuit for yielding the imaginary part of the product of said first and second complex numbers; characterized in that said real and imaginary parts of said first complex number are provided as analog voltages, whereas the real and imaginary parts of said second complex number are provided as digital signals; each multiplying circuit comprises: a) a capacitive coupling to which said signals are input and in which capacitances corresponding to a weight of each bit of said input digital signal are parallelly connected; b) a plurality of first multiplexers (MUX40 ... MUX47) for alternatively connecting said input analog signal (x, y) or a reference voltage (Vref) to each said capacitance (C40 ... C47) according to a value of each bit of said digital signal (Ba) in said capacitive coupling (Cp4); and c) a inverting amplifier (INV4) with linear relationship between an input and an output, to which an output of said capacitive coupling (Cp4) is input; each addition and subtraction portion comprises: a) a first capacitive coupling (Cp11, Cp21); b) a first inverting amplifier (INV11, INV21) with linear relationship berween an input and an output, to which an output of said first capacitive coupling is input; c) a second capacitive coupling (Cp12, Cp22) to which an output (V111, V121) of said first inverting amplifier (INV11, INV21) is input; and d) a second inverting amplifier (INV12, INV22) with linear relationship between an input and output, to which an output of said second capacitive coupling is connected; said complex number calculation circuit further comprises: vii) a first selector (SEL1) connected to an output of said first multiplying circuit (MUL1), to which a first control signal (sa) is input for introducing said output of said first multiplying circuit (MUL1) to a first output (V11) connected to said first capacitive coupling (Cp11) of said first addition and subtraction portion or a second output (V12) connected to said second capacitive coupling (Cp12) of said first addition and subtraction portion in response to a polarity of said real part (a) of said second complex number. viii) a second selector (SEL2) connected to an output of said second multiplying circuit (MUL2), to which a second control signal (sb) is input for introducing said output of said second multiplying circuit (MUL2) to a first output (V21) connected to said first capacitive coupling (Cp11) of said first addition and subtraction portion or a second output (V22) connected to said second capacitive coupling (Cp12) of said first addition and subtraction portion in response to a polarity of said imaginary part (b) of said second complex number. ix) a third selector (SEL3) connected to an output of said third multiplying circuit (MUL3), to which a first control signal (sa) is input for introducing said output of said third multiplying circuit (MUL3) to a first output (V31) connected to said first capacitive coupling (Cp21) of said second addition and subtraction portion or a second output (V32) connected to said second capacitive coupling (Cp22) of said second addition and subtraction portion in response to a polarity of said real part (a) of said second complex number. x) a fourth selector (SEL4) connected to an output of said fourth multiplying circuit (MUL4), to which a second control signal (sb) is input for introducing said output of said fourth multiplying circuit (MUL4) to a first output (V41) connected to said first capacitive coupling (Cp21) of second first addition and subtraction portion or a second output (V42) connected to said second capacitive coupling (Cp22) of said second addition and subtraction portion in response to a polarity of said imaginary part (b) of said second complex number. A complex number calculation circuit (Fig. 3) comprising: i) a first multiplying circuit (MUL1) to which a first signal corresponding to a real part (x) of a first complex number and and a second signal are input; ii) a second multiplying circuit (MUL2) to which a third signal corresponding to a imaginary part (y) of said first complex number and a fourth signal are input; iii) an addition and subtraction portion (Cp11, C13, INV11, Cp12, C17, INV12) coupled to an output of said first multiplying circuit and an output of said second multiplying circuit for yielding either the real part or the imaginary part of the product of said first and a second complex number; characterized in that said real and imaginary parts of said first complex number are provided as analog voltages, whereas said second and fourth signals are provided as digital signals; each multiplying circuit comprises: a) a capacitive coupling to which said signals are input and in which capacitances corresponding to a weight of each bit of said input digital signal are parallelly connected; b) a plurality of first multiplexers (MUX40 ... MUX47) for alternatively connecting said input analog signal (x, y) or a reference voltage (Vref) to each said capacitance (C40 ... C47) according to a value of each bit of said digital signal (Ba) in said capacitive coupling (Cp4); and c) a inverting amplifier (INV4) with linear relationship between an input and an output, to which an output of said capacitive coupling (Cp4) is input; said addition and subtraction portion comprises: a) a first capacitive coupling (Cp11); b) a first inverting amplifier (INV11) with linear relationship berween an input and an output, to which an output of said first capacitive coupling is input; c) a second capacitive coupling (Cp12) to which an output (V111) of said first inverting amplifier (INV11) is input; and d) a second inverting amplifier (INV12) with linear relationship between an input and output, to which an output of said second capacitive coupling is connected; said complex number calculation circuit further comprises: iv) a first multiplexer (MUX31) to which a fifth digital signal corresponding to an absolute value of a real part (|a|) of said second complex number and a sixth digital signal corresponding to an absolute value of an imaginary part (|b|) of said second complex number and a first control signal (Crtl3) for selecting a first state or a second state are input, in said first state said fifth signal being output as said second signal, in said second state said sixth signal being output as said second signal, v) a second multiplexer (MUX32, INV3) to which said fifth and sixth signals and said first control signal (Crtl3) for selecting a first or a second state are input, in said first state said sixth signal being output as said fourth signal, in said second state said fifth signal being output as said fourth signal; vi) a first selector (SEL1) connected to an output of said first multiplying circuit (MUL1), to which a second control signal (ss1) is input for introducing said output of said first multiplying circuit (MUL1) to a first output connected to said first capacitive coupling (Cp11) of said addition and subtraction portion if said real part or said imaginary part of said second complex number is negative or to a second output connected to said second capacitive coupling (Cp12) of said addition and subtraction portion if said real part or said imaginary part of said second complex number is positive; vii) a second selector (SEL2) connected to an output of said second multiplying circuit (MUL2), to which a third control signal (ss2) corresponding to said polarity of said real part or said imaginary part of said second complex number and corresponding to said first or second state of said first and second multiplexers is input, said output of said second multiplying circuit being introduced to a first output connected to said first capacitive coupling (Cp11) if said first and second multipexers are in said first state, and said imaginary part of said second complex number is positive, or if said multiplexers are in said second state and said real part of said second complex number is negative; or a second output connected to said second capacitive coupling (Cp12) if said first and second multiplexers are in said first state and said imaginary part of said second complex number is negative, or if said multiplexers are in said second state and said real part of said second complex number is positive, wherein said first and second state of said first and second multiplexers are obtained by switching said first control signal in one clock of an operation.

Inventors: SHOU GUOLIANG, TAKATORI SUNAO, YAMAMOTO MAKOTO, ZHOU CHANGMING, SHOU GUOLIANG,, TAKATORI SUNAO,, YAMAMOTO MAKOTO,, ZHOU CHANGMING,
Applicants: SHARP KK, YOZAN INC, SHARP KABUSHIKI KAISHA, YOZAN INC.
Application year: 1996
Main classification: G06J1
IPC codes: G06J1, G06G7