Cordic complex multiplier

• US 4,896,287 A
• Filed: 05/31/1988
• Issued: 01/23/1990
• Est. Priority Date: 05/31/1988
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Engeler, William E., O'Donnell, Matthew
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): Mai, Tan V.
• Application Number:
  US07/200,491
• Time in Patent Office: 602 Days
• Field of Search: 364/754, 364/757, 364/730
• US Class Current: 708/622
• CPC Class Codes: G06F 7/4812 Complex multiplication
• CPC Class Codes: G06F 7/4818 using coordinate rotation digital computer [CORDIC]
• CPC Class Codes: G06F 7/5446 using crossaddition algorithms, e.g. CORDIC
• CPC Class Codes: H03C 3/40 using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated

Abstract

A CORDIC (COordinate Rotation DIgital Computer) subsystem for multiplication of two complex digital numbers B and C, where one number is the sum of real and imaginary data portions, expressed in rectangular form (say C_r or C_I), and the other number can be expressed in the rectangular form or can be represented by magnitude data, expressed in polar form (say, |B|, φ). An N-stage CORDIC portion of either recursive or pipeline sequential form, but devoid of multipliers, is used to rotate the I and Q terms of the first number through a phase angle φ of the polar-form multiplier number of the equivalent, taken from the rectangular form. The final computed data are the real and imaginary parts of the product.

Claims

1. A recursive CORDIC rotator, comprising:

means for receiving digital data words representing each of the real C_R part and the imaginary C_I part of a first complex number C;

a first portion including means for rotating each one of the first complex number real C_R part and imaginary C_I part by a first angular increment α

₁ of a selected one of +90° and

-90°

to form an associated one of digital data words I and Q;

a recursion portion including means for rotationally modifying each of the I and Q digital data words, received from the first portion, recursively through each selected one of positive and negative incremental angles α

₁, for 2≦

i≦

N, where N is a positive integer greater than 2, and each incremental angle α

_i not only less than angle α

₁ but also greater than a next incremental angle α

_i+1 ;

means for receiving a digital data word representing an angular rotation φ

portion of a second complex number B, expressed in amplitude/rotation angle form, and for controlling the signs of the angle α

₁ in the first portion and all of the incremental angles α

₁ in the recursion portion to successively approximate the second complex number rotation angle φ

; and

means for providing the first and second parts, after rotational modification through all N angles, respectively as a rotated imaginary-part output digital data word A_I substantially equal to (B_R C_I -B_I C_R), where B_R and B_I are respective real and imaginary parts of the second complex number B, and a rotated real-part output digital data word A_R substantially equal to (B_R C_R +B_I C_I).

2. The rotator of claim 1, wherein the first increment α

₁ rotating means includes means for selecting one of the same sign and the reversed sign for each respective one of the first complex number real and imaginary parts, responsive to a respective one of first and second sign-control signals from said sign controlling means.

3. The rotator of claim 2, wherein each incremental angle α

_i =tan^-1 (2^-n), for n=i-2.

4. The rotator of claim 3, wherein i is less than 8.

5. The rotator of claim 3, wherein the recursion portion rotating means includes:

first means for accumulating the I digital data word from the first portion and each sequential one of (N-1) first sequentially-shifted digital data words;

second means for accumulating the Q digital data word from the first portion and each sequential one of (N-1) second sequentially-shifted digital data words;

first sign-select means for selectively reversing, responsive to a first sign-select means sign-control signal from said sign-controlling means, the sign of the digital data word then provided by said first accumulator means;

second sign-select means for selectively reversing, responsive to a second sign-select means sign-control signal from said sign-controlling means, the sign of the digital data word then provided by said second accumulator means;

first means for shifting the bits of the digital data word from said first sign-select means by one bit in a predetermined direction for each occurrence of a first shifting means control signal from said sign-controlling means;

second means for shifting the bits of the digital data word from said second sign-select means by one bit in a predetermined direction for each occurrence of a second shifting means control signal from said sign-controlling means;

first adder means for adding the digital data words from the first accumulator means and the second shifting means to provide each sequential one of the (N-1) first sequentially-shifted digital data words both to the first accumulator means and as the A_I output digital data word; and

second adder means for adding the digital data words from the second accumulator means and the first shifting means to provide each sequential one of the (N-1) second sequentially-shifted digital data words both to the second accumulator means and as the A_R output digital data word;

said sign-control means having additional outputs at which said first and second sign-control means and first and second shifting means sign-control signals are all provided for each of the (N-1) recursions, responsive to the received rotation angle φ

data.

6. A sequential CORDIC rotator, comprising:

means for receiving digital data words representing each of the real I and imaginary Q parts of a first complex number;

a first portion including stage means for separately rotating each one of the first and second complex number real and imaginary parts by a first angular increment α

₁ of a selected one of +90° and

-90°

;

a second portion including a plurality (N-1) of stage means, where N is a positive integer greater than 2, each for rotationally modifying a pair of input real and imaginary part digital data words through one selected one of a positive and negative incremental angles α

_i, for 2≦

i≦

N, with each i-th stage means incremental angle α

_i not only less than angle α

₁ but also greater than a next stage incremental angle α

_i+1, and with the pair of input digital data words to the second portion first stage means being received from the first portion and the pair of input digital data words for any other stage means of the second portion being received from an immediately-previous second portion stage means;

means for receiving a digital data word representing an angular rotation φ

portion of a second complex number expressed in amplitude/rotation-angle form, and controlling the signs of the angle α

₁ in the first portion and all of the incremental angles α

₁ in the plurality of stage means to approximate the second complex number rotation angle φ

; and

means for providing the first and second parts, after rotational modification through all N angles, respectively as a rotated imaginary-part output digital data word and a rotated real-part output digital data word.

7. The rotator of claim 6, wherein the first increment α

₁ rotating means includes means for selecting one of the same sign and the reversed sign for the selected one of the first and second complex number real and imaginary parts, responsive to a first-increment sign-control signal from said sign controlling means.

8. The rotator of claim 7, wherein each incremental angle α

_i =tan^-1 (2^-n), for n=i-2.

9. The rotator of claim 8, wherein i is less than 8.

10. The rotator of claim 8, wherein each stage means includes:

means for receiving both a real part digital data word and an imaginary part digital data word input to that stage means;

first means for shifting the bits of the real part input digital data word means by n bits in a predetermined direction;

second means for shifting the bits of the imaginary part input digital data word by n bits in the predetermined direction;

first sign-select means for selectively reversing, responsive to a first sign-select means control signal from said sign-controlling means, the sign of the shifted digital data word from the first shifting means;

second sign-select means for selectively reversing, responsive to a second sign-select means control signal from said sign-controlling means, the sign of the shifted digital data word from the second shifting means;

first adder means for adding the real part input digital data word and the digital data word from the second sign-select means to provide a real part output digital data word from that stage means; and

a second adder means for adding the imaginary part input digital data word and the digital data word from the first sign-select means to provide an imaginary part output digital data word from that stage means;

said sign-control means having additional outputs at which are provided, responsive to the received rotation angle φ

data,, all first and second sign-control means control signals for all (N-1) stage means.

11. Apparatus for providing output digital data which is the produce of a first complex number C, represented as a real-part digital data word C_R and an imaginary-part digital data word C_I, and a second complex number B, represented as a magnitude |B| digital data word and a phase angle φ

digital data word comprising;

input means, receiving at least the first complex number real-part digital data word C_R and the imaginary-part digital data word C_I, for providing an input real-part digital data word I and an input imaginary-part digital data word O;

CORDIC means for rotationally modifying respectively the input real-part digital data word I and the input imaginary part digital data word Q responsive to the phase angle φ

digital data word to respectively obtain an output digital data word Q'"'"' and an output digital data word I'"'"'; and

output means receiving the respective output Q'"'"' and I'"'"' digital data words for respectively providing an imaginary part A_I and a real-part A_R of a digital data word for an output complex number A proportional to the product of B and C.

12. The apparatus of claim 11, wherein the CORDIC means is a recursive CORDIC rotator.

13. The apparatus of claim 12, wherein the output means further comprises:

means receiving the second complex number magnitude |B| digital data word; and

means for scalar multiplying each respective one of the real-part digital data word I'"'"' and the imaginary-part digital data word Q'"'"' by the magnitude |B| digital data word to obtain the respective real-part A_R and imaginary-part A_I digital data words.

14. The apparatus of claim 11, wherein the CORDIC means is a sequential CORDIC rotator.

15. The apparatus of claim 14, wherein the output means further comprises means receiving the second complex number magnitude |B| digital data word;

and means for scalar multiplying each respective one of the real-part digital data word I'"'"' and the imaginary-part digital data word Q'"'"' by the magnitude |B| digital data word to obtain the respective real-part A_R and imaginary-part A_I digital data words.

16. Apparatus for providing output digital data which is the product of a first complex number, represented as a real-part digital data word I₁, and an imaginary-part digital data word Q₁, and a second complex number, represented as a real-part digital data word I₂ and an imaginary-part digital data word Q₂, comprising:

first and second CORDIC means for rotationally modifying by an angle α

_i , where i is a positive integer, where α

₁ is a selected one of ±

90° and

α

_i, for 2≦

i≦

N and N greater than 2, is tan^-1 (2^-n) with n=i-2, respectively an input real-part digital data word I and an input imaginary-part digital data word Q, responsive in each i-th one of N time intervals to the state of another digital data bit, to respectively obtain an output digital data word Q'"'"' and an output digital data word I'"'"';

the first CORDIC means receiving respective data words I₁ and Q₁ as respective real-part and imaginary-part data words and providing at least one output data word I₀ and a signal which changes sign state when the effective output angle is substantially zero;

the second CORDIC means receiving respective data words I₂ and Q₂ as respective real-part and imaginary-part data words and providing respective real-part and imaginary-part output data words I" and Q";

means for providing in each i-th time interval said another digital data bit with a data state selected to cause both of said CORDIC means to rotationally modify the output digital data words therein until the sign-stage signal changes sign; and

output means receiving the respective output I" and Q" digital data words for respectively providing an imaginary-part I'"'"' of the output digital data and a real-part Q'"'"' of the output digital data word.

17. The apparatus of claim 16, wherein each of the CORDIC means is a recursive CORDIC rotator.

18. The apparatus of claim 17, wherein the output means further comprises:

means receiving the first CORDIC means output data word I₀ ; and

means for scalar multiplying each respective one of the real-part output I" data word and the imaginary-part output Q" digital data word by the I₀ data word to obtain the respective real-part I'"'"' and imaginary-part Q'"'"' digital data words.

19. Apparatus for providing output digital data which is the product of a first complex number, represented as a real-part digital data word I₁ and an imaginary-part digital data word Q₁, and a second complex number, represented as a real-part digital data word I₂ and an imaginary-part digital data word Q₂, comprising:

first and second CORDIC means for rotationally modifying by an angle α

_i, where i is a positive integer, where α

₁ is a selected one of ±

90° and

α

_i, for 2≦

i≦

N and N greater than 2, is tan^-1 (2^-n) with n=i-2, respectively an input real-part digital data word I and an input imaginary-part digital data word Q, with the sign of each angle responsive to the logic state of an associated sign bit;

the sign bit for each angle of the first means being the data bit then present at one of the pair of data inputs for a computing stage for that angle, to respectively obtain an output digital data word Q'"'"' and an output digital data word I'"'"';

a plurality N of means for inverting the logic state of an input bit, each i-th inverting means receiving the sign bit from the stage for the first means for the associated i-th angle and providing another sign bit to the like-numbered i-th stage of the second means;

the second means receiving the respective data words I₂ and Q₂ as respective real-part and imaginary-part data words and providing at least one output word which is the magnitude |A₂ | of the second complex number; and

output means receiving the respective output I'"'"' and Q'"'"' digital data words for respectively providing an imaginary-part Q" of the output digital data and a real-part I" of the output digital data word.

20. The apparatus of claim 19, wherein the output means further comprises:

means receiving the second CORDIC means output data word |A₂ |; and

means for scalar multiplying each respective one of the real-part output I" digital data word and the imaginary-part output Q" digital data word by the |A₂ | data word to obtain the respective real-part I'"'"' and imaginary-part Q'"'"' digital data words.