Digital to analog resolver converter
AssigneeThe Singer Company
InventorsDavid J. Simon, Edward C. Costello
Life of this patent
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Abstract
A digital to analog resolver converter uses a digital to analog converter to convert a part of the digital input to a corresponding analog angle value. This analog angle value is applied to sine and cosine function generators which use the equations of chords to approximate the value of the sine and cosine functions in one octant. Bits of the digital input are used to select slope values from the chord equations for approximating the sine and cosine of the analog angle value. The digital to analog resolver converter uses the minimum number of precision resistors to generate the sine and cosine slope and intercept values for the equations of a given number of approximating chords.
Claims10
In a method utilizing electronic circuitry for converting an m bit digital voltage signal representing an angle over an octant which is a portion of an n bit digital voltage signal representing an angle from 0.degree. to 360.degree. into an analog voltage signal representing a continuous periodic function of the angle to be used as an output of a digital to analog resolver converter comprising:
- a. dividing the continuous periodic function of the angle into an even number p of equal angular segment each segment having a slope with the same sign over the full segment where log.sub.2 p is a non-negative integer;
- b. determining and storing average slope and intercept information of each slope segment in electronic circuitry;
- c. converting the r least significant bits of the digital signal into an analog value in a digital to analog converter where r = m -log.sub.2 p;
- d. selecting in said electronic circuitry slope and intercept values in accordance with the remaining log.sub.2 p bits of the m bit digital voltage signal and the (m-1) th bit;
- and
- e. carrying out multiplication of the converted analog value by a selected slope and addition of selected intercept values in electronic circuitry, the improvement comprising;
- f. determining and storing in said electronic circuitry, as a first intercept, the intercept of a line segment subtending one of said angular segments;
- g. determining and storing the slopes of line segments subtending each of said angular segments in said electronic circuitry;
- h. selecting one of the slopes as the slope multiplier in accordance with the remaining log.sub.2 p bits in said electronic circuitry;
- i. determining a partial intercept value in said electronic circuitry;
- and
- j. multiplying the analog value by the selected slope multiplier and adding to the results the partial intercept value and the first intercept in said electronic circuitry.
In a device for converting an m bit digital signal representing an angle between first and second limits into an analog signal representing a continuous periodic function of the angle comprising:
- a. means for storing the slopes of line segments subtendng a number p, where log.sub.2 p is non-negative integer, an equal angular segments which divide the continuous periodic function between the first and second limits;
- b. means for storing intercept information;
- c. means for converting the least significant r bits of the digital signal into an anlog signal where r = m - log.sub.2 p;
- d. means for selecting slope and intercept information in accordance with the remaining log.sub.2 p bits and
- e. means for multiplying the analog signal by the slope multiplier and adding intercept values thereto, the improvement comprising:
- f. the means for storing intercept information storing the intercept of one of said line segments as a first intercept;
- and
- g. the means for selecting being means to select one slope as a slope multiplier and the value 0 or the sum of the other slopes as a partial intercept in accordance with the remaining log.sub.2 p bits;
- and
- h. the means for multiplying and adding being means to multplying the analog signal by the slope multiplier and add to the signal the sum of the first intercept and partial intercept.
In a digital to analog resolver converter for generating a sine and cosine signal for all angles between 0.degree. and 360.degree., where n bits of a digital input signal represent an angle between 0.degree. and 360.degree., comprising:
- a. a digital to analog converter for converting the sixth to nth bits of the digital input signal into an equivalent analog output signal and multiplying the equivalent analog output signal by a reference voltage to produce an analog output signal;
- b. complement command means for complementing the analog output signal if the third bit is present indicating that the angle is in an even numbered octant;
- c. sine storage means for storing sine slope and intercept values;
- d. cosine storage means for storing cosine slope and intercept values;
- e. segment computation means for determining the angular segment Z in which the angle represented by the analog output signal lies;
- f. slope and intercept selection means;
- g. cosine computation means;
- h. sine computation means;
- i. octant and sign select means for
- i. coupling the cosine function output to the cosine output and sine function output to the sine output if the second and third bits of the digital input signal have identical values, otherwise coupling the sine function output to the cosine output and the cosine function output to the sine output;
- ii. inverting said sine output voltage if the first bit is present indicating the magnitude of the angle is greater than 180.degree.;
- and
- iii. inverting said cosine output voltage if the first and second bits are identical, the improvement comprising:
- j. said sine storage means comprising:
- i. a plurality of sine slope storage means each with an input and output for storing as first through fourth sine slope values the slope of line segments subtending four equal angular segments of the first octant of the sine function;
- k. said cosine storage means comprising:
- i. a plurality of cosine slope storage means each with an input and output for storing as first through fourth cosine slope values the slopes of the line segments subtending four equal angular segments of the first octant of the cosine function;
- and
- ii. cosine intercept storage means with an input connected to the negative of the reference voltage and an output for storing as the first cosine intercept value the intercept of the line segment subtending the first angular segment of the first octant of the cosine function;
- l. said slope and intercept selection means comprising means for:
- i. connecting the input of one cosine slope storage means to the analog output signal to establish a cosine slope voltage;
- ii. connecting the input of one sine slope storage means to the analog output signal to establish a sine slope voltage;
- iii. connecting the inputs of the remaining cosine slope storage means to one of ground and the reference voltage to establish a partial cosine intercept voltage;
- and
- iv. connecting the inputs of the remaining sine slope storage means to one of ground and the reference voltage to establish a sine intercept voltage;
- m. said cosine computation means comprising means with inputs connected to the output of the cosine slope storage means and the output of the cosine intercept storage means for generating a cosine function output voltage equal to the sum of the cosine slope voltage, partial cosine intercept voltage and the voltage on the output of the cosine intercept storage means;
- and
- n. said sine computation means comprising means connected to the outputs of the sine slopes storage means for generating a sine function output equal to the sum of the sine slope voltage and the sine intercept voltage.
Dependencies are inferred from the claim text.