US4078250A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Log-antilog conversion for a digital radar system
Assignee: Raytheon Co
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Filing: 1976-06-04
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Granted: 1978-03-07
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Expires: 1996-06-04
Abstract
Abstract Linear domain numbers are converted into standard characteristic-mantissa format by left shifting the leading zeros out of the mantissa portion and into the characteristic portion. The resulting normalized mantissa M is separated into a MSB portion m and a LSB portion n: where M= m + n, and m >> n to accomodate the approximate relationship Log (M) ≃ log term + correction term ≃ Log (m) + 2n/2m' + n where m' = the MSB portion of m. Look up tables are provided for supplying the two terms for each mantissa received. The digital radar landmass systems then performs computations using the approximate logs. The answers are returned to the linear domain by an antilog circuit.
Inventors
- 👤 David F. Windsor
- 👤 Kanwalnain S. Rekhi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 23:53
CPC Classifications
G; G06; G06F; G06F1/00; G06F1/02; G06F1/03; G06F1/035; G06F1/0356; G06F2101/00; G06F2101/10
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
217 words
A log-antilog conversion circuit adapted for use in a digital radar landmass system to expediate computations by converting linear domain numbers from the digital radar landmass system into log domain numbers prior to computation by the digital radar landmass system and then converting the log domain numbers into linear domain numbers subsequent to computation, comprising: normalizer means adapted to respond to the linear domain numbers prior to computation to eliminate leading zeros in the linear domain numbers for putting the linear domain numbers into uniform mantissa form; characteristic means adapted to respond to the linear domain numbers prior to computation for calculating the log domain characteristic of the linear domain numbers; log means responsive to the linear domain mantissa for determining the approximate log thereof by providing Log(M) ≅ Log(m) + 2n/2m' + n where M = the mantissa = m + n m >> n m = the MSB portion of M, n = the LSB portion of M, and m' = the MSB portion of m; antilog means responsive to the log domain numbers subsequent to computation for determining the antilog of the log domain mantissa of the log domain number; and binary point means responsive to the log domain numbers subsequent to computation for determining the linear domain binary point of the received logs.
Claim 2
Dependent Claim
217 words
A log-antilog conversion circuit adapted for use in a digital radar landmass system to expediate computations by converting linear domain numbers from the digital radar landmass system into log domain numbers prior to computation by the digital radar landmass system and then converting the log domain numbers into linear domain numbers subsequent to computation, comprising: normalizer means adapted to respond to the linear domain numbers prior to computation to eliminate leading zeros in the linear domain numbers for putting the linear domain numbers into uniform mantissa form; characteristic means adapted to respond to the linear domain numbers prior to computation for calculating the log domain characteristic of the linear domain numbers; log means responsive to the linear domain mantissa for determining the approximate log thereof by providing Log(M) ≅ Log(m) + 2n/2m' + n where M = the mantissa = m + n m >> n m = the MSB portion of M, n = the LSB portion of M, and m' = the MSB portion of m; antilog means responsive to the log domain numbers subsequent to computation for determining the antilog of the log domain mantissa of the log domain number; and binary point means responsive to the log domain numbers subsequent to computation for determining the linear domain binary point of the received logs.
Claim 3
Dependent Claim
37 words
The system of claim 1, wherein the normalizer has a left shifter for eliminating the leading zeros and an encoder in communication with the characteristic means for appropriately compensating the linear domain characteristic of the input number.
Claim 4
Dependent Claim
27 words
The circuit of claim 2, wherein the antilog means further comprises a denormalizer for placing leading zeros in the antilog to establish the desired linear domain characteristics.
Claim 5
Dependent Claim
41 words
The system of claim 3, wherein the denormalizer has a control responsive to the binary point means for establishing the desired linear domain binary point, and a right shifter responsive to the control for placing the appropriate number of leading zeros.
Claim 6
Dependent Claim
36 words
The system of claim 4, wherein the log means has a log table and a correction table for interpolating between the entries of the log tables, and an adder for combining outputs of the two tables.
Claim 7
Dependent Claim
37 words
The system of claim 5, wherein the antilog means has an antilog table and a correction table for interpolating between the entries of the log table, and an adder for combining the outputs of the two tables.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1981-03-06 | 1981-09-05 | 1982-03-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-03-06 | 1985-09-05 | 1986-03-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-03-06 | 1989-09-05 | 1990-03-07 | $7700.00 | Window Closed / Lapsed |