US5450083A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Two-stage decimation filter
Assignee: Analog Devices Inc
•
Filing: 1994-03-09
•
Granted: 1995-09-12
•
Expires: 2014-03-09
Abstract
Abstract A digital filter includes a pre-filter cascaded to a low pass filter. The pre-filter has a transfer function providing generally increasing attenuation with increasing frequency above a cutoff frequency. The low pass filter has a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency. The low pass filter is an FIR filter including coefficients restricted to the set {+1, 0 and -1}. The filters are preferably implemented using simple hardware such as addressable read/write RAM, digital adder/subtracters, and registers. Alternatively, the addressable RAM can be replaced with shift registers. Such a filter is easily and economically implemented and has a favorable overall frequency response characteristic. The filter is, therefore, well suited for use in many digital applications and, in particular, for use as a decimation filter in an oversampled, multi-bit, high order analog-to-digital converter system.
Inventors
- 👤 Robert J. Brewer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 23:34
CPC Classifications
H; H03; H03H; H03H17/00; H03H17/02; H03H17/06; H03H17/0621; H03H17/0635; H03H17/065; H03H17/0664
Claims Analysis
Total Claims: 27
Claim 1
Independent Claim
104 words
A digital decimation filter for use in an oversampled analog-to-digital converter system comprising: a pre-filter receiving an input digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, wherein the low pass filter is an FIR filter including filter coefficients restricted to the set {+1, 0 and -1}.
Claim 2
Dependent Claim
104 words
A digital decimation filter for use in an oversampled analog-to-digital converter system comprising: a pre-filter receiving an input digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, wherein the low pass filter is an FIR filter including filter coefficients restricted to the set {+1, 0 and -1}.
Claim 3
Dependent Claim
30 words
A digital decimation filter as claimed in claim 1 wherein the pre-filter includes means for producing a running sum of a finite number of samples of the input digital signal.
Claim 4
Dependent Claim
70 words
A digital decimation filter as claimed in claim 2 wherein the means for producing comprises: a first memory element storing the finite number of samples of the input digital signal; and a digital adder/subtracter, coupled to the first memory element, for selectively adding to the running sum a new sample in the first memory element and selectively subtracting from the running sum a last sample in the first memory element.
Claim 5
Dependent Claim
32 words
A digital decimation filter as claimed in claim 3 wherein the means for producing further includes a second memory element, coupled to the digital adder/subtracter, and operative to store the running sum.
Claim 6
Dependent Claim
18 words
A digital decimation filter as claimed in claim 4 wherein the first memory element includes a shift register.
Claim 7
Dependent Claim
22 words
A digital decimation filter as claimed in claim 4 wherein the first memory element includes an addressable read/write random access memory element.
Claim 8
Dependent Claim
19 words
A digital decimation filter as claimed in claim 1 wherein the input digital signal is a 1-bit digital stream.
Claim 9
Dependent Claim
18 words
A digital filter as claimed in claim 1 wherein the input digital signal is an n-bit digital stream.
Claim 10
Dependent Claim
131 words
An analog-to-digital converter system comprising: an oversampled analog-to-digital converter, receiving as an input, an analog signal and providing, as an output, a digital signal; and a digital decimation filter, coupled to the analog-to-digital converter, the digital decimation filter comprising: a pre-filter coupled to receive the digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, wherein the low pass filter is an FIR filter including filter coefficients restricted to the set {+1, 0 and -1}.
Claim 11
Dependent Claim
131 words
An analog-to-digital converter system comprising: an oversampled analog-to-digital converter, receiving as an input, an analog signal and providing, as an output, a digital signal; and a digital decimation filter, coupled to the analog-to-digital converter, the digital decimation filter comprising: a pre-filter coupled to receive the digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, wherein the low pass filter is an FIR filter including filter coefficients restricted to the set {+1, 0 and -1}.
Claim 12
Dependent Claim
18 words
An analog-to-digital converter system as claimed in claim 9 wherein the analog-to-digital converter is a sigma-delta analog-to-digital converter.
Claim 13
Dependent Claim
29 words
An analog-to-digital converter system as claimed in claim 10 wherein the pre-filter includes means for producing a running sum of a finite number of samples of the digital signal.
Claim 14
Dependent Claim
67 words
An analog-to-digital converter system as claimed in claim 13 wherein the means for producing comprises: a first memory element storing the finite number of samples of the digital signal; and a digital adder/subtracter, coupled to the first memory element, for adding to the running sum a new sample in the first memory element and subtracting from the running sum a last sample in the first memory element.
Claim 15
Dependent Claim
32 words
An analog-to-digital converter system as claimed in claim 12 wherein the means for producing further includes a second memory element, coupled to the digital adder/subtracter, and operative to store the running sum.
Claim 16
Dependent Claim
18 words
An analog-to-digital converter system as claimed in claim 13 wherein the first memory element includes a shift register.
Claim 17
Dependent Claim
22 words
An analog-to-digital converter system as claimed in claim 13 wherein the first memory element includes an addressable read/write random access memory element.
Claim 18
Dependent Claim
53 words
An analog-to-digital converter system as claimed in claim 13 wherein the second memory element is initialized by setting the value of the second memory element to zero while the input to the analog-to-digital converter is connected to an analog potential for which the output of the analog-to-digital converter is desired to be zero.
Claim 19
Dependent Claim
24 words
An analog-to-digital converter system as claimed in claim 9 wherein the digital signal is an n-bit digital stream where n is a positive integer.
Claim 20
Independent Claim
103 words
A method for decimating a digital input signal comprising the steps of: receiving the digital input signal from an oversampled analog-to-digital converter; pre-filtering the digital input signal with a pre-filter having a transfer function providing generally increasing attenuation with increasing frequency above a cutoff frequency, to produce an intermediate output signal; and using an FIR filter including filter coefficients restricted to the set {+1, 0 and -1}, low pass filtering the intermediate output signal with a low pass filter, coupled to the pre-filter, having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, to produce an output signal.
Claim 21
Independent Claim
103 words
A method for decimating a digital input signal comprising the steps of: receiving the digital input signal from an oversampled analog-to-digital converter; pre-filtering the digital input signal with a pre-filter having a transfer function providing generally increasing attenuation with increasing frequency above a cutoff frequency, to produce an intermediate output signal; and using an FIR filter including filter coefficients restricted to the set {+1, 0 and -1}, low pass filtering the intermediate output signal with a low pass filter, coupled to the pre-filter, having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, to produce an output signal.
Claim 22
Dependent Claim
86 words
A digital decimation filter for use in a multi-bit oversampled analog-to-digital converter system comprising: a pre-filter, receiving a multi-bit input digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency.
Claim 23
Dependent Claim
86 words
A digital decimation filter for use in a multi-bit oversampled analog-to-digital converter system comprising: a pre-filter, receiving a multi-bit input digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency.
Claim 24
Dependent Claim
115 words
A multi-bit analog-to-digital converter system comprising: a multi-bit oversampled analog-to-digital converter, receiving as an input, an analog signal and providing, as an output, a multi-bit digital signal; and a digital decimation filter, coupled to the analog-to-digital converter, the digital decimation filter comprising: a pre-filter coupled to receive the multi-bit digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency.
Claim 25
Dependent Claim
115 words
A multi-bit analog-to-digital converter system comprising: a multi-bit oversampled analog-to-digital converter, receiving as an input, an analog signal and providing, as an output, a multi-bit digital signal; and a digital decimation filter, coupled to the analog-to-digital converter, the digital decimation filter comprising: a pre-filter coupled to receive the multi-bit digital signal and providing an intermediate output signal, the transfer function of the pre-filter providing generally increasing attenuation with increasing frequency above a predetermined cutoff frequency; and a low pass filter, coupled to receive the intermediate output signal from the pre-filter and providing an output digital signal, the low pass filter having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency.
Claim 26
Independent Claim
92 words
A method for decimating a multi-bit digital input signal comprising the steps of: receiving the multi-bit digital input signal from a multi-bit oversampled analog-to-digital converter; pre-filtering the multi-bit digital input signal with a pre-filter having a transfer function providing generally increasing attenuation with increasing frequency above a cutoff frequency, to produce an intermediate output signal; and low pass filtering the intermediate output signal with a low pass filter, coupled to the pre-filter, having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, to produce an output signal.
Claim 27
Independent Claim
92 words
A method for decimating a multi-bit digital input signal comprising the steps of: receiving the multi-bit digital input signal from a multi-bit oversampled analog-to-digital converter; pre-filtering the multi-bit digital input signal with a pre-filter having a transfer function providing generally increasing attenuation with increasing frequency above a cutoff frequency, to produce an intermediate output signal; and low pass filtering the intermediate output signal with a low pass filter, coupled to the pre-filter, having a transfer function providing substantially decreasing attenuation with increasing frequency above the cutoff frequency, to produce an output signal.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1998-09-11 | 1999-03-13 | 1999-09-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-09-11 | 2003-03-13 | 2003-09-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-09-11 | 2007-03-13 | 2007-09-12 | $7700.00 | Window Closed / Lapsed |