US5396244A
Expired / Lapsed
US
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Digital-to-analog converter
Assignee: US Philips Corp
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Filing: 1993-11-09
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Granted: 1995-03-07
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Expires: 2013-11-09
Abstract
Abstract A digital-to-analog converter comprises a sigma-delta modulator for generating a 1-bit digital signal (D3) modulated synchronously with a clock signal (NF S ) in response to a digital input signal (D2). This modulator is followed by an asynchronous analog sigma-delta modulator for generating a bivalent asynchronously modulated signal (D4) in response to the synchronously modulated digital signal (D3). The information in the digital signal (D3) from the sigma-delta modulator resides in signal transitions which can appear exclusively at discrete instants defined by the clock signal. The information in the asynchronously modulated signal (D4) from the asynchronous sigma-delta modulator is contained in an analog variation of the duty cycle. This means that the signal transitions of the asynchronously modulated signal (D4) are not tied to a fixed pattern of discrete instants but that all the intervening instants are also available. As a result of the freedom of the positions of the signal transitions, the frequency spectrum of the asynchronously modulated signal (D4) has a substantially smaller width than the frequency spectrum of the synchronously modulated digital signal (D3) from the sigma-delta modulator. This enables an interface to a further signal processing device to be simplified.
Inventors
- 👤 Roza Engel
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 12:23
CPC Classifications
H; H03; H03F; H03F3/00; H03F3/20; H03F3/21; H03F3/217; H03M; H03M3/00; H03M3/30; H03M3/39; H03M3/412; H03F2200/00; H03F2200/331; H03F2200/351; H03M3/50; H03M7/00; H03M7/30; H03M7/3002; H03M7/3004; H03M7/3015; H03M7/302; H03M7/3024; H03M7/3028
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
91 words
A digital-to-analog converter comprising: a sigma-delta modulator for generating a 1-bit digital signal (D3) modulated synchronously with a clock signal (NF S ) in response to a digital input signal (D2), output means for supplying an output signal in response to the synchronously modulated digital signal (D3), and wherein the digital-to-analog converter further comprises an asynchronous sigma-delta modulator for generating a bivalent asynchronously modulated signal (D4) in response to the synchronously modulated digital signal (D3) from the sigma-delta modulator and for supplying the asynchronously modulated signal (D4) to the output means.
Claim 2
Dependent Claim
91 words
A digital-to-analog converter comprising: a sigma-delta modulator for generating a 1-bit digital signal (D3) modulated synchronously with a clock signal (NF S ) in response to a digital input signal (D2), output means for supplying an output signal in response to the synchronously modulated digital signal (D3), and wherein the digital-to-analog converter further comprises an asynchronous sigma-delta modulator for generating a bivalent asynchronously modulated signal (D4) in response to the synchronously modulated digital signal (D3) from the sigma-delta modulator and for supplying the asynchronously modulated signal (D4) to the output means.
Claim 3
Dependent Claim
112 words
A digital-to-analog converter comprising: a sigma-delta modulator having input means for receiving a digital input signal and operative to generate at its output a 1-bit digital signal modulated synchronously with a clock signal in response to said digital input signal, an asynchronous sigma-delta modulator having input means coupled to the output of said sigma-delta modulator to receive said 1-bit synchronously modulated digital signal and being operative in response to the 1-bit synchronously modulated digital signal to generate a bivalent asynchronously modulated signal at its output, an analog output filter means, and an interface circuit coupled between the output of the asynchronous sigma-delta modulator and an input of the analog output filter means.
Claim 4
Dependent Claim
112 words
A digital-to-analog converter comprising: a sigma-delta modulator having input means for receiving a digital input signal and operative to generate at its output a 1-bit digital signal modulated synchronously with a clock signal in response to said digital input signal, an asynchronous sigma-delta modulator having input means coupled to the output of said sigma-delta modulator to receive said 1-bit synchronously modulated digital signal and being operative in response to the 1-bit synchronously modulated digital signal to generate a bivalent asynchronously modulated signal at its output, an analog output filter means, and an interface circuit coupled between the output of the asynchronous sigma-delta modulator and an input of the analog output filter means.
Claim 5
Dependent Claim
83 words
The digital-to-analog converter as claimed in claim 2 further comprising: an input terminal for an M-bit digital signal (D1) having a clock frequency F s , and an upsampling filter coupled between said input terminal and said input means of the sigma-delta modulator and having a sampling input for a clock frequency signal NF s whereby the upsampling filter produces at its output an M-bit digital signal (D2) having a clock frequency NF s , where N is a number greater than 1.
Claim 6
Dependent Claim
26 words
The digital-to-analog converter as claimed in claim 2, wherein said interface circuit comprises an inverter and said analog output filter means comprises a low pass filter.
Claim 7
Dependent Claim
36 words
The digital-to-analog converter as claimed in claim 2 wherein said asynchronous sigma-delta modulator converts an input digital signal (D3) having a wide frequency spectrum into an output digital signal (D4) having a much narrower frequency spectrum.
Claim 8
Dependent Claim
46 words
The digital-to-analog converter as claimed in claim 5 wherein the asynchronous sigma-delta modulator output digital signal (D4) does not include any frequencies above 40 MHz when the input digital signal (D3) comprises a clock frequency of 200 MHz modulated with a sine wave of 1 MHz.
Claim 9
Dependent Claim
135 words
The digital-to-analog converter as claimed in claim 2 wherein: the sigma-delta modulator comprises a cascade connection of a digital differential circuit coupled to the input means of the sigma-delta modulator, a digital low pass filter, and a digital quantizer having an output coupled to the output of the sigma-delta modulator, and a feedback circuit coupled between the output of the digital quantizer and an input of the digital differential circuit, and the asynchronous sigma-delta modulator comprises a cascade connection of an analog differential circuit coupled to the input means of the asynchronous sigma-delta modulator, an analog low pass filter, and an analog comparator having an output coupled to the output of the asynchronous sigma-delta modulator, and a feedback circuit coupled between the output of the analog comparator and an input of the analog differential circuit.
Claim 10
Dependent Claim
28 words
The digital-to-analog converter as claimed in claim 2 wherein the sigma-delta modulator comprises a first integrated circuit and the analog output filter means comprises a second integrated circuit.
Claim 11
Dependent Claim
30 words
The digital-to-analog converter as claimed in claim 2 further comprising a notch filter coupled between the output of the sigma-delta modulator and the input means of the asynchronous sigma-delta modulator.
Claim 12
Dependent Claim
129 words
In a digital video system, a digital-to-analog converter comprising: a sigma-delta modulator having input means for receiving a video frequency digital input signal and operative to generate at its output a 1-bit digital signal modulated synchronously with a clock signal at a frequency that is N times the video frequency in response to said digital input signal, an asychronous sigma-delta modulator having input means coupled to the output of said sigma-delta modulator to receive said 1-bit synchronously modulated digital signal and being operative in response to the 1-bit synchronously modulated digital signal to generate a bivalent asynchronously modulated signal at its output, an analog output filter means, and an interface circuit coupled between the output of the asychronous sigma-delta modulator and an input of the analog output filter means.
Claim 13
Dependent Claim
129 words
In a digital video system, a digital-to-analog converter comprising: a sigma-delta modulator having input means for receiving a video frequency digital input signal and operative to generate at its output a 1-bit digital signal modulated synchronously with a clock signal at a frequency that is N times the video frequency in response to said digital input signal, an asychronous sigma-delta modulator having input means coupled to the output of said sigma-delta modulator to receive said 1-bit synchronously modulated digital signal and being operative in response to the 1-bit synchronously modulated digital signal to generate a bivalent asynchronously modulated signal at its output, an analog output filter means, and an interface circuit coupled between the output of the asychronous sigma-delta modulator and an input of the analog output filter means.
References Cited (Backward Citations)
US5245345A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1998-03-06 | 1998-09-05 | 1999-03-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-03-06 | 2002-09-05 | 2003-03-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-03-06 | 2006-09-05 | 2007-03-07 | $7700.00 | Window Closed / Lapsed |