Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
2000-08-22
2001-11-13
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C341S115000, C341S120000
Reexamination Certificate
active
06317071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to analog-to-digital converters and, more particularly, to an analog-to-digital converter system which combines a plurality of digital sample values to produce a digital output value.
2. Description of Related Art
Many physical devices generate output signals which are analog or continuously varying. Today, signal processing is often accomplished using digital methods. In many applications it is required to convert an analog signal into a digital form suitable for processing by a digital system. Many types of converters exist which act as interfaces between analog devices and digital systems. These converters are used in a variety of applications, including testing, measurement, process control, and communications. In converting analog signals to digital form, the analog signal is typically sampled and quantized. In a typical wireless communications system, a radio frequency (RF) signal comprised of information signals(s) modulated onto RF carrier(s) is received by an antenna. For example, for cellular communications in the United States, information signals are carried over frequency channels within 824-849 MHz and 869-894 MHz. In a Personal Communications System (PCS), information signals are carried over frequency channels on one or more PCS bands 1850 MHz-1910 MHz and 1930-1990 MHz. After some filtering and frequency down-conversion to an intermediate frequency (IF), the analog signals are provided to a low noise amplifier (LNA). The LNA amplifies the analog signals and provides the analog signals to an A/D converter for analog to digital conversion. The A/D converter provides the digital values to a bus which provides the digitized signals to the digital radio circuitry, for example digital downconverters connected to associated digital signal processors.
Today, a fast A/D converter can run at speeds of up to 1 Gigasamples per second (GSps). At the faster speeds, the signal to noise ratio (SNR) of the digital signal from the A/D converter can degrade when the A/D converter clock has imperfections, such as clock jitter. In any event, digital downconverters can only handle maximum data speeds at its input of up to 70 Megasamples per second (MSps). Frequency conversion stages can be used to frequency convert the analog signals to lower IF frequencies, but these add noise and cost. Furthermore, the data rate at the input to the digital downconverters can be reduced by discarding a subset of the digital sample values. However, such schemes fail to take advantage of the higher sampling speed of the A/D converter and introduce noise to the digital signal.
Accordingly, a need exists for analog to digital conversion at higher speeds where effects, such as clock jitter, are reduced and the higher speed sampling of the A/D converter can be taken advantage of in the lower speed digital signal processing circuitry, such as the digital downconverters.
SUMMARY OF THE INVENTION
The present invention is an analog-to-digital (A/D) converter system which converts an analog input signal into a digital output value by combining a plurality of digital sample values. For example, an A/D converter converts an RF analog signal into digital sample values. The A/D system comprises averaging circuitry which takes the average of N digital sample values from the A/D converter. The average is produced as the digital output value for digital processing circuitry. The signal to noise ratio (SNR) of the A/D system is thereby increased because in the averaging process noise components tend to cancel due to their random nature. The increase in the SNR provided by averaging the digital sample values enables the use of higher sampling rates because the processing gain achieved by averaging the digital signal samples counters the degradation caused by clock jitter. As such, a higher speed A/D converter can be used to directly convert an RF analog signal, thereby reducing the need for frequency conversion stages. In certain embodiments, the data rate or speed is reduced to produce digital output values at a data rate compatible with the digital processing circuitry.
REFERENCES:
patent: 4903023 (1990-02-01), Evans et al.
patent: 5563596 (1996-10-01), Snyder et al.
patent: 5610943 (1997-03-01), Kakuishi et al.
patent: 5714956 (1998-02-01), Jahne et al.
patent: 5774470 (1998-06-01), Nishiya et al.
patent: 5825318 (1998-10-01), Patapoutian et al.
Kolsrud Arild
Wu Hui
Alston & Bird LLP
Lucent Technologies - Inc.
Nguyen John B
Young Brian
LandOfFree
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