Direct downconverter circuit for demodulator in digital data transmission system
First Claim
1. A digital downconverter circuit for a digital data transmission system, comprising:
- an input for receiving an analog intermediate frequency (IF) carrier signal onto which baseband information has been modulated;
a bandpass filter circuit for filtering said received analog IF carrier signal and outputting a bandpass analog IF signal;
an analog-to-digital converter for converting said bandpass analog IF signal into a bandpass digital IF signal;
a phase shifter device for outputting a complex pair of phase shifted baseband signals operating at a local baseband frequency;
a digital mixer device for mixing said bandpass digital IF signal separately with each of said complex pair of phase shifted baseband signals and outputting a complex combined baseband/bandpass signal comprising in-phase and quadrature components;
filtering circuitry for recovering baseband information from said in-phase and quadrature components of said complex combined baseband/bandpass signal and outputting information-bearing in-phase and quadrature baseband signals, said filtering circuitry including a half-band pre-filter and a low pass filter; and
sampling circuitry operating at a predetermined sampling frequency for sampling said information-bearing recovered baseband signals and outputting a sampled complex baseband output signal.
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Accused Products
Abstract
A digital downconverter circuit for a digital data transmission system is provided, comprising (i) a bandpass filter circuit for filtering a received analog intermediate frequency (IF) carrier signal onto which baseband information has been modulated, and outputting a bandpass analog IF signal; (ii) an analog-to-digital converter for converting the bandpass analog IF signal into a bandpass digital IF signal; (iii) a phase shifter device for outputting a complex pair of phase shifted baseband signals operating at a local baseband frequency; (iv) a mixer device for mixing the bandpass digital IF signal separately with each of the complex pair of phase shifted baseband signals and outputting a complex combined baseband/bandpass signal comprising inphase and quadrature components; (v) filtering circuitry for recovering the baseband information onto the phase shifted baseband signals; and (vi) sampling circuitry for sampling the information-bearing recovered baseband signals and outputting a sampled complex baseband output signal. The phase shifter device, the mixer device, the filtering circuitry, and the sampling circuitry are all implemented on a gallium arsenide (GaAs) application specific integrated circuit (ASIC). The filtering circuitry includes a single half-band pre-filter and a multi-pole low pass filter. The analog-to-digital converter operates at the sampling clock frequency, which is about 512 megahertz (MHz), and the IF carrier signal operates at about 52-176 MHz. An automatic gain control circuit controls the amplitude of the bandpass analog IF signal prior to its being converted into the bandpass digital IF signal.
161 Citations
27 Claims
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1. A digital downconverter circuit for a digital data transmission system, comprising:
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an input for receiving an analog intermediate frequency (IF) carrier signal onto which baseband information has been modulated; a bandpass filter circuit for filtering said received analog IF carrier signal and outputting a bandpass analog IF signal; an analog-to-digital converter for converting said bandpass analog IF signal into a bandpass digital IF signal; a phase shifter device for outputting a complex pair of phase shifted baseband signals operating at a local baseband frequency; a digital mixer device for mixing said bandpass digital IF signal separately with each of said complex pair of phase shifted baseband signals and outputting a complex combined baseband/bandpass signal comprising in-phase and quadrature components; filtering circuitry for recovering baseband information from said in-phase and quadrature components of said complex combined baseband/bandpass signal and outputting information-bearing in-phase and quadrature baseband signals, said filtering circuitry including a half-band pre-filter and a low pass filter; and sampling circuitry operating at a predetermined sampling frequency for sampling said information-bearing recovered baseband signals and outputting a sampled complex baseband output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for recovering baseband information from a carrier signal which has been modulated onto an intermediate frequency (IF) carrier signal, the method comprising the steps of:
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receiving an analog intermediate frequency (IF) carrier signal onto which baseband information has been modulated; filtering said received analog IF carrier signal using a bandpass filter circuit and outputting a bandpass analog IF signal; converting said bandpass analog IF signal into a bandpass digital IF signal using an analog-to-digital converter; outputting a complex pair of phase shifted baseband signals operating at a local baseband frequency using a phase shifter device; mixing said bandpass digital IF signal, using a digital mixer device, separately with each of said complex pair of phase shifted baseband signals and outputting a complex combined baseband/bandpass signal comprising in-phase and quadrature components; recovering, using filtering circuitry including a half-band pre-filter and a low pass filter, said baseband information from said in-phase and quadrature components of said complex combined baseband/bandpass signal, and outputting information-bearing in-phase and quadrature baseband signals; and sampling said information-bearing recovered baseband signals using sampling circuitry operating at a sampling frequency and outputting a sampled complex baseband output signal. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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Specification