Sampling system for radio frequency receiver

A radio frequency (rf) receiver comprising:

• an input terminal adapted to receive one or more of a number of different digitally modulated rf input signals, including quadrature amplitude modulated (QAM) and vestigial side band (VSB) rf input signals;
• a converting means having an input and an output, said converting means including a first mixer and a second mixer, each of said mixers having an input and an output, a first local oscillator (LO1) and a second local oscillator (LO2), each local oscillator having an output at which is produced a frequency signal, means coupling an output of LO1 and the rf input signals to the input of the first mixer, means coupling the output of the first mixer to an input of a first bandpass filter (BPF1) having a first center frequency (fc1) and a bandwidth of Bhz to produce at an output of BPF1 a first output signal (fo1) having a first center frequency of fc1 with a bandwidth of Bhz, means coupling the output of BPF1 and an output of LO2 to an input of the second mixer for down converting the rf signal, and, means coupling the output of the second mixer to an input of a second bandpass filter (BPF2), said BPF2 having a second center frequency (fc2) and a bandwidth of Bhz, and BPF2 having an output defining the output of said converting means for producing thereat an intermediate frequency (IF) signal whose center frequency is equal to fc2 and whose bandwidth is equal to Bhz;
• and
• a sampling means having an input coupled to the output of said converting means for digitally sampling the intermediate frequency signal and having an output for producing thereat base band signals in response to the rf input signals, said sampling means including a sample and hold circuit (S/H) having an input, an output and a clocking input, a low pass filter having an input and an output, an analog-to-digital converter (ADC) having an input, an output and a clocking input, means coupling the input of the S/H to the output of the converting means and the output of the S/H to the input of the low pass filter, means coupling the output of the low pass filter to the input of the ADC, and, means for applying a sampling signal having a frequency f3 to the clocking input of the S/H and for applying a sampling signal having a frequency f4 to the clocking input of the ADC, wherein f is a rational multiple of f4, and, wherein said sampling means is capable of producing at its output an in-phase (I) base band signal and a quadrature (Q) base band signal in response to a QAM rf input signal and an in-phase (I) baseband signal in response to a VSB rf input signal.

A radio frequency (RF) receiver adapted to receive digitally modulated signals including quadrature amplitude modulated (QAM) and vestigial side band (VSB) RF signals, comprising:

• an input terminal adapted to receive a digitally modulated RF signal, said input terminal having an output which comprises said RF signal with a frequency band centered at a first center frequency;
• a signal conditioning circuit electrically coupled to said input terminal, said signal conditioning circuit receiving said RF signal and producing a first intermediate frequency (IF) signal centered at a first intermediate center frequency;
• a sample and hold circuit electrically coupled to said signal conditioning circuit, said sampling and hold circuit producing a second IF signal centered at a second intermediate center frequency;
• a filter electrically coupled to said sample and hold circuit, said filter isolating said second IF signal;
• an analog to digital (A/D) converter electrically coupled to said filter, said A/D converter producing a digitized IF signal from said second IF signal;
• and
• a demodulator circuit electrically coupled to said A/D converter, said demodulator circuit adapted to demodulate said digitized IF signal, producing a baseband signal.

A radio frequency (RF) receiver, comprising:

• an input terminal adapted to receive a digitally modulated RF signal, said input terminal having an output which comprises said RF signal with a frequency band centered at an initial center frequency;
• a signal conditioning circuit electrically coupled to said input terminal, said signal conditioning circuit receiving said RF signal and producing a first intermediate frequency (IF) signal centered at a first intermediate center frequency;
• an analog to digital (AID) converter electrically coupled to said signal conditioning circuit, said A/D converter receiving said first IF signal and producing a digitized IF signal centered at a second intermediate center frequency;
• and
• a demodulator circuit electrically coupled to said A/D converter, said demodulator circuit adapted to demodulate said digitized IF signal by converting said digitized IF signal into a baseband signal using a demodulation angle which is a function of e.sup.(-j.omega..sbsp.c.sub.nT.sbsp.s.sub.) where .omega..sub.c =2.pi.f.sub.c, T.sub.s =1/f.sub.s, n is an integer, f.sub.c is said second intermediate center frequency, and f.sub.s is the sampling frequency at which said A/D converter samples said second IF signal, wherein f.sub.s is equal to Kf.sub.c, where K is a rational number, thereby reducing said demodulation angle to ##EQU4##

A down converting circuit for the conversion of an intermediate radio frequency (RF) signal converted from a RF signal input to a second intermediate frequency (IF) signal which is located at a substantially lower center frequency than said intermediate radio frequency, said second intermediate frequency (IF) signal being processed thereafter by a demodulating circuit in a RF receiver, comprising:

• a sample and hold circuit with a signal input, a signal output and a clocking input, wherein said intermediate RF signal input is applied to said signal input;
• an anti-aliasing low pass filter (AALPF) having an input coupled to the output of said sample and hold circuit and having an output;
• an analog to digital (A/D) converter having a signal input coupled to the output of said AALPF, a signal output coupled to said demodulating circuit, and a clocking input;
• and
• a first sampling signal with a frequency f.sub.1 applied to the clocking input of said sample and hold circuit, and, a second sampling signal with a frequency f.sub.2 applied to the clocking input of said A/D converter, where f.sub.1 is a multiple of f.sub.2.