EP0458452A2
Expired / Lapsed
EP
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Quadrature demodulator
Assignee: Nokia Mobile Phones UK Ltd
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Filing: 1991-04-11
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Granted: —
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Expires: 2011-04-11
Abstract
Abstract A quadrature demodulator for deriving an in-phase (I) and quadrature (Q) component from an input RF signal comprises means (24,25) for down-converting the RF signal to an IF signal. The IF signal is sampled (27) and digitised by an ADC (28). A complex digital filter (29) is used as a phase splitter designed to pass the positive IF frequency +f₀ but block the negative IF frequency -f₀. The resultant complex signal is in IQ form. By using four times oversampling at the ADC (28) the digital filter (29) can be split cleanly into two smaller filter sections (30, 31). By using feedforward filters for both these filter sections (30 and 31) a high degree of phase linearity can be achieved with minimal distortion.
Inventors
- 👤 Samuel Ng
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 13:16
CPC Classifications
H; H03; H03D; H03D1/00; H03D1/22; H03D1/2245; H03D1/02; H03D1/06
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
88 words
A demodulating arrangement for deriving an in-phase (I) and quadrature (Q) output signal from an input radio frequency (RF) signal, comprising RF signal input means, means for down-converting said RF signal to an intermediate frequency (IF) signal, means for sampling said IF signal, means for digitising the sampled signal, digital filter means comprising two feedforward filter sections, and means for applying the digitised signal sample selectively to the two sections of said digital filter means whereby I and Q signals are output from the two filter sections respectively.
Claim 2
Dependent Claim
68 words
A demodulating arrangement as claimed in claim 1, wherein the digital filter means is adapted to pass a band of frequencies including the positive value of frequency (+f o ) corresponding to the frequency (f o ) of the IF signal and to attenuate a band of frequencies including the negative value of frequency (-f o ) corresponding to the frequency (f o ) of the IF signal.
Claim 3
Dependent Claim
72 words
A demodulating arrangement as claimed in claim 2, wherein the digital filter means is adapted to pass a band of frequencies substantially centred on the positive value of frequency (+f o ) corresponding to the frequency (f o ) of the IF signal and to attenuate a band of frequencies substantially centred on the negative value of frequency (-f o ) corresponding to the frequency (f o ) of the IF signal.
Claim 4
Dependent Claim
34 words
A demodulating arrangement as claimed in any of the preceding claims, wherein the sampling means is adapted to sample the IF signal at an integral multiple of four times the data symbol transmission rate.
Claim 5
Dependent Claim
39 words
A demodulating arrangement as claimed in any of the preceding claims, including means for sampling the output from the two feedforward filter sections at a rate substantially equal to an integral multiple of the IF frequency (f o ).
Claim 6
Dependent Claim
35 words
A demodulating arrangement as claimed in any of the preceding claims, wherein the two sections of the digital filter means each comprise a tapped delay line, having an unequal number of taps in each section.
Claim 7
Dependent Claim
34 words
A demodulating arrangement as claimed in claim 6, wherein one of the two sections of said digital filter means has one more tap than the other of the two sections of said filter means.
Claim 8
Dependent Claim
41 words
A demodulating arrangement as claimed in any of the preceding claims, wherein the down converting means is adapted to down-convert the RF signal to an intermediate frequency the value of which is an integral multiple of the data symbol transmission rate.
Claim 9
Dependent Claim
35 words
A demodulating arrangement as claimed in claim 8, wherein the down-converting means is adapted to down-convert the RF signal to an intermediate frequency the value of which is equal to the data symbol transmission rate.
Claim 10
Dependent Claim
47 words
A demodulating arrangement as claimed in any of claims 1 to 8, wherein the down-converting means is adapted to down-convert the RF signal to an intermediate frequency the value of which is a factor of (n-¾) times the data symbol transmission rate, where n is an integer.
References Cited (Backward Citations)
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