Polyphase filter with stack shift capability
AssigneeNorthrop Grumman Corporation
InventorsHanna S-H. Hsu, Maneesh Goyal, Jeffrey B. Warner, Ronald P. Smith
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Abstract
A discrete Fourier transform (DFT) filter bank with stack shift capability, configured, for example, as an analyzer, but equally applicable to a synthesizer, and implemented as a polyphase filter. The DFT filter bank includes a complex modulator for multiplying the input signals x0(m), x1(m) . . . xM−1(m) by a complex modulator e−2πko(m). In order to keep the coefficients for the polyphase filter real, the coefficients are modulated by a DFT twiddle factor e−2πkoρ/M. The use of the DFT twiddle factor enables the hardware to be reduced significantly. For example, for an 8 phase 203 tap filter, only 8 selectable negators are required as opposed to 211 for known DFT filter banks.
Claims7
A frequency analyzer for analyzing a plurality of input signals x0(m) . . . x1(m) . . . xM−1(m), the frequency analyzer comprising:
- a plurality of input modulators for modulating and shifting said input signals xo(m) . . . x1(m) . . . xM−1(m), defining shifted output signals, wherein said plurality of input modulators include a multiplier for multiplying each of said input signals xo(m) . . . x1(m) . . . xM−1(m) by a factor e−jωn, where n is a time index;
- a polyphase filter network which includes a plurality of polyphase filters po(m) . . . pρ(m) . . . pM−1(m), each having a coefficient for receiving said shifted output signals and defining polyphase filter output signals;
- and
- a plurality of output modulators for modulating the output of said polyphase filters, said frequency analyzer configured to process said plurality of input signals xo(m) . . . x1(m) . . . xM−1(m), wherein each of said plurality of polyphase filters includes a network coefficient and said output modulators include a multiplier for multiplying the output of each of said polyphase filters by a predetermined factor selected so that said coefficients are real.
A polyphase filter comprising:
- a plurality of filter channels,
- {overscore (p)}0(m) . . . {overscore (p)}p(m) . . . {overscore (p)}M−1(m)
- for filtering a plurality of input signals x0(m) . . . xp(m) . . . xM−1(m), and
- a plurality of output modulators for modulating each of the outputs of said plurality filter channels by a modulation factor, wherein each of said input signals are modulated by a complex modulator which modulates each input signal x0(m) . . . xp(m) . . . xM−1(m) by a factor (−1)m, where m is the time index and wherein each of said plurality of filter channels includes a coefficient and said output modulators include a multiplier for multiplying the output of each of said filter channels by a factor selected so that said coefficients are real.
A frequency synthesizer for analyzing a plurality of input signals xo(m) . . . x1(m) . . . xM−1(m), the frequency analyzer comprising:
- a plurality of input modulators for modulating and shifting said input signals xo(m) . . . x1(m) . . . xM−1(m), defining shifted output signals;
- a polyphase filter network which includes a plurality of polyphase filters po(m) . . . pρ(m) . . . pM−1(m), each having a coefficient for receiving said shifted output signals and defining polyphase filter output signals;
- and
- a plurality of output modulators for modulating the output of said polyphase filters, said frequency synthesizer configured to combine said polyphase filter output signals and provide a single output signal, said output modulators include a multiplier for multiplying the output of each of said plurality of polyphase filters po(m) . . . pρ(m) . . . pM−1(m) by a predetermined factor selected so that said coefficients are real.
Dependencies are inferred from the claim text.