All-digital quadrature modulator
First Claim
1. A digital modulator for generating a quadrature modulated signal, said modulator comprising:
- first means for formatting an input data signal into a digital representation of in-phase (I) and quadrature-phase (Q) data signals, including first memory means for storing data and for providing said digital representation of said in-phase (I) and said quadrature-phase (Q) data signals in response to said input data signal;
means for providing a digital carrier signal representative of an integer multiple of a bit clock signal;
second means for formatting said digital carrier signal into a digital representation of in-phase (I) and quadrature-phase (Q) carrier signals, including second memory means for storing data and for providing said digital representation of said in-phase (I) and said quadrature-phase (Q) carrier signals in response to said digital carrier signal;
means, including said second memory means, for storing a digital representation of a quadrature modulated signal, and for providing said digital representation of said quadrature modulated signal in response to said in-phase (I) and quadrature-phase (Q) data signals and said in-phase (I) and quadrature-phase (Q) carrier signals; and
means for converting said digital representation of said quadrature modulated signal into an analog output signal having a precise modulation index.
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Accused Products
Abstract
A CPFSK quadrature modulator (300) is disclosed utilizing an all-digital implementation. The serial data input signal (20 ) is formatted into parallel overlapping bits using a shift register (202), an up/down counter (206), and an interpolation counter (204) and applied as address lines to in-phase and quadrature-phase memories (208, 210). A multiple of the bit clock is used to address carrier generation ROMs (216, 218). The carrier signal is then modulated by the in-phase and quadrature-phase data signals (212, 214, 222), converted to an analog signal by a D/A converter (250), and low pass filtered (254) to generate the analog output signal (255). A single ROM (440) is utilized to implement all the look-up tables, multipliers, and adder. The all-digital implementation allows for precise control of the modulation index to h═0.5±0.05 percent over time, temperature, power levels, etc.
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Citations
48 Claims
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1. A digital modulator for generating a quadrature modulated signal, said modulator comprising:
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first means for formatting an input data signal into a digital representation of in-phase (I) and quadrature-phase (Q) data signals, including first memory means for storing data and for providing said digital representation of said in-phase (I) and said quadrature-phase (Q) data signals in response to said input data signal; means for providing a digital carrier signal representative of an integer multiple of a bit clock signal; second means for formatting said digital carrier signal into a digital representation of in-phase (I) and quadrature-phase (Q) carrier signals, including second memory means for storing data and for providing said digital representation of said in-phase (I) and said quadrature-phase (Q) carrier signals in response to said digital carrier signal; means, including said second memory means, for storing a digital representation of a quadrature modulated signal, and for providing said digital representation of said quadrature modulated signal in response to said in-phase (I) and quadrature-phase (Q) data signals and said in-phase (I) and quadrature-phase (Q) carrier signals; and means for converting said digital representation of said quadrature modulated signal into an analog output signal having a precise modulation index. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A digital quadrature modulator for generating a continuous-phase frequency-shift keyed (CPFSK) signal, said modulator comprising:
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means for translating serial input data having a predetermined bit rate into parallel input data; means for determining the phase quadrant of said serial input data in response to said bit rate and said parallel input data, thereby providing a phase control signal; means for interpolating between data bits of said serial input data, thereby providing an interpolation signal; and memory means for providing a digital representation of a CPFSK signal in response to said parallel input data, said phase control signal, and said interpolation signal. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
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17. A digital modulator for generating a quadrature modulated signal, said modulator comprising:
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first means for transforming a serial data signal into a parallel data signal including first memory means for storing data and providing a digital representation of in-phase (I) and quadrature-phase (Q) data signals in response to said serial data signal; means for providing a radio frequency (RF) carrier signal representative of an integer multiple of a bit clock signal; second means for transforming said radio frequency (RF) carrier signal into a digital carrier signal including second memory means for storing data and for providing a digital representation of in-phase (I) and quadrature-phase (Q) carrier signals in response to said digital carrier signal; means, including said second memory means, for digitally modulating said digital representation of I and Q carrier signals with said digital representation of I and Q data signals, thereby providing a digital representation of a quadrature modulated signal; and means for converting said digital representation of said quadrature modulated signal into an analog output signal having a precise modulation index, whereby digital-to-analog conversion is performed subsequent to quadrature modulation. - View Dependent Claims (18, 19, 20, 21, 22)
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23. A means for generating an analog continuous-phase frequency-shift keyed (CPFSK) signal s(t) by quadrature modulating a radio frequency (RF) carrier fc with an input signal d(t) utilizing entirely digital circuitry, comprising:
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means for providing a data vector d of length L in response to d(t), wherein d has a bit rate 1/T; means for determining a phase parameter of d(t) in response to d , thereby providing a phase signal θ
(t,d );means for providing an interpolation signal having a clock rate M/T; memory means for providing a digital output signal s(t,d ) when addressed with d and said interpolation signal, where
space="preserve" listing-type="equation">s(t,d )=A cos [ω
.sub.c t+θ
(t,d )],and where A=amplitude, and ω
c =2π
fc ; andmeans for converting s(t,d ) into s(t). - View Dependent Claims (24, 25)
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26. A digital quadrature modulator for generating a continuous-phase frequency-shift keyed (CPFSK) signal having a modulation index of 0.5 comprising:
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a formatting circuit comprising; an L-bit serial-to-parallel shift register into which a serial data signal is clocked at a bit rate 1/T, and which generates an L-bit parallel data signal representative of said serial data signal; a 2-bit up/down binary counter, clocked at the bit rate 1/T, having its up/down counter control determined by the most significant bit of said parallel data signal, thereby providing a 2-bit phase state signal; a log2 M-bit counter, clocked at M times the bit rate 1/T, which generates a log2 M-bit data interpolation signal representative of the binary state of said log2 M-bit counter; a memory circuit comprising; a memory device having B2.sup.(L+log.sbsp.2M+2) storage locations, having address lines coupled to said parallel data signal, said phase state signal, and said data interpolation signal, having a B-bit output, and having stored therein representations of CPFSK signal data with a modulation index of 0.5 at a carrier frequency of J/MT where J<
M/2, and J and M are integers. - View Dependent Claims (27, 28)
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29. A method for generating a continuous-phase frequency-shift keyed (CPFSK) signal by quadrature modulating a radio frequency (RF) carrier with a digital input signal utilizing entirely digital techniques, said method comprising the steps of:
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translating serial input data having a predetermined bit rate into parallel input data; determining the phase quadrant of said serial input data in response to said bit rate and said parallel input data, thereby providing a phase control signal; interpolating between data bits of said serial input data, thereby providing an interpolation signal; addressing a memory utilizing said parallel input data, said phase control signal, and said interpolation signal; outputting a digital representation of a CPFSK signal from said memory; and
converting said digital representation into an analog CPFSK output signal having a precise modulation index. - View Dependent Claims (30, 31, 32, 33)
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34. A method for generating a continuous-phase frequency-shift keyed (CPFSK) signal s(t) by a quadrature modulating a radio frequency (RF) carrier fc with a digital input signal d(t) utilizing entirely digital techniques, said method comprising the steps of:
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(a) providing a data vector d of length L in response to d(t), wherein d has a bit rate 1/T; (b) determining a phase parameter of d(t) in response to d , thereby providing a phase signal θ
(t,d );(c) providing an interpolation signal having a clock rate M/T; (d) addressing a digital memory with d , θ
(t,d ) and said interpolation signal; and(e) outputting s(t,d ) from said digital memory, wherein
space="preserve" listing-type="equation">s(t,d )=A cos [ω
.sub.c t+θ
(t,d )]and wherein A=amplitude and ω
c =2π
fc. - View Dependent Claims (35, 36, 37, 38)
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39. A method for modulating a radio frequency carrier fc with a digital input signal d(t), said method comprising the steps of:
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(a) providing a data vector d of length L in response to d(t), wherein d has a bit rate 1/T; (b) determining the phase quadrant of d(t) in response to d , thereby providing a phase signal ψ
(t,d );(c) providing an interpolation signal having a clock rate M/T; (d) calculating parameters s(t,d ) of s(t) according to the equation
space="preserve" listing-type="equation">s(t,d )=A cos (ω
.sub.c t+θ
(t,d )),where ##EQU14## and where A=amplitude, ω
c =2π
fc, h is the modulation index, and q(t) is the modulation phase pulse signal;(e) storing parameters s(t,d ) into a digital memory at address locations determined by d , ψ
(t,d ), and said interpolation signal; and(f) generating a modulated analog signal responsive to said stored parameters s(t,d ). - View Dependent Claims (40)
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41. A method for quadrature modulation of a radio frequency (RF) carrier fc with an input signal d(t), said method comprising the steps of:
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(a) sampling the input signal d(t) at a sample rate 1/T, thereby creating a sampled data signal d(n) of length L; (b) defining parameters of a first signal I(t,d(n)) from said sampled data signal d(n); (c) defining parameters of a second signal Q(t,d(n)) from said sampled data signal d(n), wherein Q(t,d(n)) is in phase quadrature with I(t,d(n)); calculating parameters of modulated signal Imod(t,d(n)) by multiplying I(t,d(n)) by cos(.sup.ω
.sbsp.c (t)), where .sup.ω
.sbsp.c =2π
fc ;(e) calculating parameters of modulated signal Qmod.sup.(t,d(n)) by multiplying Q(t,d(n)) by sin(.sup.ω
.sbsp.c (t));(f) calculating parameters of a continuous-phase frequency shift keyed (CPFSK) signal s(t,d(n)) by subtracting Qmod.sup.(t,d(n)) from Imod .sup.(t,d(n)) ; (g) storing parameters of said CPFSK signal s(t,d(n)) into a digital memory; and (h) generating an analog signal responsive to said stored parameters of said CPFSK signal s(t,d(n)).
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42. A radio transmitter comprising:
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means for providing a bit clock signal having a predetermined bit rate; means for providing serial input data having said bit rate;
means for translating said serial input data into parallel input data;first memory means for storing data and for providing a digital representation of in-phase (I) and quadrature-phase (Q) component data signals in response to said parallel input data; means for providing a digital carrier signal representative of an integer multiple of said bit clock signal; second memory means for storing data and for providing a digital representation of in-phase (I) and quadrature-phase (Q) component carrier signals in response to said digital carrier signal; means, including said second memory means, for digitally modulating said I and Q carrier signals by said I and Q data signals, said second memory means further comprising means for storing data and for providing said digital quadrature modulating signal in response to said I and Q carrier signals and said I and Q data signals, thereby providing I and Q digital component signals; means, including said second memory means, for combining said I and Q digital component signals, thereby providing a digital quadrature modulated signal; means for converting said digital quadrature modulated signal into an analog output signal; and means for transmitting said analog output signal. - View Dependent Claims (43, 44, 45, 46, 47, 48)
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Specification