Digital sweep type spectrum analyzer with up/down frequency conversion

Patent metadata

Field	Value
Publication number	US-9759753-B2
Application number	US-201414654881-A
Country	US
Kind code	B2
Filing date	Nov 18, 2014
Priority date	Nov 18, 2014
Publication date	Sep 12, 2017
Grant date	Sep 12, 2017

Abstract

System for digital sweep type spectrum analysis with up/down frequency provides measurements of frequency spectrum of complex analog baseband input signal. The signal is quantized into three levels with fs based on the bandwidth of the input signal. Four multiplexers, a first block of registers and a block of adders perform operations equivalent to complex multiplication of the quadrature components. Two complex signals with up and down shifted spectrum are produced by the adders. The quadrature components are inputted to the accumulators with reset, which act as low-pass filters and accumulate several samples at a constant frequency f LO of the local oscillator. Levels of two accumulated complex samples are estimates of input signal spectrum in two frequency points +f LO and −f LO . A sweep controller changes a frequency of the local oscillator from zero up to fs/2. Estimates of the input signal spectrum are generated sequentially in range −fs/2 to +fs/2.

First claim

What is claimed is:

1. A digital sweep type spectrum analyzer with up/down frequency conversion, which provides a frequency spectrum of a complex analog input signal, the analyzer comprising:
(i) two three-level analog-to-digital converters (ADC), whose inputs are analog quadrature components I a (t), Q a (t) of the complex input signal and whose digital quadrature output (I ADC , Q ADC ) is quantized into three levels (−1; 0; +1),
wherein an ADC sampling frequency fs corresponds to a bandwidth B in of the complex input signal (fs≧B in );

(ii) a quadrature local oscillator (LO), which generates a digital complex sinusoid with quadrature components (I LO , Q LO ) based on a sweep signal at its frequency control input;
(iii) a MUX block comprising four 9-to-1 multiplexers MUX 1, MUX 2, MUX 3, MUX 4 whose selected inputs are connected to the outputs of the first and second ADC and whose data inputs connected to the quadrature components (I LO , Q LO ), wherein the MUX block generates, without using multiplication, real numbers as follows:
R II =I ADC *I LO ,
R QQ =Q ADC *Q LO ,
R IQ =I ADC *Q LO ,
R QI =Q ADC *I LO ;
wherein the four 9-to-1 multiplexers MUX 1, MUX 2, MUX 3, MUX 4 operate as follows:

Outputs

Select inputs
MUX 1
MUX 2
MUX 3
MUX 4

I ADC
Q ADC
R II
R QQ
R IQ
R QI

1)
0
0
0
0
0
0

2)
0
+1
0
 Q LO
0
 I LO

3)
0
−1
0
−Q LO
0
−I LO

4)
+1
0
 I LO
0
 Q LO
0

5)
−1
0
−I LO
0
−Q LO
0

6)
+1
+1
 I LO
 Q LO
 Q LO
 I LO

7)
−1
−1
−I LO
−Q LO
−Q LO
−I LO

8)
+1
−1
 I LO
−Q LO
 Q LO
−I LO

9)
−1
+1
−I LO
 Q LO
−Q LO
 I LO

(iv) a first block of registers comprising four registers connected to respective outputs of the MUX block;
(v) a block of adders comprising four adders, whose inputs are connected to registers of the first block of registers,
wherein the block of adders produces a complex up-converted signal with quadrature components (I U , Q U ) and a complex down-converted signal with quadrature components (I D , Q D ) as follows:
I U =R II −R QQ ,
Q U =R IQ +R QI ,
I D =R II +R QQ ,
Q D =−R IQ +R QI ;

(vi) a second block of registers comprising four registers;
(vii) a block of accumulators comprising four accumulators whose inputs are fed from the outputs of the block of adders,
wherein every accumulator accumulates M samples (M>>1) respectively I U , Q U , I D , Q D at a constant frequency of the LO, then the resulting values I m U,A , Q m U,A , I m D,A , Q m D,A are divided by a coefficient 2 K (2 K ≦M) by shifting by K bits toward a least significant bit (LSB) and resulting values I m U,K , Q m U,K , I m D,K , Q m D,K are written into the four registers of the second block of registers, then all four accumulators are reset to zero and the process is repeated for the next frequency of the LO;

(viii) a level detector that estimates vector levels V U and V D with complex quadrature samples (I U,K , Q U,K ) and (I D,K , Q D,K ) respectively of the second block of registers, wherein the level V U is an estimate of the input signal spectrum at a frequency point −f LO and the level V D is an estimate of the input signal spectrum at a frequency point +f LO ;
(ix) a data analysis and collection logic that receives spectrum data from the level detector, analyzes the spectrum data and sequentially stores the spectrum data within one scanning period, after which the spectrum data is updated;
(x) a sweep and data collection controller that sends a sweep signal to frequency control input of the LO to control the LO by a stepwise change of frequency in a range (0, +fs/2), sequentially setting N>>1 of equidistant frequency values fn=fs*(2n−1)/4N, where n=1, 2, . . . , N,
wherein each accumulator of the block of accumulators accumulates M samples at each frequency fn: M=floor[k*N], where constant k is selected from a range (0.5, . . . , 5.0),
wherein the spectrum analyzer forms 2N spectrum points in a range (−fs/2, +fs/2) during each sweep period.

2. The digital spectrum analyzer of claim 1 , wherein the data analysis and collection logic analyzes the spectrum data to detect presence of narrowband interference frequencies for interference rejection.

3. The digital spectrum analyzer of claim 1 , wherein the level detector produces a rough estimate of vector length for each input vector using the following successive steps:
d) forming auxiliary vector with orthogonal components (X, Y), where X=max(|x|, |y|), Y=min(|x|, |y|), x, y—orthogonal components of the input vector, wherein the auxiliary vector is located in the (0, π/4) octant;
e) finding in the (0, π/4) octant a preset sector, which contains the auxiliary vector;
f) selecting a linear equation corresponding to the found sector; and
g) solving the linear equation with preset coefficients.

4. The digital spectrum analyzer of claim 1

Assignees

• Topcon Positioning Systems Inc

Inventors

• Veitsel Andrey V
• Prasolov Victor A
• Murzinov Dmitry D
• Orlovsky Igor A

Classifications

• G01R23/173 Primary

  Wobbulating devices similar to swept panoramic receivers · CPC title

• G01R23/16 Primary

  Spectrum analysis; Fourier analysis · CPC title