CN104218949B - A kind of digital Deltasigma modulator structure suitable for fractional synthesizer - Google Patents
A kind of digital Deltasigma modulator structure suitable for fractional synthesizer Download PDFInfo
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Abstract
The invention discloses a kind of digital Deltasigma modulator structure suitable for fractional synthesizer, including first order error feedback-type modulator, feedback path, second level error feedback-type modulator and error counteracting module；Difference between the output of feedback path and the output of first order modulator obtains the output of feedback path after delay cell；Input signal by noise suppressed enhancement unit and after filtering between value and the output of feedback path between the disturbing signal after processing unit and it is worth the input as first order error feedback-type modulator；First order error feedback signal as second level error feedback-type modulator input；The output of first order error feedback-type modulator obtains the output of whole modulator with the output of second level error feedback-type modulator after error counteracting module.Present invention introduces feedback control loop, the number that higher-order noise suppresses, reduced output quantization level is realized, design of integer electro-circuit complexity and power consumption is reduced.
Description
Technical field
The present invention relates to belong to technical field of integrated circuits, more particularly to a kind of number suitable for fractional-type frequency synthesizer
Word Deltasigma modulator structure.
Background technology
Modern wireless communication develop rapidly cause wireless communication system for frequency synthesizer frequency accuracy and frequency
Switching time proposes higher requirement.Want to obtain smaller setup time, then require that phaselocked loop has wide loop bandwidth.
The mutual constraint between frequency accuracy, frequency switching time, phase noise is there is in integral frequency divisioil frequency synthesizer, it is difficult to
Meet the requirement in Modern Communication System.For fractional-type frequency synthesizer, because its output frequency can be the small of reference frequency
Several times, so higher reference frequency and larger loop bandwidth can be used, so as to reduce frequency switching time, take into account
The requirement of each side such as phase noise, frequency accuracy, lock speed, widely should have been obtained in twireless radio-frequency communication chip
With.But fractional synthesizer have the shortcomings that one it is very serious, i.e., can introduce fractional stray.For this shortcoming mesh
Before propose a variety of solutions, most common of which is exactly using Deltasigma modulator technology.Can be fine so design is a
Ground suppresses the Deltasigma modulator of fractional stray, is of great significance for the improvement tool of frequency synthesizer performance.At present, should
Modulator for frequency synthesizer uses three rank MASH Deltasigma modulator structures mostly.But the output of this structure up to 8
Individual quantization level, greatly improves the linearity to phase frequency detector, charge pump and frequency divider in frequency synthesizer system
It is required that, add complex circuit designs degree and power consumption.Therefore, in the case where identical fractional stray inhibition can be reached, subtract
Small output quantization level is significant.
The content of the invention
The technical problem to be solved：In view of the shortcomings of the prior art, the present invention proposes a kind of fractional frequency that is applied to and closed
The digital Deltasigma modulator structure grown up to be a useful person, solve existing three ranks MASH Deltasigma modulators structure need to design complicated circuit and
The high technical problem of power consumption.
Technical scheme：In order to solve the above technical problems, the present invention uses following technical scheme：
A kind of digital Deltasigma modulator structure suitable for fractional synthesizer, including the modulation of first order error feedback-type
Device, feedback path, second level error feedback-type modulator and error counteracting module；
The output C (z) of the feedback path and output Y of first order modulator1(z) difference between is obtained after delay cell
To the output C (z) of feedback path；
Disturbance after noise suppressed enhancement unit G (z) input signal X (z) and processing unit D (z) after filtering
Between signal and value X1(z) between the output C (z) of feedback path and value be used as first order error feedback-type modulator
Input；
First order error feedback signal e1(z) as the input of second level error feedback-type modulator；
The output Y of first order error feedback-type modulator1(z) with the output Y of second level error feedback-type modulator2(z) pass through
Cross the output Y (z) that whole modulator is obtained after error counteracting module.
Feedback path is introduced in the present invention by the defeated of the i.e. first order error feedback-type modulator of the output signal after quantization
Go out Y1(z) input of first order error feedback-type modulator is fed back to, except normal noise suppression effect can be realized also
Single order noise shaping can be increased, i.e., the noise shaping effect of higher order is realized under the exponent number of identical Deltasigma modulator, is
This reduces the output quantization number of levels of half.
Further, in the present invention, the input of the first order error feedback-type modulator is with passing through delay cell
First error feedback signal e1(z) between and value is V1(z), the output Y of first order modulator1(z) it is V1And the first order (z)
The quantizing noise E of error feedback-type modulator1(z) between and value, the first error feedback signal e1(z) it is V1(z) with the
The output Y of one-level error feedback-type modulator1(z) difference between.
Further, in the present invention, the input of the second level error feedback-type modulator is with passing through delay cell
Second error feedback signal e2(z) between and value is V2(z), the output Y of second level modulator1(z) it is V2And the second level (z)
The quantizing noise E of error feedback-type modulator2(z) between and value, the second error feedback signal e2(z) it is V2(z) with the
The output Y of two grades of error feedback-type modulators2(z) difference between.
Further, in the present invention, the output Y of the first order error feedback-type modulator1(z) with second level error
The output Y of feedback-type modulator2(z) as two inputs of error counteracting module, wherein second level error feedback-type modulator
Output Y2(z) output Y successively after two rank filtering unit filters with first order error feedback-type modulator1(z) make and,
Obtain and value as error counteracting module output.
Further, in the present invention, the Z-domain transfer function of the noise suppressed enhancement unit is G (z)=(1-z-1
)-1, the introducing of the unit plays the enhanced effect of noise suppressed.
Further, in the present invention, the Z-domain transfer function of the delay cell is z-1, it, which is acted on, causes error feedback
Signal, which is delayed under the control of clock after a cycle, to be fed back to input and carries out computing.
Further, in the present invention, the Z-domain transfer function of the filter unit is 1-z-1, the introducing of the filter unit
Serve the effect of reduction noise floor.
Beneficial effect：A kind of Deltasigma modulator structure suitable for fractional-type frequency synthesizer that the present invention is provided, is being passed
Unite on the basis of modulator, introduce feedback control loop, compare and had the following advantages that with traditional digital Deltasigma modulator：
Firstth, digital Deltasigma modulator of the invention cascades for single order, has accomplished, in the case where not cascading many exponent numbers, to reach
To the noise shaping effect of higher order modulation device, area and power consumption are saved compared to higher order modulator；
Secondth, digital Deltasigma modulator of the invention reduces the output quantization number of levels of half, has decoupled modulator
Exponent number with to system linear degree requirement contradiction, during applied to fractional-type frequency synthesizer, reduce output signal of frequency divider
With the instantaneous phase error of reference signal, subtract and reduce in frequency synthesizer system to phase frequency detector, charge pump and frequency dividing
The linearity of device, reduces design of integer electro-circuit complexity and power consumption.
Brief description of the drawings
Fig. 1 is structural representation of the invention；
Fig. 2 is the power spectral density of output signal of the present invention；
Fig. 3 is the distribution map of output quantization level of the present invention.
Embodiment
The present invention is further described below in conjunction with the accompanying drawings.
It is a kind of digital Deltasigma modulator knot suitable for fractional-type frequency synthesizer proposed by the invention as shown in Figure 1
Structure, it is main to include traditional error feedback-type modulator of two single order cascades, respectively first order error feedback-type modulator
What second level error feedback-type modulator, and feedback path, error counteracting module.Wherein feedback path is located at most upper in Fig. 1
In the dotted line frame of side, two dotted line frames below feedback path are respectively first order error feedback-type modulator and second level error
It is error counteracting module in dotted line frame on the right side of feedback-type modulator, Fig. 1.Input signal X (z) passes through noise suppressed enhancement unit
X is obtained after G (z) processing and addition disturbing signal1(z), X1(z) the output signal C (z) with feedback path is together as the first rank
The input of error feedback-type modulator, obtains exporting Y by first order error feedback-type modulator1(z).First order error is fed back
Signal e1(z) as the input signal of second level error feedback-type modulator, obtained by second level error feedback-type modulator
Export Y2(z).In figure, E1(z) it is quantizing noise that the quantizer in first order error feedback-type modulator is introduced, E2(z) it is
The quantizing noise that quantizer in two grades of error feedback-type modulators is introduced.By the way that two rank (1-z will be passed through-1) second level after filtering
The output Y of modulator2(z) with the output Y of first order modulator1(z) addition is realized as the output Y (z) of whole modulator
Error counteracting.
Summation in said process, difference is asked to be realized by accumulator.
The noise transmission function (Noise Transfer Function, abbreviation NTF) and signal of total are passed below
Defeated function (Single Transfer Function, abbreviation STF) is derived：
Known Y (z)=STF (z) X (z)+NTF (z) E (z)
It can be obtained by Fig. 1：
Y1(z)=V (z)+E1(z)
e1(z)=V (z)-Y1(z)
X1(z)=X (z) * G (z)
Again due to G (z)=(1-z-1)-1
e1(z)=- E1(z)
Y1(z)=X (z)+(1-z-1)2E1(z)
Y2(z)=e1(z)+(1-z-1)E2(z)
Comprehensive above equation can be obtained：
Y (z)=Y1(z)+(1-z-1)2Y2(z)=X (z)+(1-z-1)3E2(z)
So as to obtain：
Signal transfer function：STF (z)=1
Noise transfer function：NTF (z)=(1-z-1)3
From NTF, Deltasigma modulator structure of the invention realizes the noise shaping effect of three ranks, compared to traditional Δ
Sigma modulator, improves single order noise inhibiting ability.
Specifically, setting the bit wide of accumulator as 16bit, thus selectivity constant 0.5 obtains Fig. 2's as input signal
The power spectrum density of output signal and Fig. 3 output quantization level distribution figure.From fig. 2 it can be seen that proposed by the invention
Structure have three ranks shaping effect and good spectral performance, from figure 3, it can be seen that output only have 4 quantization levels,
Reduce " instantaneous phase error " of the frequency synthesizer in lock-out state, therefore can frequency and phase discrimination significantly in alleviation system
The requirement of the linearities such as device, charge pump and frequency divider, so as to reduce the complexity of circuit design, also reduces the work(of system
Consumption.
Described above is only the preferred embodiment of the present invention, it should be pointed out that：For the ordinary skill people of the art
For member, under the premise without departing from the principles of the invention, some improvements and modifications can also be made, these improvements and modifications also should
It is considered as protection scope of the present invention.
Claims (7)
1. a kind of digital Deltasigma modulator structure suitable for fractional synthesizer, it is characterised in that：Including first order error
Feedback-type modulator, feedback path, second level error feedback-type modulator and error counteracting module；
The output C (z) of the feedback path and output Y of first order error feedback-type modulator1(z) difference between is single by delay
The output C (z) of feedback path is obtained after member；
Disturbing signal after noise suppressed enhancement unit G (z) input signal X (z) and processing unit D (z) after filtering
Between and value X1(z) between the output C (z) of feedback path and value be used as the defeated of first order error feedback-type modulator
Enter；
First order error feedback signal e1(z) as the input of second level error feedback-type modulator；
The output Y of first order error feedback-type modulator1(z) with the output Y of second level error feedback-type modulator2(z) by missing
The output Y (z) of whole modulator is obtained after poor cancellation module.
2. the digital Deltasigma modulator structure according to claim 1 suitable for fractional synthesizer, it is characterised in that：
The input of the first order error feedback-type modulator and the first error feedback signal e Jing Guo delay cell1(z) sum between
It is worth for V1(z), the output Y of first order error feedback-type modulator1(z) it is V1(z) with the amount of first order error feedback-type modulator
Change noise E1(z) between and value, the first error feedback signal e1(z) it is V1(z) with first order error feedback-type modulator
Output Y1(z) difference between.
3. the digital Deltasigma modulator structure according to claim 1 suitable for fractional synthesizer, it is characterised in that：
The input of the second level error feedback-type modulator and the second error feedback signal e Jing Guo delay cell2(z) sum between
It is worth for V2(z), the output Y of second level error feedback-type modulator1(z) it is V2(z) with the amount of second level error feedback-type modulator
Change noise E2(z) between and value, the second error feedback signal e2(z) it is V2(z) with second level error feedback-type modulator
Output Y2(z) difference between.
4. the digital Deltasigma modulator structure according to claim 1 suitable for fractional synthesizer, it is characterised in that：
The output Y of the first order error feedback-type modulator1(z) with the output Y of second level error feedback-type modulator2(z) as mistake
Two inputs of poor cancellation module, wherein the output Y of second level error feedback-type modulator2(z) successively list is filtered by two ranks
Output Y after member filtering with first order error feedback-type modulator1(z) make and, obtain and value as error counteracting module
Output.
5. the digital Deltasigma modulator knot as claimed in any of claims 1 to 4 suitable for fractional synthesizer
Structure, it is characterised in that：The Z-domain transfer function of the noise suppressed enhancement unit is G (z)=(1-z-1)-1, z domain of definition for (-
∞, 0) ∪ (0 ,+∞).
6. the digital Deltasigma modulator knot as claimed in any of claims 1 to 4 suitable for fractional synthesizer
Structure, it is characterised in that：The Z-domain transfer function of the delay cell is z-1, z domain of definition is (- ∞, 0) ∪ (0 ,+∞).
7. the digital Deltasigma modulator structure according to claim 4 suitable for fractional synthesizer, it is characterised in that：
The Z-domain transfer function of the filter unit is 1-z-1, z domain of definition is (- ∞, 0) ∪ (0 ,+∞).
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US7741918B1 (en) * | 2005-06-30 | 2010-06-22 | Cypress Semiconductor Corporation | System and method for an enhanced noise shaping for spread spectrum modulation |
| CN102394654A (en) * | 2011-10-10 | 2012-03-28 | 电子科技大学 | Delta-sigma modulator applicable to decimal frequency division |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US7741918B1 (en) * | 2005-06-30 | 2010-06-22 | Cypress Semiconductor Corporation | System and method for an enhanced noise shaping for spread spectrum modulation |
| CN102394654A (en) * | 2011-10-10 | 2012-03-28 | 电子科技大学 | Delta-sigma modulator applicable to decimal frequency division |
Non-Patent Citations (1)
| Title |
|---|
| 频率合成器中∑-Δ调制器的设计与实现;刘德建;《计算机工程与科学》;20091231;第31卷(第12期);第121-123页 * |
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