CN102916703A - 1-bit digital-to-analogue conversion and switch capacitor filtering circuit - Google Patents

Abstract

The invention discloses a 1-bit digital-to-analog conversion and switch capacitor filtering circuit, comprising an operational amplifier (13), a feedback capacitor (12) coupled between the negative input end and the output of the operational amplifier, a first sampling capacitor (11), a second sampling capacitor (10), and a switching change-over device used for charging and discharging the feedback capacitor and the sampling capacitors; in the charging process, the first sides of the first sampling capacitor (11) and the second sampling capacitor (10) are coupled to the voltage drain drain (VDD) or GND by the change-over device, and the second sides of the first sampling capacitor (11) and the second sampling capacitor (10) are coupled to voltage reference Vcm; and in the holding process, the first sampling capacitor (11) and the second sampling capacitor (10) are coupled to the feedback capacitor (12) by the change-over device. The 1-bit digital-to-analogue conversion and switch capacitor filtering circuit has the digital-to-analog conversion function and also has the low-pass filtering function.

Description

A kind of 1 figure place mould conversion and switch-capacitor filtering circuit

Technical field

The present invention is mainly concerned with the switching capacity digital to analog converter, and especially but not exclusively relate to 1 figure place mould conversion and the switch-capacitor filtering circuit that is applied to digital audio and video signals.

Background technology

In the past, digital to analog converter is mainly used in the fields such as data acquisition system, industrial process control, measurement and analysis.But enter after 21st century, digital technology begins to enter audio frequency and video field, particularly CD, VCD, DVD and home theater and enters common people house, and various portable music player (MP3, MD) more young man are favored; Radio digital communication (such as mobile phone) develops rapidly, and digital camera replaces traditional camera fully, and the vehicle-mounted digital sound equipment also constantly increases.In a word, fast development and the application of digital technology are more and more wider so that d convertor circuit also corresponding acquisition develop faster and progress.

Why these audio electronics products are in short so swift and violent spreading speed that occurs during the decade, and main cause is that their output tonequality is become better and better, price is more and more lower, volume is more and more less, the flying power of product is more and more stronger.These all give the credit to improving constantly of audio signal processing technique and integrated circuit technology level.Simultaneously, the active responding in market has promoted again further developing of audio signal processing technique conversely, makes it to become the study hotspot of this several years integrated circuit fields.

The required precision of field of audio processing logarithmic mode transducer is relatively high, exports in order to guarantee that audio signal is real high-qualityly, usually requires to reach the effective accuracy more than 16.The digital to analog converter of 1v for the outputting analog signal full scale, if want to realize 16 precision, the voltage that 1LSB is corresponding is 1/2^16=15 μ V, so require the aanalogvoltage of digital to analog converter output and the deviation of ideal value can not surpass 7.5 μ V, if do not adopt expensive laser-adjusting or other modification method, if this precision adopts the digital-to-analog converter structures of traditional type just can't realize at all.

Σ Δ (Sigma-Delta) technology has solved this problem, not only can realize the high accuracy conversion, but also do not need the analogue device of exact matching, thereby be best suited for the digital to analog converter implementation of digital audio application, it is so that the more convergence perfection of the audio signal quality of output, simultaneously also having reduced cost and power consumption, is the primary technology that realizes at present the high accuracy data conversion.

Fig. 1 has shown wherein a kind of d convertor circuit of the Σ of employing Δ technology, be input as the digital audio and video signals that 16 bit frequencies are fs, after interpolation filter and sigma Delta modulator, becoming 1 bit frequency is the high-frequency digital audio signal of N*fs, and then realize the function (DAC) of digital to analogy conversion through the change-over circuit between the digital to analogy, more common mode is to adopt the switching capacity change-over circuit, signal after the switching capacity change-over circuit is processed is continuous in amplitude, but still disperse in time, therefore also need to connect an analog reconstruction filter in switching capacity change-over circuit back, remove high-frequency noise, reduce real simulated audio signal.

Switching capacity DAC adopts " directly electric charge shifts " digital-to-analogue conversion structure, as shown in Figure 2, and at phase place Φ 1 period of contact, sampling capacitance C ₁Digital signal S according to input ₁Value charge or discharge, at phase place Φ 2 periods of contact, sampling capacitance C ₁With feedback capacity C _FBBe parallel to the input/output terminal of operational amplifier, sampling capacitance C ₁With feedback capacity C _FBBetween electric charge occurs shifts, realize the function of digital to analogy conversion, amplifier need not to provide drive current in this structure, so power consumption reduces greatly.

Summary of the invention

An object of the present invention is to provide a kind of conversion of 1 figure place mould and switch-capacitor filtering circuit that is applied to digital audio and video signals, described digital-to-analogue conversion also has the low-pass filtering function except having the translation function between the digital to analogy.

Above-mentioned purpose is realized by following technical scheme:

A kind of 1 figure place mould conversion and switch-capacitor filtering circuit, it is characterized in that: comprise an operational amplifier 13, be coupling in the feedback condenser 12 between the input and output of operational amplifier negative pole, the first sampling capacitor 11, the second sampling capacitor 10, and be used for switching device that feedback capacity and sampling capacitance are discharged and recharged; Described switching device shifter is coupled to the first side of the first sampling capacitor 11 and the second sampling capacitor 10 supply voltage VDD or ground GND between charge period, the second side of the first sampling capacitor 11 and the second sampling capacitor 10 is coupled to reference voltage Vcm; Described switching device shifter is coupled to described feedback condenser 12 with the first sampling capacitor 11 and the second sampling capacitor 10 during keeping.

Description of drawings

Fig. 1 is the d convertor circuit schematic diagram of the applied a kind of Σ of the employing Δ technology of the present invention;

Fig. 2 is a kind of 1 figure place mould conversion and switch-capacitor filtering circuit diagram proposed by the invention;

Fig. 3 is the schematic diagram of the difference implementation of circuit proposed by the invention;

Embodiment

Below with reference to the drawings and specific embodiments the present invention is described in further details.

Fig. 1 is the d convertor circuit schematic diagram of the applied a kind of Σ of the employing Δ technology of the present invention, be input as the digital audio and video signals that 16 bit frequencies are fs, after interpolation filter and sigma Delta modulator, becoming 1 bit frequency is the high-frequency digital audio signal of N*fs, and then realize the function (DAC) of digital to analogy conversion through the change-over circuit between the digital to analogy, more common mode is to adopt the switching capacity change-over circuit, signal after the switching capacity change-over circuit is processed is continuous in amplitude, but still disperse in time, therefore also need to connect an analog reconstruction filter in switching capacity change-over circuit back, remove high-frequency noise, reduce real simulated audio signal.

Fig. 2 is a kind of 1 figure place mould conversion and switch-capacitor filtering circuit diagram proposed by the invention, comprise an operational amplifier 13, be coupling in the feedback condenser 12 between the input and output of operational amplifier negative pole, the first sampling capacitor 11, the second sampling capacitor 10, and be used for switching device that feedback capacity and sampling capacitance are discharged and recharged; Described switching device shifter is coupled to the first side of the first sampling capacitor 11 and the second sampling capacitor 10 supply voltage VDD or ground GND between charge period, the second side of the first sampling capacitor 11 and the second sampling capacitor 10 is coupled to the 3rd reference voltage Vcm; Described switching device shifter is coupled to described feedback condenser 12 with the first sampling capacitor 11 and the second sampling capacitor 10 during keeping.

With reference to shown in Figure 2, at phase place Φ 1 period of contact, the first sampling capacitor 11 and the second sampling capacitor 10 are according to the digital signal S of input ₁Value charge or discharge, at phase place Φ 2 periods of contact, the first sampling capacitor 11 and the second sampling capacitor 10 are parallel to the input/output terminal of operational amplifier, sampling capacitance C with feedback condenser 12 ₁With feedback capacity C _FBBetween electric charge occurs shifts, realize the function of digital to analogy conversion, amplifier need not to provide drive current in this structure, so power consumption reduces greatly.

With reference to circuit shown in Figure 2, its transfer function can be calculated as:

During Φ 1 closure, total electrical charge is:

Q _Φ1=S(n)*C ₁+S(n-1)*C ₁

=(1+z ^-1)*C ₁*S(z)

During Φ 2 closure, because C _FBThere is not discharge process, C _FBOn accumulated last time total electrical charge, and C ₁And C _FBRelation in parallel, so total electrical charge becomes:

Q _Φ2=(2C ₁+C _FB)*V(n)-C _FB*V(n+1)

=(2C ₁+C _FB-C _FB*z)*V(z)

Therefore have: $H\left(z\right)=\frac{V\left(z\right)}{S\left(z\right)}=\frac{(1+z^{-1})*C_1}{(2C_1+C_{\mathrm{FB}}-C_{\mathrm{FB}}*z)}=\frac{1/2(1+z^{-1})}{1+C_{\mathrm{FB}}/2C_1-(C_{\mathrm{FB}}/2C_1)*z^{-1}}$

From transfer function, can find out, a kind of 1 figure place mould conversion proposed by the invention and switch-capacitor filtering circuit not only have the translation function between the digital to analogy, the function that also has simultaneously single order switching capacity low-pass filtering (SC LPF) and single order finite impulse response (FIR) filtering, improve the ability of the anti-clock jitter of circuit, effectively improved the signal to noise ratio of output signal.

Fig. 3 is the schematic diagram of the difference implementation of Fig. 2 circuit, and operation principle is identical with Fig. 2, no longer describes in detail here.

The above has done detailed description to embodiments of the invention by reference to the accompanying drawings, but the present invention is not limited to above-described embodiment, in the ken that those of ordinary skills possess, can also make a variety of changes under the prerequisite that does not break away from aim of the present invention.The quantity that for example increases switching capacity among Fig. 2 can realize the more digital-to-analogue conversion of seniority top digit, and the quantity that for example increases again register among Fig. 3 can realize the FIR filter function of higher exponent number.

Claims (8)

1. a figure place mould is changed and the switch-capacitor filtering circuit, it is characterized in that: comprise an operational amplifier (13), be coupling in the feedback condenser (12) between operational amplifier negative input end and the output, the first sampling capacitor (11), the second sampling capacitor (10), and be used for switching device that feedback capacity and sampling capacitance are discharged and recharged; Described switching device shifter is coupled to the first side of the first sampling capacitor (11) and the second sampling capacitor (10) supply voltage VDD or ground GND between charge period, the second side of the first sampling capacitor (11) and the second sampling capacitor (10) is coupled to reference voltage Vcm; Described switching device shifter is coupled to described feedback condenser (12) with the first sampling capacitor (11) and the second sampling capacitor (10) during keeping.

2. a kind of 1 figure place mould according to claim 1 is changed and the switch-capacitor filtering circuit, and wherein said operational amplifier is difference input Single-end output, and its positive input terminal links to each other with reference voltage Vcm.

3. a kind of 1 figure place mould according to claim 1 is changed and the switch-capacitor filtering circuit, and wherein said switching device is by the digital signal S of input ₁, S ₂Come co-controlling closed or open with clock signal Φ 1, Φ 2.

4. a kind of 1 figure place mould conversion according to claim 1 and switch-capacitor filtering circuit are closed when wherein said switching device can be set to high level, so that the signal transmission pathway conducting opens during low level, so that signal transmission pathway is cut off.

5. a kind of 1 figure place mould according to claim 3 is changed and the switch-capacitor filtering circuit wherein said supplied with digital signal S ₁The binary bit stream of Sigma-Delta modulator output, described supplied with digital signal S ₂Supplied with digital signal S ₁Through the output of a register delay after clock cycle.

6. a kind of 1 figure place mould according to claim 3 is changed and the switch-capacitor filtering circuit, and wherein said clock signal Φ 1 and Φ 2 are the non-overlapping clock of two-phase under the same frequency.

7. a kind of 1 figure place mould according to claim 1 is changed and the switch-capacitor filtering circuit, and the appearance value of the appearance value of wherein said the first sampling capacitor (11) and the second sampling capacitor (10) equates.

8. a kind of 1 figure place mould according to claim 1 is changed and the switch-capacitor filtering circuit, and the transfer function of wherein said switch-capacitor filtering circuit is:

, C wherein ₁Be the appearance value of the first sampling capacitor (11) and the second sampling capacitor (10), C _FBAppearance value for feedback condenser (12).

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