JPH09238078A - D/a converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the D/A converter suitable for circuit integration in which the utilizing efficiency of energy of a current source is improved through differential processing, the dynamic range is increased. SOLUTION: Each of current sources S1 -SN is connected to a 1st current sink P1 or a 2nd current sink P2 via relating switches I11 , I21 ,...I1 N, I2 N, a differential amplifier A2 converts a difference between a current activated by a converted digital signal and led out from the current sources and a current absorbed by the current sinks P1 , P2 into a difference voltage relating to the converted digital signal. A prescribed value of the current led out from the current sources is absorbed by the current sinks P1 , P2 , and the differential amplifier A2 forms an active time filter to generate an analog signal being an output voltage of the converter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an analog converter, particularly a digital / analog converter using a current source.

[0002]

Generally, digital-to-analog converters that use current source solutions are of the unipolar type, which means that a portion of the current source network that is not used in the conversion process is grounded. Since it is tapped off, it loses up to 50% of its energy unused.

[0003]

SUMMARY OF THE INVENTION The present invention allows the functions described above to be integrated in a circuit, thus reducing the surface area of silicon used and is an improvement over known devices. A novel digital-to-analog converter (also referred to as DAC) architecture that can be obtained by using a current source is provided.

The subject of the invention is therefore a digital-to-analog converter, which converter comprises a current source, each of which comprises a first common current sink or a second common current sink and a current source. Associated with a switch to connect,
This converter also converts the difference between the current drawn by these current sources activated by the digital signal to be converted and the current absorbed by these current sinks into the digital signals listed above. A differential / differential amplifier for converting into a related differential voltage, and the above-mentioned first and second current sinks for absorbing a constant value of the current derived by the respective current source, which differential / differential The dynamic amplifier forms an active time filter, the output voltage of which forms the analog signal generated by the converter.

[0005]

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a possible embodiment of the known monopolar technique.

The circuit shown in FIG. 1 has N current sources S ₁
, S _N , each of these current sources being linked to ground via a first switch I _{11 to} I _1N and to a current sink P ₁ by a second switch I _{21 to} I _2N . There is.

The switches I ₁₁ , I ₂₁ , ... I _1N , I _2N are pair-coupled, so that when one switch is open, the other switch is closed and this relationship is transposed. These switches form a two position switch in a 2 × 2 fashion.

The switches I _{22 to} I _2N further include an amplifier A ₁
, The second input of the amplifier is linked to the voltage V _cm , while the output of the amplifier is the resistor R
Is linked to the first input of this amplifier.

The control terminals of the switches I _{11 to} I _1N and I _{21 to} I _2N are connected to the input for the digital code to be converted.

Depending on the n-bit nature of the applied digital code, the corresponding switch is turned on or off.

The current appearing at the first input of amplifier A ₁ is
Equal to (n-N / 2) I.

A current equal to (N / 2) I has a current sink P
_A current equal to (N−n) I, while flowing in ₁ , flows to ground through the connection of switches I ₁₁ -I _1N .

Then, the voltage V = V _cm is output to the output of the amplifier A _1.
-R * (n-N / 2) I appears, which is the analog output signal from this converter.

As a result of the operation of the circuit of FIG. 1, the current sources S _{1 to} S ₁
Some of the current derived by _N is lost during the digital-to-analog conversion.

FIG. 2 illustrates the placement of the circuit described with reference to FIG. 1 into differential mode.

The circuit shown in FIG. 2 is similar to that of FIG. 1, and thus the same components of these two circuits are labeled with the same reference numbers.

This circuit differs from that of FIG. 1 in that
Current sink P_TwoIs switch I₁₁, I _1NSeries connection and
Connected to a current sink P and a current sink P_TwoBut
Differential / differential amplifier A_TwoConnected to the negative input of
Touch I_{twenty one}~ I_2NCurrent sink P linked to₁But this increase
It is connected to the positive input of the width box.

A first resistor R ₁ is connected between the positive input of the amplifier A ₂ and the corresponding negative output, whereas a second resistor R ₂ of the same value as the resistor R ₁ is provided. It is connected between the negative input and the positive output of the amplifier.

Under these conditions, the current NI derived by the current sources S _{1 to} S _N is shunted into the current (N / 2) I flowing through each of the current sinks P ₁ and P ₂ .

The current (n-N / 2) I is supplied to the positive input of the amplifier A ₂ , whereas the current (N / 2-n) I is supplied to the negative input of this amplifier.

Then, the following voltage appears at the output of this amplifier.

[0022]

[Number 1] _{V- = V cm -R (n-} N / 2) I V + = V cm -R (N / 2-n) I and R is the value of resistor R _1, R _2.

As a result, the following voltage appears at the output terminal of this amplifier.

[0024]

## EQU00002 ## V _cm = V + -V-=-R (N-2n) I

The differential solution makes it possible to optimize the energy, and this solution offers the possibility to use a current source not used in the monopole design as an aid to the active circuit.

Whereas the used current source of the equivalent unipolar digital / analog converter produces one polarity of the difference signal, the unused current source of this digital / analog converter at one equivalent end is Generate the other polarity of the difference signal.

Furthermore, in order to reduce energy waste, the differential solution offers the following advantages:

1) Double the dynamic range of the converter, which means increasing the signal-to-noise ratio by 6 dB.

2) Convert stray signals (power supply noise, combined signal) into a common mode signal that does not disturb the difference signal.

The drawback of this solution is that it requires a current source with dual sinks.

According to the invention, this drawback is used to compensate the converter's osset voltage, as will be explained later.

Since analog signals are used most of the time in the form of voltage rather than in the form of current, current / voltage conversion is accomplished by injecting a differential current into a continuous active time filter, which filter. It reduces the high frequency signals generated during the sampling of the transducer.

As can be seen from the configuration of FIG. 2 described herein, a differential / differential amplifier in which a current source forming a second sink is added to the circuit of FIG. 1 and which has a differential input and a differential output. Is used. This repositioning has the advantage of doubling the output swing of the amplifier and therefore doubling the dynamic range of the converter. Increasing the signal to noise ratio by 6 dB is achieved without sacrificing energy.

In the unipolar solution (FIG. 1), amplifier A ₁ is
The common connection point between the current source and the current sink of the digital / analog converter is made to follow the common mode voltage V _cm applied to the positive terminal of this amplifier. In the differential solution, the amplifier A
₂ no longer has a common mode voltage reference terminal.

Additional amplifiers are required to control the common mode voltage at the positive and negative outputs of the digital to analog converter.

As shown in FIG. 3, an amplifier A ₃ having the characteristic of having two input stages is common to the current source of the digital / analog converter and the two current sinks P ₁ and P ₂ and Σ + and To evaluate the average value of the voltage applied to the Σ-connection point, compare this average value with the common mode voltage V _cm and keep the Σ + and Σ-connection points ideally at a potential equal to V _cm. , The bias signals of the current sinks P ₁ and P ₂ are controlled.

The voltage difference at Σ + and Σ− is the amplifier A ₂
Error in the mean value of the Σ + and Σ− voltages due to the non-linearity of amplifier A ₃ is also minimized by the feedback loop of amplifier A ₂ .

The disadvantages of adding a second current sink to the differential solution described above can be used to advantage in offset voltage compensation networks. Utilizing this dual current sink, an auxiliary digital-to-analog converter is obtained by using two current sinks, which makes it possible to compensate the offset voltage of the main converter.

FIG. 4 shows a method of converting two current sinks into an offset compensation auxiliary digital-to-analog converter.

The circuit of FIG. 4 is similar to that of FIG.

This circuit is different from FIG. 3 in that the current sink is
P₁, P_TwoInstead of directly controlling_ThreeOutput
The amplifier A_TwoThe negative and positive inputs of
Two current sinks P connected together like₁, P_TwoIncluding
Connect to the control terminals of several current sinks, and M
Current sink P formed by the₁₁~ P_1MSystem
Connect to the control terminal, current sink P₁₁~ P_1MIn this example
Is controlled by the offset digital code k
Paired auxiliary switch I₃₁~ I_3M, I₄₁~ I_4MBy
Via the changeover switch formed by
Itch I₁₁, I _1NAnd switch I_{twenty one}, I_2NConnection point and
It is connected with the source.

As a result of this connection arrangement, the combination of currents derived by the current sources S _{1 to} S _N is shunted between the above-mentioned current sinks as follows.

The current sink P ₁ carries the current (NM) 2 × I, the current sink P ₂ carries the current (NM) 2 × I and the current supplied to the positive input of the amplifier A _2. Is (n−k−
Equal to (N + M) / 2) I and the current supplied to the negative input of amplifier A ₂ is equal to-(nk- (N + M) / 2) I.

The following voltages appear at the positive and negative inputs of amplifier A ₂ , respectively.

[0045]

V− = V _cm −R (n−k− (N + M) / 2) I V + = V _cm + R (n−k− (N + M) / 2) I

The differential output voltage of this amplifier is as follows.

[0047]

## EQU00004 ## Vdiff = V + -V-.

The new digital-to-analog converter is produced by the mismatch in the digital-to-analog converter and in the current-to-voltage converter and filter without loss of dynamic range in terms of the digital code of the useful signal. It is possible to compensate for the offset voltage applied.

Finally, in order to minimize the gain error, the resistor used in the continuous low-pass filter is paired with the resistor that sets the reference current of the main digital-to-analog converter. To be done.

A possible embodiment is shown in FIG.

[0051] The circuit created based on the circuit of Figure 4 is connected to a current sink P _1, P _2, includes a differential-differential amplifier A _2, corresponding each to each input of the amplifier output Capacitors C ₁ and C ₂ are connected between and. The output of the differential / differential amplifier A ₂ is linked to the input of the additional differential / differential amplifier A ₄ via resistors R ₃ and R ₄ , respectively.

The negative output of the amplifier A ₄ is connected to the positive input of this amplifier by means of a circuit formed by a resistor R ₅ and a capacitor C ₅ connected in parallel.

Whereas the positive output of amplifier A ₄ is connected to the terminals of capacitor C ₆ and resistor R ₆ ,
The other terminals of the resistor R ₆ and the capacitor C ₆ connected in parallel are connected to the negative input of the amplifier A ₄ , and the connection between the resistor R ₆ and the capacitor C ₆ on the side opposite to this negative input is the connection of this circuit. Form the second output.

Furthermore, the positive input of amplifier A ₂ is connected by resistor R _{7 to} the negative output of amplifier A ₄ , whereas the negative input of amplifier A ₂ is resistor R ₆ and capacitor C _6.
A resistor R ₈ is connected to the output of this circuit formed by the connection with
Connected through.

The output of the circuit thus constructed is connected to the input of a comparator C _P , the output of which is linked to an offset compensation loop BCD.

The output of the loop BCD is the auxiliary switch I ₃₁
~I _3N, controls the I ₄₁ ~I _4N.

Current (n−k− (N + M) / 2) I and −
(N−k− (N + M) / 2) I is fed to the input of amplifier A ₂ .

Current (n−k− (N + M) / 2) I and −
(N−k− (N + M) / 2) I flow into resistors R ₇ and R ₈ , respectively, which are of the same value.

The following voltage appears at the negative output of the auxiliary amplifier A ₄ .

[0060]

V− = V _cm −R (n−k− (N + M) / 2) I

The following voltage appears at the output formed by the connection of resistor R ₆ and capacitor C ₆ .

[0062]

[Equation 6] V + = V _cm −R (n−k− (N + M) / 2) I

Therefore, the following differential output voltage appears at the output of this circuit.

[0064]

## EQU00007 ## Vdiff = V + -V-

[0065]

The addition of the comparator and control circuit allows the auxiliary digital-to-analog converter to be used for self-calibration of the offset voltage of the system including the main digital-to-analog converter and the filter.

With respect to the above description, the following items will be further disclosed.

(1) Digital / analog converter
The current source (S₁To S_N), Each of which
The source is the first current sink (P₁) Or a second current sink (P
_Two) Switch (I₁₁, I_{twenty one}, ... I_1N,
I_2N) With the current source associated with
The current source (S₁~
S _N) And the current sink derived by
(P₁, P_Two) Before the difference between the current absorbed by
Differential / differential conversion to a differential voltage related to the digital signal
Dynamic amplifier (A_Two) And each of the current sources
The first current sink for absorbing a constant value of the emitted current;
The second current sink (P₁, P_Two) And including the differential
・ Differential amplifier (A_Two) Form an active time filter,
The output voltage of the filter is generated by the converter.
Digital / analog characterized by forming an analog signal
Analog converter.

(2) Digital / analog according to item 1
Mode converter with two differential inputs
Amplifier (A_Three) Each of said inputs is said switch
(I₁₁, I _1N, ... I_{twenty one}, I_2N) First terminal and second terminal
Common mode voltage (V_cm) Is connected between
And the output of the mode control amplifier is the current sink (P
₁, P_Two) Mode control control for controlling the bias signal of
Digital / analog characterized by further including a width device
converter.

(3) Digital / analog according to item 2
Converter, while the switch (I₁₁,
I_1N, ... I_{twenty one}, I_2N) Connection point, and other
Control by digital offset code (k)
Additional switch (I₃₁To I _3N, I₄₁To I_4N)
Additional current sink (P₁₁, P_1M)
, The additional current sink and the associated switch of the additional current sink.
Is an auxiliary digital / analog for offset voltage compensation
Digital / analog characterized by forming a converter
Converter.

(4) In the digital / analog converter according to the third aspect, means for comparing the output signals of the differential / differential amplifier (A ₂ ) and the addition of the auxiliary digital / analog converter. Switches (I ₃₁ , I _3N , ... I ₄₁ , I
_4N ) control signal for offset compensation means (BC
D) includes a digital / analog converter.

(5) The digital / analog converter according to one of the third and fourth terms, wherein
Additional differential connected to the output of the differential amplifier (A ₂ ) The negative output of the differential amplifier (A ₄ ) is connected in parallel through a resistor (R ₅ ) and a capacitor (C ₅ )
Connected to the positive input of the differential amplifier (A ₄ ), the positive output of the additional differential / differential amplifier is one terminal of another capacitor (C ₆ ) and one terminal of another resistor (R ₆ ). And another terminal of the other resistor (R ₆ ) to which the negative inputs of the additional differential / differential amplifier (A ₄ ) are connected in parallel and the other capacitor (C ₆ ) respectively. Connected to the terminal of
The additional differential, the differential amplifier (A ₄₎ of a negative output, the additional differential, the differential amplifier (A ₄₎ at the negative input the other resistor (R ₆₎ with the other capacitors in the opposite end of (C ₆ )
Further comprising said additional differential-to-differential amplifier (A ₄ ) whose connection to forms the output of said digital-to-analog converter, and, on the other hand, two further resistors (R ₇ , R ₈ ).
Are respectively connected between the positive and negative outputs of the differential / differential amplifier (A ₂ ) and the negative and positive outputs of the additional differential / differential amplifier (A ₄ ), respectively. A digital / analog converter characterized in that

(6) A digital-to-analog converter, which is a current source (S ₁ to S _N ), each of which connects the current source to a first current sink (P ₁ ) or a second current sink (P ₁ ).
₂ ) switches for connection (I ₁₁ , I ₂₁ , ... I _1N ,
I _2N ) and the current sources (S ₁ to S) activated by the digital signal to be converted.
_N ) and the current sink (P ₁ ,
A differential-differential amplifier (A ₂ ) for converting the difference between the current absorbed by P ₂ ) into a differential voltage related to said digital signal, and a constant value of the current derived by each said current source Absorbing the first current sink and the second current sink
A current sink (P ₁ , P ₂ ), said differential-to-differential amplifier (A ₂ ) forming an active time filter, the output voltage of which forms the analog signal generated by said converter. A digital / analog converter characterized by:

[Brief description of drawings]

FIG. 1 is an electrical schematic of a prior art digital-to-analog converter with a single current sink.

FIG. 2 is an electric circuit diagram of a differential digital / analog converter according to an embodiment of the present invention.

FIG. 3 is an electric circuit diagram of a modified embodiment of the digital / analog converter of FIG. 2 according to the present invention.

4 is an electrical circuit diagram of another variant embodiment of the digital / analog converter of FIG. 2 according to the invention, showing the possibility of self-calibration of the offset voltage.

FIG. 5 is an electrical schematic diagram of an embodiment digital-to-analog converter and associated filter that can be used for self-calibration of the offset voltage of the system.

[Explanation of symbols]

A ₂ Differential Differential amplifier A ₃ mode control amplifier A ₄ additional differential-differential amplifier BCD offset compensation loop C _P comparator I ₁₁ ~I _1N switch I ₄₁ ~I _4N auxiliary switch I ₃₁ ~I _3N auxiliary switch P ₁ , P ₂ current sink P ₁ ~ P _1M current sink S ₁ ~ _SN current source

Claims (1)

[Claims] 1. A digital-to-analog converter comprising: current sources (S ₁ to S _N ) each of which comprises a first current sink (P ₁ ) or a second current sink (P _2). ) Switch (I ₁₁ , I ₂₁ , ... I _1N , I _2N )
Is absorbed by the current source is activated Te than a digital signal (S ₁ ~S _N) current and the current sink which is derived by (P _1, P ₂₎ of said current source, attempts to convert associated with A differential / differential amplifier (A ₂ ) for converting the difference between the current and the current into a differential voltage related to the digital signal, and the first differential amplifier for absorbing a constant value of the current derived by each of the current sources. A current sink and a second current sink (P ₁ , P ₂ ), wherein the differential / differential amplifier (A ₂ ) forms an active time filter, the output voltage of which is generated by the converter. A digital-to-analog converter characterized by forming an analog signal according to the above.