Differential amplifier, digital-to-analog converter and display device

• US 7,443,234 B2
• Filed: 03/21/2007
• Issued: 10/28/2008
• Est. Priority Date: 03/23/2006
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Iriguchi, Masao
• Primary Examiner(s): Nguyen; Khanh V
• Application Number:
  US11/689,340
• Publication Number:
  US 20070236289A1
• Time in Patent Office: 587 Days
• Field of Search: 330/9, 330/253, 330/257, 330/258, 330/260
• US Class Current: 330/9
• CPC Class Codes: H03F 2203/45212 the differential amplifier being designed to have a reduced offset
• CPC Class Codes: H03F 2203/45536 the FBC comprising a switch and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45588 the IC comprising offset compensating means
• CPC Class Codes: H03F 2203/45616 the IC comprising more than one switch, which are not cross coupled
• CPC Class Codes: H03F 2203/45681 the LC comprising offset compensating means
• CPC Class Codes: H03F 2203/45726 the LC comprising more than one switch, which are not cross coupled
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence
• CPC Class Codes: H03F 3/45744 by offset reduction
• CPC Class Codes: H03F 3/45748 by using a feedback circuit
• CPC Class Codes: H03M 1/0607 Offset or drift compensation removal of offset already present on the analogue input signal H03M1/1295

Abstract

Disclosed are a multi-level differential amplifier that includes first to third input terminals; an output terminal; first to third differential pairs; a current source circuit for supplying currents to the respective first to mth differential pairs; a load circuit connected to first and second nodes to which first and second outputs of each of output pairs of the first to third differential pairs are connected in common; an amplifier stage receiving a signal from at least one node of the first and second nodes as an input and having its output connected to the output terminal; and a capacitance element. A data output period includes first and second periods. In the first period, responsive to a control signal, a first input of each input pair of the first to third differential pairs is made a non-inverting input, the second input is made an inverting input, the first inputs are connected to the respective first to third input terminals, and the second inputs of the first to third differential pairs are connected in common with one end of the capacitance element and with the output terminal. In the second period, responsive to a control signal, the first input of each input pair of the first to third differential pairs is made an inverting input and the second input is made a non-inverting input, the first inputs of each of the input pairs are connected in common with the output terminal, and the second inputs are connected in common with the one end of the capacitance element.

Claims

1. A differential amplifier comprising:

first to mth (where m is an integer equal to or greater than

     2) input terminals;

an output terminal;

first to mth differential pairs;

a current source circuit that supplies currents to respective ones of said first to mth differential pairs;

a first node connected in common with first outputs of each of output pairs of said first to mth differential pairs;

a second node connected in common with second outputs of each of output pairs of said first to mth differential pairs;

a load circuit connected to said first and second nodes;

an amplifier stage that receives a signal from at least one node of said first and second nodes as an input and has an output end connected to said output terminal;

a capacitance element; and

a changeover circuit that controls changeover between a first connection state and a second connection state, responsive to a control signal supplied thereto;

wherein

in said first connection state,

a first input of each input pair of said first to mth differential pairs is made a non-inverting input and a second input of each input pair of said first to mth differential pairs is made an inverting input,

the first inputs of the input pairs of said first to mth differential pairs are connected to respective ones of said first to mth input terminals, and

the second inputs of the input pairs of said first to mth differential pairs are connected in common with one end of said capacitance element and in common with said output terminal; and

in said second connection state,

the first input of each input pair of said first to mth differential pairs is made an inverting input and a second input of each input pair of said first to mth differential pairs is made a non-inverting input,

the first inputs of the input pairs of said first to mth differential pairs are connected in common with said output terminal, and

the second inputs of the input pairs of said first to mth differential pairs are connected to the one end of said capacitance element;

a first period in which the first connection state is selected and a second period which follows the first period and in which the second connection state is selected forming a data output period.

2. The differential amplifier according to claim 1, wherein,

in the first period, responsive to the control signal,

first to mth input voltages (Vin1, Vin2, . . . , Vinm) are applied to the first inputs of the input pairs of said first to mth differential pairs, respectively, and

a voltage that is the result of adding a voltage obtained by weighting and averaging the first to mth input voltages at prescribed ratios (a1, a2, . . . , am) and an offset voltage ascribable to said first to mth differential pairs is applied to the one end of said capacitance element, as expressed by the following equation:

$\mathrm{Vout}=\frac{a<br><br><br><br>1·<br><br>\mathrm{Vin}<br><br><br><br>1+a<br><br><br><br>2·<br><br>\mathrm{Vin}<br><br><br><br>2+\mathrm{\dots <br><br>}+\mathrm{am}·<br><br>\mathrm{Vinm}}{a<br><br><br><br>1+a<br><br><br><br>2+\mathrm{\dots <br><br>}+\mathrm{am}<br><br>}+\mathrm{Vof},$

 

where Vin1, Vin2, , and Vinm are input voltages,

a1, a2, . . . , and am are weightings of the respective input voltages, and

Vof is the offset voltage; and

in the second period, responsive to the control signal,

a voltage that has been stored in said capacitance element is applied to the second inputs of the input pairs of said first to mth differential pairs,

the offset voltage is corrected, and

a voltage obtained by weighting and averaging the first to mth input voltages (Vin1, Vin2, . . . , Vinm) at the prescribed ratio, as expressed by the following equation;

$\mathrm{Vout}=\frac{a<br><br><br><br>1·<br><br>\mathrm{Vin}<br><br><br><br>1+a<br><br><br><br>2·<br><br>\mathrm{Vin}<br><br><br><br>2+\mathrm{\dots <br><br>}+\mathrm{am}·<br><br>\mathrm{Vinm}}{a<br><br><br><br>1+a<br><br><br><br>2+\mathrm{\dots <br><br>}+\mathrm{am}}$

 

is output.

3. The differential amplifier according to claim 1, wherein

said current source circuit comprises first to mth current sources for supplying currents to respective ones of said first to mth differential pairs.

4. The differential amplifier according to claim 3, wherein

a ratio of channel widths of transistors constructing said first to mth differential pairs is made a1²:

a2²;

am²; and

a ratio of current values of said first to mth current sources is made 1;

1;

. . . ;

1.

5. The differential amplifier according to claim 1, wherein said current source circuit comprises a single current source for supplying current to all of said first to mth differential pairs.

6. The differential amplifier according to claim 5, wherein

a ratio of channel widths of transistors constructing said first to mth differential pairs is made a1²:

a2²;

. . . ;

am².

7. The differential amplifier according to claim 1, wherein

said changeover circuit includes:

first to mth input switches that perform on-and-off control of connections between the first inputs of the input pairs of said first to mth differential pairs and said first to mth input terminals, respectively;

first to mth negative-feedback connection switches that perform on-and-off control of connections between said output terminal and the respective first inputs of the input pairs of said first to mth differential pairs; and

a first switch that performs on-and-off control of a connection between one end of said capacitance element and said output terminal.

8. The differential amplifier according to claim 7, wherein

in the first period, responsive to the control signal,

said first to mth input switches are set in an ON state,

said first to mth negative-feedback connection switches are set in an OFF state,

said first switch is set in an ON state, and

said output terminal is connected to one end of said capacitance element via said first switch;

and

in the second period, responsive to the control signal,

said first to mth input switches are set in an OFF state,

said first to mth negative-feedback connection switches are set in an ON state,

said first switch is set in an OFF state, the second inputs of the input pairs of said first to mth differential pairs are connected in common with one end of said capacitance element, and

said output terminal is connected to the first inputs of the input pairs of said first to mth differential pairs via said first to mth negative-feedback connection switches.

9. The differential amplifier according to claim 1, wherein

said changeover circuit includes:

a fourth switch for performing on-and-off control of a connection between said first node and the input end of said amplifier stage, and

a fifth switch for performing on-and-off control of a connection between said second node and the input end of said amplifier stage.

10. The differential amplifier according to claim 9, wherein

in the first period, responsive to the control signal, said fifth switch is turned off and said first node is connected to the input end of said amplifier stage via said fourth switch, which is in an ON state;

and

in the second period, responsive to the control signal, said fourth switch is turned off and said second node is connected to the input end of said amplifier stage via said fifth switch, which is in an ON state.

11. The differential amplifier according to claim 1, wherein

said amplifier stage includes:

a differential amplifier stage;

a sixth switch that performs on-and-off control of a connection between said first node and a first input of an input pair of said differential amplifier stage;

a seventh switch that performs on-and-off control of a connection between said first node and a second input of the input pair of said differential amplifier stage;

an eighth switch that performs on-and-off control of a connection between said second node and the second input of the input pair of said differential amplifier stage; and

a ninth switch that performs on-and-off control of a connection between said second node and the first input of the input pair of said differential amplifier stage.

12. The differential amplifier according to claim 11, wherein

in the first period, responsive to the control signal,

said seventh and ninth input switches are set in an OFF state,

said first node is connected to the first input of the input pair of said differential amplifier stage via said sixth switch, which is in an ON state, and

said second node is connected to the second input of the input pair of said differential amplifier stage via said eighth switch, which is in an ON state;

and

in the second period, responsive to the control signal,

said sixth and eighth input switches are set in an OFF state,

said second node is connected to the first input of the input pair of said differential amplifier stage via said ninth switch, which is in an ON state, and

said first node is connected to the second input of the input pair of said differential amplifier stage via said seventh switch, which is in an ON state.

13. The differential amplifier according to claim 1, wherein

said load circuit includes a current mirror circuit, and wherein

changeover is controlled by the control signal in such a manner that in the first period, said first node is connected to an output of the current mirror circuit and said second node is connected to an input of the current mirror circuit, and

in the second period, said first node is connected to the input of the current mirror circuit and the second node is connected to the output of the current mirror circuit.

14. The differential amplifier according to claim 1, wherein

said load circuit includes:

first and second transistors that constitute a current mirror circuit and have sources connected in common to a power source and gate coupled together;

a third switch that performs on-and-off control of a connection between the gate and drain of said first transistor; and

a second switch that performs on-and-off control of a connection between the gate and drain of said second transistor;

the drains of said first and second transistors being connected to said first and second nodes, respectively;

wherein

in the first period, responsive to the control signal,

said third switch is set in an OFF state and said second switch is set in an ON state, whereby said second transistor is diode-connected and said second and first nodes are made the input and output, respectively, of the current mirror circuit; and

in the second period, responsive to the control signal,

said second switch is set in an OFF state and said third switch is set in an ON state, whereby said first transistor is diode-connected and said first and second nodes are made the input and output, respectively, of the current mirror circuit.

15. The differential amplifier according to claim 1, further comprising an output switch that performs on-and-off control of a connection between said output terminal and an external load;

said output switch being turned by the control signal in the first period.

16. The differential amplifier according to claim 7, wherein

said first switch that performs on-and-off control of the connection between one end of said capacitance element and said output terminal has a third transistor;

said differential amplifier includes a fourth transistor that has source and drain short-circuited between the drain or source of said third transistor and one end of said capacitance element;

a first control signal is supplied to the gate of said third transistor;

a second control signal is supplied to the gate of said fourth transistor; and

the second control signal is a signal that is the inverse of the first control signal.

17. A digital-to-analog converter comprising:

a differential amplifier set forth in claim 1;

a resistor string including a plurality of resistance elements connected serially between a first potential on a high-potential side and a second potential on a low-potential side; and

a selecting circuit which receives potentials from taps of said resistor string and selects input voltages, which are to be supplied to a plurality of the input terminals, based upon a selection signal.

18. A display device having an amplifying circuit that drives a data line connected to a display element, wherein said display device has the differential amplifier set forth in claim 1 as said amplifying circuit.

19. A display device including:

a first data line and a second data line adjacent to said first data line;

a first differential amplifier for charging and a second differential amplifier for discharging, each of said first and second differential amplifier being the differential amplifier as set forth in claim 1;

first and second output switches arranged between an output of said first differential amplifier and said first and second data lines, respectively;

third and fourth output switches arranged between an output of said second differential amplifier and said first and second data lines, respectively;

wherein said second and third output switches are set in an OFF state and said first and fourth output switches are set in an ON state in a prescribed data output period; and

said first and fourth output switches are set in an OFF state and said second and third output switches are set in an ON state in a data output period that follows the prescribed data output period.

20. A display device including:

a first data line and a second data line adjacent to said first data line;

a first differential amplifier for charging and a second differential amplifier for discharging, each of said first and second differential amplifier being the differential amplifier as set forth in claim 1;

first and second output switches arranged between an output of said first differential amplifier and said first and second data lines, respectively;

third and fourth output switches arranged between an output of said second differential amplifier and said first and second data lines, respectively;

wherein

control is exercised in such a manner that in a prescribed data output period, said second and third output switches are set in an OFF state and said first and fourth output switches are set in an ON state after being placed in an OFF state for a prescribed period of time from start of the data output period; and

control is exercised in such a manner that in a data output period that follows the prescribed data output period, said first and fourth output switches are set in an OFF state and said second and third output switches are set in an ON state after being placed in an OFF state for a prescribed period of time from start of the data output period.

21. A differential amplifier comprising:

first and second input terminals;

an output terminal;

first and second differential pairs;

a current source circuit that supplies currents to respective ones of said first and second differential pairs;

a first node connected in common with first outputs of each of output pairs of said first and second differential pairs;

a second node connected in common with second outputs of each of output pairs of said first and second differential pairs;

a load circuit connected to said first and second nodes;

an amplifier stage that receives a signal from at least one node of said first and second nodes as an input and has an output end connected to said output terminal;

a capacitance element; and

a changeover circuit that controls changeover between a first connection state and a second connection state, responsive to a control signal input thereto, wherein

in said first connection state,

a first input of each input pair of said first and second differential pairs is made a non-inverting input and a second input of each input pair of said first and second differential pairs is made an inverting input,

the first input of the input pair of said first differential pair is connected to said first input terminal,

the first input of the input pair of said second differential pair is connected to said second input terminal, and

the second inputs of the input pairs of said first and second differential pairs are connected in common with one end of said capacitance element and in common with said output terminal; and

in said second connection state,

the first input of each input pair of said first and second differential pairs is made an inverting input and a second input of each input pair of said first and second differential pairs is made a non-inverting input,

the first inputs of the input pairs of said first and second differential pairs are connected in common with said output terminal, and

the second inputs of the input pairs of said first and second differential pairs are connected to the one end of said capacitance element;

a first period in which the first connection state is selected and a second period which follows the first period and in which the second connection state is selected forming a data output period.

22. The differential amplifier according to claim 21, wherein

changeover is controlled by the control signal in such a manner that

in the first period,

first and second input voltages (Vin1, Vin2) are applied to the first inputs of the input pairs of said first and second differential pairs, respectively, and

a voltage that is the result of adding a voltage obtained by internally dividing the first and second input voltages at a ratio (a2:

a1) and an offset voltage ascribable to said first and second differential pairs is stored at one end of said capacitance element, as expressed by the following equation;

$\mathrm{Vout}=\frac{a<br><br><br><br>1·<br><br>\mathrm{Vin}<br><br><br><br>1+a<br><br><br><br>2·<br><br>\mathrm{Vin}<br><br><br><br>2}{a<br><br><br><br>1+a<br><br><br><br>2}+\mathrm{Vof},$

 

where Vin1 and Vin2 are input voltages,

a1 and a2 are weightings of the respective input voltages, and

Vof is the offset voltage; and

in the second period,

a voltage that has been stored in said capacitance element is input in common to all of the second inputs of the input pairs of said first and second differential pairs,

the offset voltage is corrected, and

a voltage obtained by internally dividing the two input voltages at the prescribed ratio (a2;

a1), as expressed by the following equation;

$\mathrm{Vout}=\frac{a<br><br><br><br>1·<br><br>\mathrm{Vin}<br><br><br><br>1+a<br><br><br><br>2·<br><br>\mathrm{Vin}<br><br><br><br>2}{a<br><br><br><br>1+a<br><br><br><br>2}$

 

is output.

23. The differential amplifier according to claim 21, wherein

said current source circuit comprises a first current source for supplying current to said first differential pair and a second current source for supplying current to said first second differential pair.

24. The differential amplifier according to claim 23, wherein

a ratio of channel width of transistors constructing said first differential pair and channel width of transistors constructing said second differential pair is made a1²:

a2²; and

a ratio of current values of said first and second current sources is made 1;

1.

25. The differential amplifier according to claim 21, wherein

said changeover circuit includes:

a first input switch that performs on-and-off control of a connection between the first input of the input pair of said first differential pair and said first terminal;

a second input switch that performs on-and-off control of a connection between the first input of the input pair of said second differential pair and said second terminal;

a first negative-feedback connection switch that performs on-and-off control of a connection between said output terminal and the first input of the input pair of said first differential pair;

a second negative-feedback connection switch that performs on-and-off control of a connection between said output terminal and the first input of the input pair of said second differential pair; and

a first switch that performs on-and-off control of a connection between one end of said capacitance element and said output terminal.

26. The differential amplifier according to claim 25, wherein

in the first period, responsive to the control signal,

said first and second input switches are set in an ON state,

said first and second negative-feedback connection switches are set in an OFF state,

said first switch is set in an ON state, and

said output terminal is connected to the one end of said capacitance element via said first switch;

and

in the second period, responsive to the control signal,

said first and second input switches are set in an OFF state,

said first and second negative-feedback connection switches are set in an ON state,

said first switch is set in an OFF state,

the second inputs of the input pairs of said first and second differential pairs are connected in common with the one end of said capacitance element, and

said output terminal is connected to the first inputs of the input pairs of said first and second differential pairs via said first and second negative-feedback connection switches.

27. The differential amplifier according to claim 22, wherein the internal dividing ratio is made 1:

2 or 2;

1; and

a voltage value obtained by adding a voltage that is twice one of the first and second input voltages and the other voltage of the first and second voltages is made three times the output voltage in the second period.

28. The differential amplifier according to claim 27, wherein a ratio of channel width of transistors constructing said first differential pair and channel width of transistors constructing said second differential pair is made 4:

1 or 1;

4, and a ratio of current values of the two current sources is made 1;

1.

29. A differential amplifier comprising:

first and second input terminals;

an output terminal;

first to third differential pairs;

first to third current source circuits that supply currents individually to respective ones of said first to third differential pairs;

a first node forming a common connection node of first outputs of each of output pairs of said first to third differential pairs;

a second node forming a common connection node of second outputs of each of output pairs of said first and second differential pairs;

a load circuit connected to said first and second nodes;

an amplifier stage that receives a signal from at least one node of said first and second nodes as an input and has an output end connected to said output terminal;

a single capacitance element; and

a changeover circuit that controls changeover between a first connection state and a second connection state, responsive to a control signal supplied thereto;

wherein

first and second input voltages of mutually different voltage values are applied to said first and second input terminals, respectively;

element sizes of said first to third differential pairs are all made identical;

current quantities of said first to third current sources are all made identical; and

first inputs of input pairs of said first and second differential pairs are connected together and second inputs of input pairs of said first and second differential pairs are connected together; and

wherein

in said first connection state,

a first input of each input pair of said first to third differential pairs is made a non-inverting input and a second input of each input pair of said first to third differential pairs is made an inverting input,

the first input voltage is applied to the first inputs of said first and second differential pairs,

the second input voltage is applied to the first input of said first third differential pair, and

the second inputs of the input pairs of said first to third differential pairs are connected in common with one end of said capacitance element and in common with said output terminal; and

in the second connection state,

a first input of each input pair of said first to third differential pairs is made an inverting input and a second input of each input pair of said first to third differential pairs is made a non-inverting input,

the first inputs of the input pairs of said first to third differential pairs are connected in common with said output terminal,

the second inputs of the input pairs of said first to third differential pairs are connected in common with one end of said capacitance element, and

a voltage obtained by internally dividing the first and second input voltages at 1;

2 is amplified and output;

a first period in which the first connection state is selected and a second period which follows the first period and in which the second connection state is selected forming a data output period.