Time-to-digital conversion device, ranging device, and movable body
A time-to-digital conversion device according to an embodiment of the present disclosure is a time-to-digital conversion device configured to output time digital data according to a time from a first timing to a second timing, including a first circuit that includes an upper counter configured to start counting a clock signal according to the first timing, and generates upper bits of the time digital data; a second circuit that includes a delay element configured to start operation according to the second timing and a lower counter configured to count an oscillation cycle of the delay element, and generates lower bits of the time digital data; and a control circuit that controls a phase of an output signal of the delay element based on the clock signal.
1 . A time-to-digital conversion device configured to output time digital data according to a time from a first timing to a second timing, comprising:
a first circuit that includes an upper counter configured to start counting a clock signal according to the first timing, and generates upper bits of the time digital data;
a second circuit that includes a delay element configured to start operation according to the second timing and a lower counter configured to count an oscillation cycle of the delay element, and generates lower bits of the time digital data; and
a control circuit that controls a phase of an output signal of the delay element based on the clock signal,
wherein the delay element is a voltage-controlled oscillator.
2 . The time-to-digital conversion device according to claim 1 , wherein the upper counter and the delay element stop operating after a predetermined period has elapsed from the second timing.
3 . The time-to-digital conversion device according to claim 2 , wherein the predetermined period is a timing synchronized with the clock signal.
4 . The time-to-digital conversion device according to claim 1 , wherein the delay element is a multiphase output voltage-controlled oscillator.
5 . The time-to-digital conversion device according to claim 4 , wherein the second circuit further comprises a lower encoder configured to encode a multiphase output of the delay element.
6 . The time-to-digital conversion device according to claim 5 , wherein the time digital data has a bit length (b1+b2+b3) and is represented by:
D coarse ×2 b 2 +b 3 −( D fine_cycle =2 b3 +D fine_phase ) (Expression 1),
where the upper bits are represented by data Dcoarse of bit length b1, data of the lower counter is represented by data Dfine_cycle of bit length b2, and data of the lower encoder is represented by data Dfine_phase of bit length b3.
7 . The time-to-digital conversion device according to claim 6 , further comprising a correction circuit configured to correct the time digital data,
wherein the correction circuit corrects the time digital data with data Dfine_cycle_tdclk of the lower counter and data Dfine_phase_tdclk of the lower encoder in a period of one cycle of the clock signal in accordance with the following expression:
D
coarse
×
2
b
2
+
b
3
-
2
b
2
+
b
3
(
D
fine
-
cycle
×
2
b
3
+
D
fine
_
phase
)
D
fine
-
cycle
-
tdclk
×
2
b
3
+
D
fine
_
phase
-
tdclk
=
2
b
2
+
b
3
(
D
coarse
-
(
D
fine
-
cycle
×
2
b
3
+
D
fine
_
phase
)
D
fine
-
cycle
-
tdclk
×
2
b
3
+
D
fine
_
phase
-
tdclk
)
.
(
Expression
2
)
8 . The time-to-digital conversion device according to claim 7 , wherein the correction circuit calculates the data Dfine_cycle_tdclk of the lower counter and the data Dfine_phase_tdclk of the lower encoder by dividing the data Dfine_cycle of the lower counter and the data Dfine_phase of the lower encoder in N cycles (N is a positive integer) of the clock signal by N.
9 . The time-to-digital conversion device according to claim 7 , further comprising a switching circuit configured to switch an operation mode of the second circuit,
wherein the switching circuit causes:
in a first operation mode, the delay element to be operated until a predetermined period of time has elapsed from the second timing; and
in a second operation mode, the delay element to be operated during N cycles (N is a positive integer) of the clock signal.
10 . The time-to-digital conversion device according to claim 1 , wherein the delay element is a voltage-controlled delay line.
11 . The time-to-digital conversion device according to claim 1 ,
wherein the time digital data has a bit length (b1+b2) and is represented by:
D coarse×2 b2 −D fine (Expression 3),
where the upper bits are represented by data Dcoarse of a bit length b1 and the lower bits are represented by data Dfine of a bit length b2.
12 . The time-to-digital conversion device according to claim 11 , further comprising a correction circuit configured to correct the time digital data,
wherein the correction circuit corrects the time digital data with the data Dfine_tdclk of the lower bits in a period of one cycle of the clock signal in accordance with the following expression:
D coarse×2 b2 −( D fine/ D fine_tdclk)×2 b2 (Expression 4).
13 . A time-to-digital conversion device, configured to output time digital data according to a time from a first timing to a second timing, comprising:
a first circuit that includes an upper counter configured to start counting a clock signal according to the first timing, and generates upper bits of the time digital data;
a second circuit that includes a delay element configured to start operation according to the second timing and a lower counter configured to count an oscillation cycle of the delay element, and generates lower bits of the time digital data;
a control circuit that controls a phase of an output signal of the delay element based on the clock signal,
wherein the control circuit includes:
a replica circuit of the delay element of the second circuit; and
a phase synchronization circuit that feeds back to the replica circuit a control voltage based on a comparison between a phase of a divided signal of an output signal of the replica circuit and a phase of the clock signal and,
wherein the control circuit further supplies the control voltage to the delay element of the second circuit.
14 . The time-to-digital conversion device according to claim 13 , further comprising a plurality of the first circuits and a plurality of the second circuits,
wherein the control circuit supplies the control voltage to the plurality of delay elements of the plurality of second circuits.
15 . A ranging device comprising:
a time-to-digital conversion device configured to output time digital data according to a time from a first timing to a second timing, the time-to-digital conversion device comprising:
a first circuit that includes an upper counter configured to start counting a clock signal according to the first timing, and generates upper bits of the time digital data;
a second circuit that includes a delay element configured to start operation according to the second timing and a lower counter configured to count an oscillation cycle of the delay element, and generates lower bits of the time digital data; and
a control circuit that controls a phase of an output signal of the delay element based on the clock signal; and
a light receiving unit that receives pulse light emitted toward an object and reflected by the object,
wherein the time-to-digital conversion device acquires distance information to the object based on the time digital data corresponding to a time from the first timing to the second timing using an emission timing of the pulse light as the first timing and a reception timing of the pulse light as the second timing.
16 . The ranging device according to claim 15 ,
wherein a plurality of the light receiving units are arranged in a plurality of rows and a plurality of columns,
wherein the first circuit and the second circuit are provided for each row, and
wherein the control circuit is shared by a plurality of the second circuits.
17 . The ranging device according to claim 15 ,
wherein a plurality of the light receiving units are arranged in a plurality of rows and a plurality of columns,
wherein the first circuit and the second circuit are provided for each of the light receiving units, and
wherein the control circuit is shared by a plurality of the second circuits.
18 . The ranging device according to claim 15 ,
wherein a plurality of the light receiving units are arranged in a plurality of rows and a plurality of columns,
wherein the first circuit and the second circuit are provided for each sub-array including the plurality of light receiving units, and
wherein the control circuit is shared by a plurality of the second circuits.
19 . A movable body comprising:
the ranging device according to claim 15 , and
a control unit configured to control the movable body based on the distance information acquired by the ranging device.