Driving circuit for optical device
A driving circuit includes a plurality of differential amplifier circuits each electrically connected to a power supply line. Each differential amplifier circuit includes a differential pair circuit and a series resistance circuit. In the differential pair circuit, a first transistor and a second transistor are electrically connected to the power supply line through a first load resistor and a second load resistor, respectively. A center node is electrically connected between the first transistor and the second transistor. Each differential amplifier circuit generates a differential output signal in accordance with a differential incoming signal. The series resistance circuit includes a resistor and a line element. The line element includes a signal line which extends straight with a distance between the signal line and a ground line extending in parallel thereto. The resistor and the line element are connected in series between the center node and a static potential line.
1. A driving circuit comprising:
a plurality of differential amplifier circuits each electrically connected to a power supply line, and each differential amplifier circuit including a differential pair circuit and a series resistance circuit,
wherein the differential pair circuit includes:
a first load resistor,
a second load resistor,
a first transistor having a control terminal, a first current terminal, and a second current terminal, the first current terminal being electrically connected to the power supply line through the first load resistor,
a second transistor having a control terminal, a first current terminal, and a second current terminal, the first current terminal of the second transistor being electrically connected to the power supply line through the second load resistor, and
a center node electrically connected between the second current terminal of the first transistor and the second current terminal of the second transistor,
wherein the control terminal of the first transistor and the control terminal of the second transistor receive a differential incoming signal, and the first load resistor and the second load resistor generate a differential output signal in accordance with the differential incoming signal,
wherein the series resistance circuit includes:
a resistor, and
a line element including a signal line having a width, the signal line extending straight in one direction with a distance between the signal line and a ground line extending in parallel to the signal line,
wherein the resistor and the line element are connected in series between the center node of the differential pair circuit and a static potential line.
2. The driving circuit according to claim 1 ,
wherein the differential incoming signal has a fundamental frequency, and the series resistance circuit has an impedance viewed from the center node, and
wherein the impedance at a frequency twice the fundamental frequency is larger than a resistance of the resistor.
3. The driving circuit according to claim 2 , wherein the impedance at the frequency twice the fundamental frequency is larger than 10 times the resistance of the resistor.
4. The driving circuit according to claim 2 , wherein the impedance at the frequency twice the fundamental frequency is larger than 20 times the resistance of the resistor.
5. The driving circuit according to claim 2 , wherein the fundamental frequency is 15 GHz or more and 60 GHz or less.
6. The driving circuit according to claim 2 , wherein the impedance viewed from the center node at a frequency twice the fundamental frequency is 100Ω or more.
7. The driving circuit according to claim 1 ,
wherein the differential incoming signal has a fundamental frequency, and the series resistance circuit has an impedance viewed from the center node, and
wherein the impedance at a frequency twice the fundamental frequency is larger than the impedance at the fundamental frequency.
8. The driving circuit according to claim 7 , wherein the fundamental frequency is 15 GHz or more and 60 GHz or less.
9. The driving circuit according to claim 7 , wherein the impedance viewed from the center node at a frequency twice the fundamental frequency is 100Ω or more.
10. The driving circuit according to claim 1 , wherein the line element is electrically connected between the center node and the resistor of the series resistance circuit.
11. The driving circuit according to claim 1 , wherein the line element has a coplanar transmission line structure.
12. The driving circuit according to claim 1 , wherein the line element has a microstrip line structure.
13. The driving circuit according to claim 1 ,
wherein the differential pair circuit further includes:
a third transistor having a control terminal, a first current terminal, and a second current terminal, the first current terminal being electrically connected to the power supply line through the first load resistor, the second current terminal being electrically connected to the first current terminal of the first transistor, and
a fourth transistor having a control terminal, a first current terminal, and a second current terminal, the first current terminal being electrically connected to the power supply line through the second load resistor, the second current terminal being electrically connected to the first current terminal of the second transistor,
wherein the control terminals of the third and fourth transistors are configured to receive a bias voltage.
14. The driving circuit according to claim 1 , wherein each of the differential amplifier circuits includes a pre-buffer at a front stage of the differential pair circuit.