Test apparatus for digital modulated signal
View Patent ↗A test apparatus includes digital modulators provided in increments of multiple channels. A baseband signal generator performs retiming of data input as a modulation signal for the in-phase (quadrature) component, using a timing signal the timing of which can be adjusted, thereby generating a baseband signal. A driver generates a multi-value digital signal having a level that corresponds to the baseband signal output from the baseband signal generator. A multiplier amplitude-modulates a carrier signal with the multi-value digital signal. An adder sums the output signals of the multipliers.
1. A test apparatus configured to supply data subjected to digital multi-value modulation to a device under test configured to transmit and receive multiple channels of data subjected to digital multi-value modulation, wherein the test apparatus comprises digital modulators in increments of channels, and wherein the digital modulator comprises: a first baseband signal generator configured to perform retiming of first data input as a modulation signal for an in-phase component using a first timing signal the timing of which can be adjusted, so as to generate a first baseband signal;
a second baseband signal generator configured to perform retiming of second data input as a modulation signal for a quadrature component using a second timing signal the timing of which can be adjusted, so as to generate a second baseband signal;
a first multi-level driver configured to generate a first multi-value digital signal having a level that corresponds to the value of the baseband signal output from the first baseband signal generator;
a second multi-level driver configured to generate a second multi-value digital signal having a level that corresponds to the value of the baseband signal output from the second baseband signal generator;
a first multiplier configured to amplitude-modulate an in-phase carrier signal with the first multi-value digital signal;
a second multiplier configured to amplitude-modulate a quadrature carrier signal with the second multi-value digital signal; and
an adder configured to sum the output signals of the first and second multipliers.
2. A test apparatus according to claim 1 , wherein the first baseband signal generator comprises a first data rate setting unit configured to convert the bit rate of first data generated by a pattern generator into a bit rate that corresponds to the first timing signal, and wherein the second baseband signal generator comprises a second data rate setting unit configured to convert the bit rate of second data generated by the pattern generator into a bit rate that corresponds to the second timing signal.
3. A test apparatus according to claim 1 , wherein the first baseband signal generator comprises a first waveform format controller configured to set a waveform mode for the first baseband signal, and wherein the second baseband signal generator comprises a second waveform format controller configured to set a waveform mode for the second baseband signal.
4. A test apparatus according to claim 1 , wherein the first and second multi-level drivers are each configured such that the output level can be adjusted.
5. A test apparatus according to claim 4 , wherein the output level of the first multi-level driver and the output level of the second multi-level driver can be independently adjusted.
6. A test apparatus according to claim 3 , wherein the first and second multi-level drivers are each configured as an M-level (M=2N) driver configured to receive a baseband signal having an N-bit (N represents an integer) differential format, and wherein the first and second multi-level drivers each include N differential amplifiers, and wherein each differential amplifier comprises: a differential pair configured to receive the baseband signal such that the bits of the baseband signal are input in a differential format;
a tail current source configured to bias the differential pair; and
an output load circuit for the differential pair, and wherein the output load circuit is shared by the N differential amplifiers, and wherein tail currents generated by the tail current sources of the N differential amplifiers can be independently controlled.
7. A test apparatus according to claim 1 , wherein the first and second multipliers are each configured such that the gains thereof can be independently adjusted.
8. A test apparatus according to claim 1 , further comprising: an oscillator configured to generate a carrier signal having a carrier frequency; and
a phase shifter configured to shift the phase of the carrier signal generated by the oscillator so as to generate the in-phase carrier signal and the quadrature carrier signal.
9. A test apparatus according to claim 8 , wherein the phase shifter is configured such that the phase difference between the in-phase carrier signal and the quadrature carrier signal can be adjusted.
10. A test apparatus according to claim 1 , wherein the in-phase carrier signal and the quadrature carrier signal are each generated in the form of a rectangular pulse signal.
11. A test apparatus according to claim 1 , further comprising: a direct digital synthesizer configured to digitally generate a user-desired signal waveform; and
a digital/analog converter configured to perform digital/analog conversion of the output data output from the direct digital synthesizer, and to generate the in-phase carrier signal and the quadrature carrier signal.
12. A test apparatus according to claim 1 , further comprising a timing generator configured to generate a pulse signal having a frequency and a level transition timing which can be set as desired, wherein the in-phase carrier signal and the quadrature carrier signal are generated by means of the timing generator.