Directional sampling bridge

A directional sampling bridge for coupling a periodic incident wave to a device under test and for generating a first IF output signal indicative of the voltage of said incident wave and a second IF output signal indicative of any reflected wave from the device under test, comprising:

• a sampling signal input port for receiving said periodic incident wave;
• a strobe pulse input port for receiving local oscillators strobe pulses at a frequency which is near but less than the frequency of said periodic incident wave;
• means coupled to said strobe pulse input port and to said sampled signal input port for charging first and second circuit nodes to a voltage at the time of occurrence of each strobe pulse which is proportional to respectively, half the peak voltage of said strobe pulses plus the voltage of said periodic incident wave at the time of occurrence of said strobe pulses, and the voltage of said periodic incident wave at the time of occurrence of said strobe pulse minus half the peak voltage of said strobe pulses, and for summing the voltages at said first and second nodes to generate said first IF output signal;
• means coupled to said strobe pulse input port, said device under test and said sampled signal input port for charging third and fourth circuit nodes to voltages which are proportional to, respectively, ##EQU1## where V.sub.sp =the peak amplitude of each strobe pulse;
• V1-V2=the voltage between two nodes of a resistive directional bridge, neither of said nodes being connected to ground potential, which is proportional to or related to the amplitude of any periodic reflected wave from the device under test as exists at each of the times of occurrence of the strobe pulses.

A floating sampling apparatus for sampling a repetitive signal using the voltage difference between first and second nodes in a circuit, neitehr of which is grounded and for generating an output signal proportional thereto at a lower frequency than the frequency of said repetitive signal, comprising:

• a local oscillator input port for receiving local oscillator strobe pulses having a frequency near but lss than the frequency of said repetitive signal being sampled;
• a resistive directional bridge comprised of first, second and third resistors and a fourth impedance equal to the input impedance of a device under test, said input impedance and said resistors arranged into a Wheatstone bridge defining said first and second nodes, neither of which is connected to ground and third and fourth nodes defining an input port for receiving said repetivive signal being sampled, said third node eefined by the junction between said first and second resistors, said fourth node defined by the junction of said third resistor and said input impedance and connected to ground potential and coupled to said local oscillator input port through a local oscillator termination impedance, said first node being defined by the junction of said first resistor and said input impedance, and second second node defined by the junction of said third and second resistors;
• charge storage means coupled to said second node and coupled to be influenced by said strobe pulses through said third resistor, and having first and second output nodes, for storing charge so as to raise the voltage of said first and second output nodes, respectively, to two different voltage levels which are related to the peak voltage level of each strobe pulse and the instantaneous voltage level of said repetitive signal being sampled at the time of occurrence of said said strobe pulse, said different voltage levesl, when summed, give a voltage which is proportional to the voltage difference between said first and second nodes of said Wheatstone bridge at the time of occurrence of each said strobe pulse;
• and
• diode mans selectively coupling said first and second output nodes of said charge storage means to said first node of said Wheatstone bridge, for gating current selectively into said charge storage means during said strobe pulses, the amplitude of said current being related to the instantaneous amplitude of said repetitive signal being sampled at the time of occurrence of each said strobe pulse so as to cause predetermined charge buildup at said first and second output nodes of said charge storage means so as to cause said two different voltages at said first and second output nodes of said charge storage means.

A method of measuring a voltage difference between two nodes in a circuit neither of which is ground by equivalent time sampling without the use of a balun, comprising:

• applying a repetitive signal to be sampled to a device under test through said circuit;
• applying local oscillator strobe pulses through first and second selective gating devices to first and second capacitors which are coupled to said circuit such that the voltage to which said capacitors charge is influenced by said repetitive signal to be sampled, and selectively gating the charging current into said capacitors in a manner so as to cause said first capacitor to charge to a voltage ##EQU2## and to cause said second capacitor to charge to a voltage ##EQU3## where V.sub.sp =the peak amplitude of each strobe pulse;
• V1-V2 =the voltage between said two nodes neither of which is ground as exists at each of the times of occurrence of the strobe pulses;
• and
• summing the voltages to which said first and second capacitors have charged to generate an output signal proportional to V1-V2.