Ann: Archer and EPFL develop a single chip pulsed ESR microsystem, page-104

note 3 of the paper (ROOM TEMPRATURE)

3. Experimental set-up and results All experiments are performed at room temperature, in air, and in an ordinary laboratory without RF/MW shielding. The chip is glued on top of an FR4 printed circuit board (PCB) as shown in Fig. 1(a) using conductive epoxy (Epo-Tek, H20E-FC). The electrical connections from the chip to the PCB are made by wedge-wedge Au bonding wires having a diameter of 20 µm. The PCB is placed in a 0 to 2 T resistive electromagnet. The connections from the PCB to the external electronics are realized with four coaxial cables for the RF/MW connections (LOP, LON, EXC, VOUT P ) and three single pole wires for the DC connections (VDDRX, GND, VLO). As shown in Fig. 2, two microwave signal generators are used for the excitation and LO signals. The LO signal is splitted into two signals (LOP and LON), one of them is π phase shifted before reaching the chip. LOP and LON signals are separately biased using two 1 kΩ resistors soldered on PCB as shown in Fig. 1(a). On the excitation path, three switches (H) are implemented to shape the sinusoidal continues wave output of the signal generator (N). These switches are controlled by a multichannel programmable pulse generator (G) which produces LVTTL (0-3.3 V) pulses having a minimum length of 6 ns. The use of three switches in series allows to obtain an isolation about 100 dB. A power switch (S) is used after the amplifier to further increase the isolation and to reduce amplifier noise delivered to the excitation coil during the detection time of the ESR signal. In the IF signal path, the switch (Q) prevents the saturation of the external IF amplifier (R), avoiding a significant increase of the deadtime. The two microwave generators are frequency locked using the same 10 MHz reference signal. This assure a fixed frequency difference between the two generators (in our experiments 200 MHz). To allow for phase coherent time domain averaging of the ESR signals, the acquisition is triggered by the IF signal obtained by mixing the two generators using the mixer (P). This IF signal is shaped using the TTL output of a divider (T) and it passes through a switch (O) before reaching the trigger input of the data acquisition board (I). This allows to set the start of the data acquisition at the desired time with respect to the pulse sequence