Double balanced mixer

The amplified signal is passed to a double-balanced mixer configured as a phase-sensitive detector where the two inputs are the NMR signal (cOq) and the frequency of the synthesizer (03. gf) with the output proportional to cos(coq - co gj.)t + 0) + cos((coq + + 9). The sum frequency is much larger than the total bandwidth of the... 

Fig. 1. Set-up of the PTB laser system. The Nd YAG laser is frequency stabilized onto a selected iodine absorption line using the phase modulation method. The probe beam is modulated at 2.05 MHz by an electro-optic modulator (EOM), the pumb beam is frequency shifted by an acousto-optical modulator (AOM). The driving AOM rf power is chopped in order to cancel frequency offsets introduced by the Doppler background using a lock-in detection scheme. The transmitted probe beam signal is detected by a photodiode (PD) and mixed with the EOM rf in a double balanced mixer (DBM)...

Fig. 13. The preamplifier unit. The delayed incoming pulse (input 2 of the triple OR gate) assures a glitch-free protection pulse for the switch (a double-balanced mixer). A typical setting of the monoflop is 0.3 /us.

Fig. 14. Leak-compensated double-balanced mixer. Isolation > 70 dB.

Fig. 15. The pulse shaper. The gate is a DMF2A 5-1000 double-balanced mixer from Merrimac. R = 300 fl, R = 18 fl, and C = 270 pF. The bottom part shows how a properly delayed, shortened dc pulse is generated. The signal at TTL in is any of the +x, x, -t-y, or -y mixer-driver pulses generated in the phase shifter/mixer unit. TTL out is used to drive the switch in the preamplifier unit into its off state.

The initially amplified signal is then usually detected in the receiver using a three-port device acting as a double-balanced mixer. Three port devices, which can be used as gates, mixers or phase-sensitive detectors, consist of a series of diodes and transformer coils. The phase-sensitive detector has two input signals, the NMR signal (wq) and the frequency of the synthesiser (Wref)- The output is proportional to... 

Typical on-off ratios quoted in the literature for transmitters are in the neighborhood of 80-120 dB (a voltage attenuation factor of four to six orders of magnitude see VI.E.3.) which is large enough that it is not easy to measure. This on-off ratio is usually achieved with a combination of a standard switch (built, for example, out of commercial double balanced mixers) with 70-80 dB attenuation and additional gating of the amplifier(s). 

Each of the mixers (called phase sensitive detectors, mixers, or double balanced mixers abbreviated as DBM in the figure) will form the sum and difference of the input frequencies. The IF amplifier is tuned to Vj and all other frequencies will be discriminated against. The result is that the signal... 

The frequency synthesizer is a General Radio (now Gen-Rad) model GR 1164-A with the range 0.01-70 MHz. It is used to provide the frequencies referred to as v+10 MHz and 5 MHz. The 5 MHz is then doubled by a doubler (Relcom D8E) to provide the 10 MHz intermediate frequency. The double balanced mixers are Vari-L model DB-100B. 

A double balanced mixer is a three port device. When two frequencies are presented at two of the ports, the sum and difference frequencies appear at the third port. A modern DBM is a broadband device, for example 2-200 MHz, and comes in extremely compact packages with or without connectors. DBM s are very useful in a variety of applications. 

By detecting the beat either at u +u or <0j-(02 double balanced mixer, an error... 

Figure 17.8 is a block diagram of a typical I/Q detector network. The received down-converted IF signal is split and applied to the input to two double balanced mixers, whose reference (LO) inputs are quadrature... 

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