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6. Block diagram
The block diagramme of AMT-07M is presented in fig.11. The amplifier
functionally consists of the photodetector with PD, temperature sensor RT, Peltier
element P and amplification-transformation circuit including preamplifier
А
1,
bandpass amplifier
ВА
, variable gain amplifier A2, synchronous demodulator SD,
multiplexer MX, analog-to-digital converter ADC and liquid crystal display LCD,
as well as regulating-stabilizer circuit of PD temperature including amplifiers
А
3,
А
4 and pulse power supply converter of Peltier element DRVP. The amplifier
feeding is implemented with the DC / DC circuit, which is a pulse voltage
converter from + 12 V in + 5 V, -5 V. The input voltage of DC / DC converter
supplies from +12 VDC jack.
Signal from the output of the photodetector comes to the preamplifier
А
1. It is
enclosed in a metal shield for noise minimization. From the output of the
preamplifier
А
1 the signal comes to the bandpass amplifier
ВА
, which gain the
signal in the band from 500 Hz to 50 kHz, and after that to the variable gain
amplifier
А
2. The amplification can be changed by the button "Amplif. Coeff".
The value of amplification is indicated by light-emitting diodes “1”, “10” and
“100”.
From the output of the variable gain amplifier
А
2 the signal comes to the jack
OUTPUT and for rectification to the synchronous demodulator SD, which receive
clock pulses from the jack SYNCHRO.
The multiplexer MX2 switch the direct voltages from:
- the output of the synchronous demodulator SD (The voltage is
proportional to the signal amplitude).
- the potentiometer RP1 (The voltage is proportional to the installed PD
temperature).
- the amplifier A3 (The voltage is proportional to the current PD
temperature).
Voltage from the output of MX2 feed to the analog-digital converter ADC and
then to the liquid-crystal indicator LCD DISPLAY. The display mode can be
selected with the help of button "Display mode".
The circuit executed on DRVP, A3, A4 is used for stabilisation and
adjustment of PD temperature. Stabilisation and temperature adjustment is carried
out by means of Pelte element P. The temperature sensor is based on the
thermoresistor RT. The signal from the temperature sensor after amplification by
A3 supplies on the first input of the error amplifier A4. The reference voltage from
potentiometer RP1 supplies on the second input of A4. The converter DRVP
generates the voltage on the Peltier element which changes the temperature of the
PD and supports its at the level set by the potentiometer "T
adjust
". The DRVP begin
working after pressing the button "Cooler ON / OFF". Then cooling is working the
light-emitting diode “Start cooling” is shining. Integrated temperature controller
allows to maintain the temperature of PD in the range from -10 ° C to +25 ° C.