This circuit (see photo) to use a PNP transistor V1 as a temperature sensor, dual timer 556 (IC1) as the frequency conversion. V1 V1 output current of the capacitor charge, when the power reaches C1 + E 2 / 3, IC1A output goes low, C1 quickly discharges. As the role of D1 clamping until the voltage across C1 close to zero, IC1A output recovery is high, C1 to recharge. IC1A recovery time is less than 1uS, the output duty cycle rectangular wave of 1. IC1A output trigger monostable trigger IC1B, to obtain a constant pulse width, repetition rate and temperature is proportional to the rectangular pulse output V0.

When the temperature is from 0 to 100 , the output frequency range from V0 to 3.4 KHz-5KHz, linearity error of less than ± 0.5 .
  The figure can IC1 LM556, NE556, etc., D1 use 2AK diode, V1 model limitation, as long as both PNP silicon tube. + E = +5- +12 V.