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Low Frequency Oscillator with Two Capacitor Multipliers

IP.com Disclosure Number: IPCOM000033932D
Publication Date: 2005-Jan-05
Document File: 4 page(s) / 76K

Publishing Venue

The IP.com Prior Art Database

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Low Frequency Oscillator with Two Capacitor Multipliers

Keywords: Low Frequency, Triangle Oscillator, Low Current

Background:

Shown herein is a simple low cost, low operation current, low frequency “on die” triangle oscillator (LFODTO) having two complementary capacitor multipliers.  The LFODTO shown has the advantages over prior art of easy to control capacitance multiplication, yet very low frequency operation (e.g., seventy Hz) and a reasonable branch current value (e.g., 500nA for cap multiplier).

  

Detailed Description of the Drawings:

             Referring to Fig.1, If the switch is closed, current Istart flows to the diode-connected M0 and is multiplied by the current mirror M1, M0(M1 has w/l N times larger compare to M0). Istart value is not critical, it only should be high enough to be higher (after mirroring – multiplying by N through M0, M1) compare to Io. In such a case (e.g., closed switch) the Vo voltage is almost zero (given by the saturation voltage of M1).  When the switch is open, the current Io starts to flow through M1 and the branch C – diode-connected M0. The feedback loop through C, M0, M1 sets the Ic (current through C) to the value which is given by the l/w ratio (N) of M1,M0:                                                              Ic = Io/(N+1)

      Since this ratio is high, the Ic can be very low and the capacitor is charged by a very low current which results in a slow charging of Co – i.e. slow Vo ramp is created. If the switch is closed, the Vo is quickly discharged back to zero (saturation voltage of M1). It is possible to build a saw-tooth oscillator just with this capacitance multiplier, however it is difficult to make a triangle signal (symmetrical), because only rising ramp is affected by the multiplication factor N – the falling edge is in fact given by the N*Istart current.                                ...