Name: TLC2652 weak signal amplification

Supply voltage range: maximum ± 8V

Dimensions: 44.5mm X 34mm


In measuring weak signals, it is often necessary to amplify microvolt level signals. In this case, an ordinary operational amplifier has been unable to use because of their input offset voltage is typically in the hundreds of micro-volts or more, and the temperature coefficient of the offset voltage is zero over a few microvolts. Although the input offset voltage can be zero, but it is difficult to eliminate drift.

Chopper-stabilized ways of working to make TLC2652 has excellent DC characteristics, offset voltage and drift, the common mode voltage, low-frequency noise, the power supply voltage, and so the op amp is reduced to a minimum, TLC2652 well suited for micro signal amplification.


TLC2652 internal functional units make a brief introduction:


1, the main amplifier. It differs from the general op amp is that it has three inputs. In addition to outside the chip lead inverting and inverting input terminal, its in-house chip and one for non-inverting input of zero.
2, zero amplifier. It also has three input terminals, but with the main amplifier contrary, in the chip's inputs are the inverting input.
3, a clock and a switch circuit. Internal clock generates a clock signal to control the respective switches at a certain timing closure and disconnection. In the 14 and 20-pin chip clock signal can be introduced from the outside.
4, the compensation network. It makes the circuit over a wide frequency band has a flat response. In TLC2652, the high frequency response of the circuit is mainly determined by the main amplifier.
5, the clamping circuit (CLAMP). It is actually a difference between the supply voltage when the output approaches the 1V switching operation, the CLAMP and the inverting input of op amp short, the introduction of its deep negative feedback circuit gain can significantly decrease overload to prevent saturation. It can speed up recovery after a circuit overload.

In the choice of components that require special attention is the circuit of the two memory capacitors CXA and CXB must use high quality capacitors insulation resistance. For example, polyester film capacitors, polystyrene capacitors, polypropylene capacitors and other capacitors can be used as memory capacity can choose from 0.1μF to 1μF, the capacitor connected to one end of CXA or CXB pin, and the other end to VDD- or C RETURN pins. In some chopper-stabilized op amp is connected to the memory capacitor VDD- pin will increase noise, and TLC2652 is no such problem.

1, very low input offset voltage: 0.5μV (typ), 1μV (max);
2, low offset voltage drift: 0.003μV / oC (typical), the offset voltage long-term driftShift 0.003μV / month;
3, low input bias current: 4pA (typ), 60pA (max);
4, low input offset current: 2pA (typ), 60pA (maximum), 500pA (T = - 55 oC to 125 oC maximum);
5, the open-loop voltage gain: 135dB (minimum), 150dB (typ);
6, CMRR: 120dB (minimum), 140dB (typ);
7, the power supply rejection ratio: 110dB (minimum), 135dB (typ);
8, the supply current: 1.5mA;
9. Gain Bandwidth Product: 1.9MHz;
10, input noise: 94 nV / √Hz @ f = "10Hz", 23 nV / √Hz @ f = "1kHz";
11, the swing speed: 2.8V / μs (SR +), 3.1 V / μs (SR-);
12, the power supply voltage: 16V (VDD + -VDD -) (max);
13, the output current: ± 50mA.

TLC2652 is precision amplifier, often in the input voltage at the order of microvolts case of a high gain work. To ensure the accuracy of the amplifier, first negative feedback resistor must have sufficient precision and the closed-loop gain of the circuit is not too large; the second is the need to improve the quality of the printed circuit board, to prevent the leakage current of the plate surface. To do this, a guard ring on a printed circuit board, in particular 14-pin and 20-pin chip, can take advantage of the input air around the foot guard ring structure.


TLC2652 overload recovery time is relatively short (30ms or so), such as to further reduce the recovery time, you can use the CLAMP pin circuit. In this case, the circuit of negative feedback resistor to choose bigger, so that when you play the role of the clamp circuit gain decreased even more. Of course, the use of CLAMP, output amplitude circuit will be slightly reduced. Like other CMOS devices, TLC2652 also parasitic thyristor effect, when using a 200-510Ω limiting resistor in series in the positive and negative power supply, while ensuring not to input and output voltage of the circuit beyond the supply voltage 300mV.


 

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