# Zoom Amplifier

This “unusual zoom amplifier circuit” allows you to “zero out” a DC voltage and then amplify a small AC signal which is superimposed on the much larger DC level. When switch SW1 is closed, both INA128 inputs see the same AC + DC level and its high common- mode rejection results in zero volts output. When SW1 is opened, the DC level is stored on C1 but now the AC signal is applied to only the inverting input where it is amplified by a factor of 1000x. The droop rate of C1 depends on the leakage of SW1 and the input bias current of U1.Using a glass reed relay and an INA116 (Ib = 5fA typ), extremely low droop rate can be achieved. A high insulation resistance dielectric capacitor is necessary– teflon, polystyrene, etc. (Circuit is created by Neil P. Albaugh  TI- Tucson)

## Online Simulation of a Zoom  Amplifier Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself, or  watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

# Current Shunt Amplifier

This current shunt monitor circuit allows a current measurement to be made by measuring the voltage drop across a shunt resistor in the “high side” of a power supply. The INA193 is capable of operating with a common- mode voltage of up to +80V and its CMV range is not a function of
its supply voltage.  The INA193 provides a differential voltage gain of 20V/V and its recommended full- scale input  voltage is 100mV.  An INA194 provides a gain of 50V/V and an INA195 provides a gain of 100V/V. R1 & R2 together with C2, C3, & C4 provide differential and common-mode filtering and are recommended for switching power supplies. The two resistors should be carefully matched (1% tolerance) as well as capacitors C3 & C4 (5% or better tolerance). Resistors of 100 ohms will give a gain error of slightly under 2%. (Circuit is created by Neil P. Albaugh,  TI – Tucson)

Current Shunt Amplifier circuit:

## Online Simulation of the Current Shunt Amplifier Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself, or  watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

# Proportional- Integral Temperature Control

A high- accuracy temperature control amplifier can be realized with a proportional- integral amplifier response; the integrator function drives the steady- state error to zero.  An autozero instrumentation amplifier INA326 achieves very low offset and drift as well as virtually eliminating the loop error due to 1/f noise. R6 is used simply to provide a feedback path during a DC analysis. This circuit requires an overall feedback path (TEC, etc) to achieve a steady-state operating point. This amplifier allows temperature control loop stability within in a few tens of milli- degrees. Bypass capacitors are not shown. This circuit can be used with a DRV593 or an OPA569 TEC driver circuit. (Circuit is created by Neil P. Albaugh  TI – Tucson)

## Online Simulation of the Proportional- Integral Temperature Control Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself, or  watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

# Capacitance Multiplier

A “capacitance multiplier” circuit can increase the effective value of a small capacitor C1 to a much larger value. The capacitance  seen at Vout is: Cout = C1 * R1/R3. Note that this circuit is only for a ground- referenced capacitor. Rs = R3. The output capacitance can be verified by placing an AC source in series with a resistor tied to Vout and running an AC frequency  response analysis. As seen in the result below, the 100pF capacitor has been multiplied by 1,000. Bypass capacitors are not shown.  (From a NSC app note) Circuit is created by Neil P. Albaugh  TI – Tucson

## Online Simulation of the Capacitance Multiplier Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself, or  watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

# OPA569 Laser Driver

The “OPA569 Laser Driver” circuit provides voltage- controlled constant- current biasing of a grounded- anode laser diode by using a negative supply voltage and a positive control voltage.  As shown, the OPA569 op amp provides an output current of 500mA per volt input. Output is current- limited to 2A by R2. Frequency compensation is provided by C3 R3. This circuit takes advantage of the unique topology of the OPA569; it does not require a shunt resistor to measure its output current. This amplifier provides an output monitor current from pin 19 that is 1/475 th of its output current. This current is used as negative feedback to the amplifier’s inverting input (pin 5).  A constant- current output is derived by this feedback.
Since no shunt resistor is required to measure output current, there is no reduction in output voltage compliance due to shunt resistor voltage drop and this circuit can swing its output voltage very close to its supply rail. This increases efficiency and reduces heat sinking requirements. In fact, supply voltage can be reduced to 3.3V  for most laser diodes.
The OPA569 features both a Current Limit (pin 4) and a Thermal Overtemp (pin 7) flag. These flags can be used to protect the amplifier and the Enable (pin 8) can be used to digitally control its status. (Circuit is created by Neil P. Albaugh,  TI – Tucson)

OPA569 Laser Driver Circuit

## Online Simulation of the OPA569 Laser Driver Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud and analyze the circuit or watch our tutorial video.

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

# Universal Voltage Reference

“This universal voltage reference circuit”- can provide a reference voltage that is continuously adjustable between -10V and +10V. If a REF02 is substituted for the  REF102 shown here, the output range will be -5V to +5V.The circuit uses both an op amp inverting gain path and a non- inverting  gain path simultaneously.  A potentiometer controls the ratio of these two gain paths. With the potentiometer wiper arm grounded,  U1 operates as an ordinary inverting amplifier with a gain of -1V/V. When the wiper arm is rotated to the other end of the potentiometer,  however, there is an additional gain path of +2V/V in addition to the -1V/V path. The resulting sum is a gain of +1V/V. At 50% rotation  (the wiper arm is exactly centered) the non- inverting gain path drops to +1V/V— cancelling the -1V/V gain entirely.  The output is then 0V. P1 should be a good quality potentiometer with high resolution and a good temperature coefficient.  Fortunately, the TC match of the resistance ratios of a potentiometer is much lower than its absolute resistance TC. (Circuit is created by Neil P. Albaugh  TI- Tucson)

Universal Voltage Reference

## Online Simulation of the Universal Voltage Reference Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

# Differential Amplifier CMRR Trim Circuit

Adding a negative- resistance circuit (U2) to the REF pin allows the CMRR of a differential amplifier or instrumentation amplifier to be trimmed. This is done by applying a sine wave of 20Vp-p to the inputs of U1 and adjusting the potentiometer P1 for a minimum signal at the amplifier output. By using an AC source the DC input offset errors do not effect this trim. At 50% rotation of P1 the resistance of R8 cancels the resistance of R5, appearing as a virtual ground to the REF pin. As P1 is adjusted from end to end, R5 is “undercancelled”or “overcancelled” by R8 and the resistance presented to the REF pin goes from a real, positive resistance to a negative resistance. This allows the internal resistor network of U1to be trimmed for maximum CMRR. ( Circuit is created by Neil P. Albaugh  TI – Tucson )

Differential Amplifier CMRR Trim Circuit

## Online Simulation of the Differential Amplifier CMRR Trim Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.