The CA3140 is HeroMicro a unique BiMOS operational amplifier that combines a PMOS FET input stage with a bipolar output stage. This hybrid architecture delivers the ultra-high input impedance of MOSFETs and the strong output drive of bipolar transistors, making it ideal for single-supply, low-power, and high-impedance signal conditioning applications such as photodetection, sample-and-hold, peak detection, active filtering, comparators, and portable instrumentation.
1. Key Features (from CA3140.pdf)
Supply Voltage: 4V to 36V single, or ±2V to ±18V dual
Input Impedance (ZIN): Typ. 1.5 TΩ (1.5 × 10¹² Ω), with input bias current of only 10 pA (@±15V)
Common-Mode Input Range (VICR): Extends 0.5V below the negative rail (e.g., accepts –0.5V when V– = 0V)—ideal for single-supply, ground-referenced systems
Gain-Bandwidth Product (GBW): 4.5 MHz
Slew Rate: 9 V/μs
Output Swing: Near rail-to-rail (+13V / –14.4V @ ±15V)
Input Offset Voltage (VIO): Typ. 5 mV, Max 15 mV (externally nullable)
Package: DIP-8 or SOP-8
Pin 8 (STROBE): Special function—sinking ≥220 μA to V– forces output low
Internal Compensation: Unity-gain stable; external capacitor can be added for additional roll-off
2. Key Usage Guidelines
(1) Ultra-High Input Impedance for Weak Signals
The 1.5 TΩ input impedance and 10 pA bias current make it perfect for photodiode transimpedance amplifiers (TIA), pH electrodes, and high-Z sensor interfaces.
PCB layout is critical: Use guard rings around input traces to minimize leakage and noise pickup.
(2) True Single-Supply “Ground-Referenced” Operation
Input common-mode range goes 0.5V below V–, so with V– = 0V (single supply), it can process signals down to –0.5V, including 0V.
Output also swings close to ground (typ. 0.13V @ 5V supply)—ideal for 5V TTL/CMOS system interfacing.
(3) Direct Replacement for 741 in Most Applications
Pin-compatible with the industry-standard μA741. Can directly upgrade 741-based designs requiring high input impedance and single-supply operation.
(4) Offset Voltage Nulling
Pins 1 and 5 are offset null terminals. Typical connection: a 10 kΩ potentiometer between pins 1 and 5, with the wiper tied to V–, allows VIO adjustment to near zero.
(5) STROBE Function (Pin 8)
Leave open or tie to V+ for normal operation.
To force output low, sink ≥220 μA from STROBE to V–—useful for analog multiplexing, sample-and-hold gating, or low-power standby control.
(6) Stability and Compensation
Internally compensated for unity-gain stability. For extra high-frequency noise suppression, add a small capacitor (10–100 pF) between pin 8 and V– to roll off bandwidth.
(7) Output Protection
Built-in short-circuit protection to either supply rail or ground enhances system robustness.
3. Typical Applications
Photodiode transimpedance amplifier (TIA)
Front-end for portable medical/environmental sensors
Single-supply active low-pass/high-pass filters
Peak detectors and envelope demodulators
Voltage comparators (open-loop)
Analog signal conditioning for 5V microcontroller systems
Long-duration timers and multivibrators
4. Summary
The CA3140 stands out with its MOSFET-input ultra-high impedance, true single-supply ground-referenced capability, 4.5 MHz bandwidth, and 741 pin compatibility. By leveraging its offset null, STROBE, and compensation features, designers can build high-performance, reliable analog front-ends for demanding low-power and high-impedance applications.
