• Pre-trimmed Blackmer®
Voltage Controlled Amplifier (VCA)
• RMS-Level Detector
• Wide supply voltage range: ±4.5V ~ ±16V
• Low supply current: 3.5 mA typ. (±15V)
• Wide dynamic range:
117 dB (VCA)
60 dB (RMS-level detector)

Datasheet Download

Datasheet Download
4305 Datasheet (236 kB)
Low Cost Analog Engine Dynamics Processor


• Compressors & Limiters
• Gates & Expanders
• AGCs
• Line-operated dynamics processors
• De-Essers
• Duckers
• Mixers
• Level indicators
• Companding noise reduction systems


The THAT4305 is a single-chip Analog Engine optimized for low-cost applications. It incorporates a high-performance Blackmer® voltage-controlled amplifier (VCA) and log-responding RMS-level sensor. The VCA and RMS detector are pre-trimmed at wafer stage to deliver low distortion without further adjustment.

Key Specifications(see4305 datasheetfor complete specifications)
Parameter Conditions Typical Units
Power supply voltage ±4.5 to ±16 V
Supply current ±15V 3.5 mA
Dynamic Range 117 dB
Gain Range -60 to +60 dB
Total Harmonic Distortion 0.07 %
Control Constant
(both positive & negative- sense control available)
± 6.2 mV/dB
Output Noise 0 dB gain -97.5 dBV
RMS Detector
Averaging Method Root Mean Squared (RMS)
Output Scaling +6.2 mV/dB
Dynamic Range 60 dB
Bandwidth > 20 kHz
Crest Factor 1 dB reading error 10
Model Package Order Number Pricing (1000) Min Order Quantity Samples
4305 16 Pin QSOP 4305Q16-U $3.22 98 Request Samples
16 Pin QSOP Tape & Reel 4305Q16-UR Contact us 2000
4305 Demo System 4305-DEMO $100 1

All 4305 parts are RoHS compliant. Minimum Order Quantity (MOQ) is one tube or one reel. Parts must be ordered in multiples of the MOQ. Samples are available for qualified applicants. Pricing is subject to change. 

ICs designated -UR are available on tape and reel for a modest increase in price and require an extended lead time. Please contact our sales department for pricing and current lead time.

Design Notes (as PDF files)

Design Note 00A   Basic Compressor/Limiter Design (113k) (formerly Application Note 100A)

Design Note 01A   The Mathematics of Log-Based Dynamic Processors (64k) (formerly Application Note 101A)

Design Note 02  Digital Gain Control with Analog VCAs (106k) (formerly Application Note 102)

Design Note 03  Signal Limiter for Power Amplifiers (95k) (formerly Application Note 103)

Design Note 04   Improving Loudspeaker Signal Handling Capability (217k) (formerly Application Note 104)

Design Note 05   A Low Parts Count, Two-Slope Compressor (78k) (Application Note 105)

Design Note 100   A Fully Adjustable Noise Gate (69k)

Design Note 101   Peak Detection with the THAT4301 (37k)

Design Note 102   Adjustable Ducker using the THAT 4301 (76k)

Design Note 107/111   A Simple Effective Soft-Knee Compressor / Limiter (81k)

Design Note 108   Single Chip Automatic Gain Control  (73k)

Design Note 112   LED Bar-Graph Compression Indictor (83k)

Design Note 113   THAT4301 Gain Reduction Indicator (33k)

Design Note 114   Adaptive Attack and Release Rates using THAT RMS Detectors (48k)

Design Note 115   Fully Adjustable Compressor/Limiter (46k)

Design Note 116   Techniques for Stereo Volume Control (126k)

Design Note 117   Input Limited for ADCs (120k)

Design Note 118   High Performance Stereo AGC (90k)

Design Note 119   Wide Ranging dB Meter (177k)

Design Note 125   The “One Knob Squeezer”  (90k)

Design Note 128   What’s a PTAT Temp. Coefficient, & Where Does It Come From?  (64k)

Design Note 131   Dealing with the PTAT Coefficient (75k)

Design Note 132   Alternate Method of Indicating Compression (52k)

Other Analog Engines  
THAT 4320 Low-voltage, low-power versatile Analog Engine for single supply voltages. 4320 Datasheet
THAT 4315 Low-voltage, low-power basic Analog Engine for single supply voltages. 4315 Datasheet
THAT 4316 Very low-voltage, low-power basic Analog Engine for single supply voltages. 4316 Datasheet
Voltage Controlled Amplifiers (VCAs)  
THAT 2180 Series Pre-trimmed Blackmer VCAs 2180 Series Datasheet
THAT 2181 Series Trimmable Blackmer VCAs 2181 Series Datasheet
THAT 2162 Dual Blackmer VCAs 2162 Datasheet

Analog Engine Selector
A side by side comparison of the features and specifications of our Analog Engine dynamic processor ICs.

4305 Demo Board – The THAT 4305 Demonstration System (US$100) allows the engineer to test the performance of a THAT4305 quickly and easily. The 4305 Demo Board is self-contained circuit board with XLR connectors for signal input and output and a 3-pin header for connection to an external regulated DC power supply (not included). See the 4305 Demo Board Datasheet for more information.

4305 Surface Mount Adapter Board – For our integrated circuits which are only available in surface mount packages THAT Corporation offers adapter boards which allow one of these surface-mount ICs to interface to a circuit board via traditional thru-hole mounting. These adapters make it easy for a design engineer to evaluate our surface-mount products on a prototype board without having to employ SMT technology. Adapter boards are available to qualified applicants.

Harsh Environment Packaging – TT Semiconductor repackages THAT Corporation’s IC products in ruggidized plastic for the medical, aerospace, defense, and heavy industrial marketplaces.

The History of VCAs – THAT Blackmer® VCAs are the successors to the original dbx® line of VCAs. Their development for professional audio use has a long history, and can provide some insight into the care and feeding of these essential devices.

4305 Material Data Declaration Sheet
Material Data Declaration Sheets (MDDS) disclose the hazardous materials in our integrated circuits as required by the European RoHS directive.